192vertebrate anatomy morphology palaeontology 9:192 issn 2292-1389 vertebrate anatomy morphology palaeontology is an open access journal http://ejournals.library.ualberta.ca/index.php/vamp article copyright by the author(s). this open access work is distributed under a creative commons attribution 4.0 international (cc by 4.0) license, meaning you must give appropriate credit, provide a link to the license, and indicate if changes were made. you may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use. no additional restrictions — you may not apply legal terms or technological measures that legally restrict others from doing anything the license permits. corrigendum: a new species of hydrochoerus (rodentia: caviidae: hydrochoerinae) from the pleistocene of san diego county, california, usa with remarks on capybara biogeography and dispersal in the pleistocene of western north america richard s. white1*, jim i. mead1,2, thomas a. deméré3, and gary s. morgan4 1the mammoth site, hot springs, south dakota, usa 57747; rswhite@mammothsite.org 2desert laboratory on tumamoc hill, university of arizona, tucson, arizona, usa 85745 3san diego natural history museum, san diego, california, usa 92112 4new mexico museum of natural history and science, albuquerque, new mexico, usa 87104 published march 6, 2022 *corresponding author. © 2022 by the authors. doi 10.18435/vamp29383 we provide the following correction for the caption of figure 9, on page 143 of white, r.s., j.i. mead, t.a. deméré and g.s. morgan. 2022. a new species of hydrochoerus (rodentia: caviidae: hydrochoerinae) from the pleistocene of san diego county, california, usa with remarks on capybara biogeography and dispersal in the pleistocene of western north america. vertebrate anatomy, morphology, palaeontology, 9:131–155. it should read as follows: figure 9. ontogenetic series of right maxillary tooth rows in hydrochoerus hydrochaeris. a, age class i with no wear on anter ior teeth (mscc 456); b, age class i with wear on all teeth (mscc 457); c, age class ii (mscc 463); d, age class iii (mscc 461); e, age class iv – v (mscc 462); f, age class vii (mscc 460). measurements of the upper third molar (m3) are provided in table 5. mailto:rswhite@mammothsite.org brinkman et al erratum.indd 61vertebrate anatomy morphology palaeontology 3:61-62 issn 2292-1389 vertebrate anatomy morphology palaeontology is an open access journal http://ejournals.library.ualberta.ca/index.php/vamp article copyright by the author(s). this open access work is distributed under a creative commons attribution 4.0 international (cc by 4.0) license, meaning you must give appropriate credit, provide a link to the license, and indicate if changes were made. you may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use. no additional restrictions — you may not apply legal terms or technological measures that legally restrict others from doing anything the license permits. erratum: non-marine fishes of the late santonian milk river formation of alberta, canada – evidence from vertebrate microfossil localities donald b. brinkman,*,1,2 andrew g. neuman1 and julien d. divay1 1royal tyrrell museum of palaeontology drumheller, alberta, t0j 1b0, canada; don.brinkman@gov.ab.ca 2adjunct, department of biological sciences, university of alberta edmonton, alberta canada t6g 2e9 *corresponding author published april 11, 2017 © 2017 by the authors doi 10.18435/b5d598 in our recent publication of the fishes from the milk river formation (brinkman et al. 2017), figure 20 was replaced in final editing by a duplication of figure 21. the correct figure 20 is presented on the opposite page. figure 20. acanthomorph centra from the milk river formation. a–c) first centra showing variation in the development of struts along the side of the centrum: a, ualvp 56052; b, ualvp 48903; c, tmp 2000.2.57. d–f) precaudal centra showing variation in development of struts and ridges on the lateral and dorsal surface of the centrum: d, ualvp 48907; e, ualvp 17397(a); f) ualvp 17397(b). centra shown in anterior, left lateral, posterior, dorsal and ventral views. scale bar equals 2 mm. literature cited brinkman, d.b., a.g. neuman, and j.d. divay. 2017. nonmarine fishes of the late santonian milk river formation of alberta, canada evidence from vertebrate microfossil localities. vertebrate anatomy morphology palaeontology 3:7-46. vertebrate anatomy morphology palaeontology 3:61-62 62 68vertebrate anatomy morphology palaeontology 7:68 issn 2292-1389 vertebrate anatomy morphology palaeontology is an open access journal http://ejournals.library.ualberta.ca/index.php/vamp article copyright by the author(s). this open access work is distributed under a creative commons attribution 4.0 international (cc by 4.0) license, meaning you must give appropriate credit, provide a link to the license, and indicate if changes were made. you may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use. no additional restrictions — you may not apply legal terms or technological measures that legally restrict others from doing anything the license permits. addendum: table 2. a juvenile cf. edmontosaurus annectens (ornithischia, hadrosauridae) femur documents a previously unreported intermediate growth stage for this taxon andrew a. farke1,2,3,* and eunice yip2 1raymond m. alf museum of paleontology, 1175 west baseline road, claremont, ca, 91711, usa 2the webb schools, 1175 west baseline road, claremont, ca, 91711, usa 3dinosaur institute, natural history museum of los angeles county, 900 exposition blvd. los angeles, ca, 90007, usa; afarke@webb.org published may 2, 2019 *corresponding author. © 2019 by the authors submitted dec. 18, 2019; revisions received april 22, 2019; accepted april 25, 2019. handling editor: robert holmes. doi 10.18435/vamp29350 table 2. measurements of femora from edmontosaurus, in millimeters, used for regression analysis. all measurements from wosik et al. (2018), except for ualvp specimens (baert et al., 2014; vanderven et al., 2014) and ram 9396 (this study). specimen species length (mm) circumference (mm) amnh 5730 e. annectens 1148 512.3 ccm disarticulated e. annectens 875 337.5 ccm v 1938.8 e. annectens 1152 490 cmn 8509 e. annectens 995 417.5 cmnh 10178 e. annectens 910 330 dmnh 1493 e. annectens 1035 459.5 fpdm e. annectens 990 344 lacm 23504 e. annectens 559 220 mor 2939 e. annectens 1175 509 ram 9396 e. annectens 277 105 sdsm 4917 e. annectens 1032 381 ucmp 128181 e. annectens 148 60 ucmp 137278 e. annectens 995 425 usnm 2414 e. annectens 1025 388.5 ypm 2182 e. annectens 1025 490 cmn 2289 e. regalis 1243 532 cmn 8399 e. regalis 1140 374 rom 801 e. regalis 1280 480 rom 867 e. regalis 990 422.5 ualvp 52758 e. regalis 860 266 ualvp 50988 e. regalis 515 208 mcfeeters et al response.indd 73vertebrate anatomy morphology palaeontology 6:73-74 issn 2292-1389 vertebrate anatomy morphology palaeontology is an open access journal http://ejournals.library.ualberta.ca/index.php/vamp article copyright by the author(s). this open access work is distributed under a creative commons attribution 4.0 international (cc by 4.0) license, meaning you must give appropriate credit, provide a link to the license, and indicate if changes were made. you may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use. no additional restrictions — you may not apply legal terms or technological measures that legally restrict others from doing anything the license permits. we agree that the pedal unguals from the arundel clay described by brownstein (2017) more likely belong to ornithomimosaurs than to any other theropod clade, and treated them as such in our original discussion (mcfeeters et al. 2018). we thank brownstein (2018) for providing further elaboration of morphological characters that may be useful for distinguishing ornithomimosaur pedal unguals from those of other theropods. we interpret the character of a triangular cross-section, which we do not dispute occurs in ornithomimosaur pedal unguals, to refer to the overall morphology of the ungual being grossly defined by having relatively distinct ventral, dorsomedial, and dorsolateral surfaces, such that a section taken along an arbitrary point along the length of the ungual can be considered generally triangular. however, this characterization of a generalized section of the ungual is not necessarily an adequate description of the specific outline of the proximal facet, which must articulate with the corresponding penultimate phalanx, and varies according to position within each pes. while it is possible that two (or more) ornithomimosaur taxa are represented by the pedal unguals currently known from the arundel clay, the appropriate null hypothesis in this situation is that no taxonomic variation is present in the sample, and the burden of evidence is on demonstrating that the two morphotypes must belong to different taxa. we concluded that the differences noted by brownstein (2017) resemble the type of positional ungual variation we observed in related taxa from alberta, and therefore do not offer a compelling case for rejecting the null hypothesis. the range of expected intraspecific variation in ornithomimosaur pedal unguals has largely not been quantified, and further work is needed if brownstein’s claims on this topic are to be supported. for example, whether or not the degree of dorsoventral curvature is judged to support taxonomic separation of the two morphotypes is at this point little more than a matter of opinion. the objective of our short paper was to document consistent patterns of variation between different pedal ungual positions in ornithomimids, rather than to establish ranges of intraspecific variation for all pedal ungual characters. while we distinguished between characters that can be considered diagnostic of position in the pes and those that are not consistently informative in this regard, observed variation was not limited to the former category. as many of the specimens in our study were only figured in proximal and ventral view, it is not apparent how brownstein has estimated the range of variation present in our sample in characters more appropriately observed in medial and lateral view, such as the prominence of the grooves for the claw sheath. the form of the proximodorsal process and the claw sheath grooves were mentioned in the summation of the digit iii ungual morphology as examples of their symmetry, rather than to assign importance to the relative prominence of these features. regarding the other material described by brownstein, we reiterate our citation of osmólska et al. (1972: fig. 14) clearly showing a distinct flexor tubercle on all manual unguals of the ornithomimid gallimimus. in a struthiomimus manus figured by osborn (1917: fig. 3), the flexor tubercles of manual unguals ii and iii (following osborn; iii and iv of some authors) are hidden by the orientation of these unguals in dorsal view, but are visible in palmar view in the same figure (see also nicholls and russell 1985: fig. 8, for struthiomimus unguals in medial view). we view the robustness of the humerus, even if verified, as of dubious phylogenetic significance, since the distribution of this character suggests that a relatively robust humerus is the likely plesiomorphic condition for both harpymimus and ornithomimids (kobayashi and lü 2003: appendix 2). the most robust ornithomimid humeri, such response to brownstein (2018) ‘rebuttal of mcfeeters, ryan and cullen, 2018’ bradley mcfeeters1*, michael j. ryan1,2, and thomas m. cullen3 1dept. earth sciences, carleton university, ottawa, ontario, k1s 5b6, canada; bradleymcfeeters@cmail.carleton.ca 2cleveland museum of natural history, 1 wade oval drive, cleveland, ohio 41106-1767, usa; mryan@cmnh.org 3field museum of natural history, 1400 s lake shore drive, chicago, illinois 60605, usa; thomas.cullen@ fieldmuseum.org *corresponding author published july 16, 2018 © 2018 by the authors submitted july 10, 2017; accepted july 10, 2018. this article is part of a comment/response submission and therefore is not peer-reviewed. handling editor: robert holmes. doi 10.18435/vamp29343 vertebrate anatomy morphology palaeontology 6:73-74 74 as that of anserimimus, are comparable to harpymimus (kobayashi and barsbold 2006: fig. 6), so the robustness of the arundel element does not offer strong support for the grade of ornithomimosaur present. the aptian–albian is a critically interesting, yet incompletely understood interval in the history of ornithomimosaurs. it contains the globally youngest occurrences of (non-ornithomimid, non-deinocheirid) ‘basal ornithomimosaurs’ and oldest occurrences of possible basal deinocheirids (lee et al. 2014; sues and averianov 2016), and immediately precedes the oldest definitive occurrences of ornithomimids in the cenomanian–turonian of asia (sues and averianov 2016, and references therein), as well as preceding a possible hiatus in the presence of ornithomimosaurs from the cenomanian to santonian of north america (mcfeeters et al. 2016). the presence of coexisting basal and derived ornithomimosaurs in the aptian of north america would indeed have important larger evolutionary and palaeobiogeographic implications, if further work supports this interpretation. however, while we appreciate brownstein’s work for documenting new material of early cretaceous north american ornithomimosaurs, we remain cautious of such far-reaching claims given the current state of evidence. literature cited brownstein, c. d. 2017. description of arundel clay ornithomimosaur material and a reinterpretation of nedcolbertia justinhofmanni as an “ostrich dinosaur”: biogeographic implications. peerj 5:e3110, 1–20. brownstein, c. d. 2018. rebuttal of mcfeeters et al. 2018, ‘positional variation in pedal unguals of north american ornithomimids (dinosauria, theropoda): a response to brownstein (2017)’. vertebrate anatomy morphology palaeontology 6:68–72. kobayashi, y., and r. barsbold. 2006. ornithomimids from the nemegt formation of mongolia. journal of the paleontological society of korea 22:195–207. kobayashi, y., and j.-c. lü. 2003. a new ornithomimid dinosaur with gregarious habits from the late cretaceous of china. acta palaeontologica polonica 48:235–259. lee, y.-n., r. barsbold, p. j. currie, y. kobayashi, h.-j. lee, p. godefroit, f. escuillié, and tsogtbaatar c. 2014. resolving the long-standing enigmas of a giant ornithomimosaur deinocheirus mirificus. nature 515:257–260. mcfeeters, b., m.j. ryan, c. schröder-adams, and t.m. cullen. 2016. a new ornithomimid theropod from the dinosaur park formation of alberta, canada. journal of vertebrate paleontology 36:e1221415, 1–20. mcfeeters, b., m. j. ryan, and t. m. cullen. 2018. positional variation in pedal unguals of north american ornithomimids (dinosauria, theropoda): a response to brownstein (2017). vertebrate anatomy morphology palaeontology 6:60–67. nicholls, e. l. and a. p. russell. 1985. structure and function of the pectoral girdle and forelimb of struthiomimus altus (theropoda: ornithomimidae). palaeontology 28:643–677. osborn, h. f. 1917. skeletal adaptations of ornitholestes, struthiomimus, tyrannosaurus. bulletin of the american museum of natural history 35:733–771. osmólska, h., e. roniewicz, and r. barsbold. 1972. a new dinosaur, gallimimus bullatus n. gen., n. sp. (ornithomimidae) from the upper cretaceous of mongolia. palaeontologia polonica 27:103–143. sues, h.-d. and a. averianov. 2016. ornithomimidae (dinosauria: theropoda) from the bissekty formation (upper cretaceous: turonian) of uzbekistan. cretaceous research 57:90–110. acorn et al response to kellner.indd 90vertebrate anatomy morphology palaeontology 3:90–92 issn 2292-1389 vertebrate anatomy morphology palaeontology is an open access journal http://ejournals.library.ualberta.ca/index.php/vamp article copyright by the author(s). this open access work is distributed under a creative commons attribution 4.0 international (cc by 4.0) license, meaning you must give appropriate credit, provide a link to the license, and indicate if changes were made. you may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use. no additional restrictions — you may not apply legal terms or technological measures that legally restrict others from doing anything the license permits. kellner’s (2017) rebuttal to our paper (martin-silverstone et al., 2017) affords us an opportunity to further develop our position regarding the pterosaur specimen ualvp 24238. because three of us (martin-silverstone, glasier, and mohr) were in the final stages of thesis preparation, and currie was in the field, acorn was designated to compose our response in a timely fashion. however, all authors have seen, contributed to, and approved the following text. there are two broad areas of disagreement between our interpretation and that of kellner, and both go well beyond the study of pterosaurs per se. the first has to do with statistics, and the importance of assessing variation among individuals. the second has to do with the interpretation of equivocal evidence. a quick summary of our perspectives on these two points should guide other workers through this debate. before beginning this summary, however, we freely acknowledge that kellner is not a splitter in many of his other published works, and that we missed the difference between his rostral value and the rostral index of martill and naish (2006). he admits that he misread bennett (1992) and that ualvp 24238 is likely male, and we admit that the ontogenetic maturity of this specimen at death was likely more advanced than we thought. in our original paper (martin-silverstone et al., 2017), we note that bennett (1992) focuses on patterns in the data for pteranodon as a whole, whereas kellner (2010) focuses on similarities and differences between particular specimens. this difference, between what might be termed statistical and non-statistical approaches, is, in our opinion, the reason behind what kellner (2017) calls, “the importance of this debate for pterosaur research in general.” however, from a statistical perspective, the quantitative techniques involved here are very simple, so it is important to realize that this debate is not about the difference between good statistics and bad, it is about the difference between some statistics and none. in our paper, we provide novel quantitative details in support of the assignment of ualvp 24238 to pteranodon sternbergi, and these are the data that best support our argument (martin-silverstone et al., 2017, figs. 6 and 9 in particular). as well, we provide graphic, qualitative support for the idea that the mandible of ualvp 24238 is not distinct from other specimens of pteranodon (martinsilverstone et al., 2017, fig. 7). most importantly, we show that, whereas ualvp 24238 and kuvp 967 exhibit the shallowest rostral taper of any known pteranodon, the rostrum of cmnfv 41358 possesses an intermediate condition between these specimens and fshm vp 339 (martinsilverstone et al., 2017, fig. 9). kellner (2017) does not mention these data in his rebuttal. instead, he focuses on comparisons between only two specimens: ualvp 24238 and fhsm vp 339 (the holotype of pteranodon sternbergi). kellner maintains that because both are mature males, the differences between them (the shapes of the rostra and craresponse to kellner (2017) 'rebuttal of martin-silverstone, e., j.r.n. glasier, j.h. acorn, s. mohr, and p.j. currie, 2017' john h. acorn,1 elizabeth martin-silverstone,2 james r.n. glasier,3 sydney mohr,4 and philip j. currie4 1department of renewable resources, university of alberta, edmonton, alberta, canada, t6g 2h1, jacorn@ualberta.ca 2ocean and earth science, university of southampton, university road, southampton, uk, so17 1bj, e.g.martin@soton.ac.uk 3evolution and ecology research centre, school of biological, earth and environmental sciences, university of new south wales, sydney, new south wales 2052 australia, jglasier@student.unsw.edu.au 4department of biological sciences, university of alberta, edmonton, alberta, t6g 2e9, smohr@ualberta.ca, pjcurrie@ualberta.ca published august 11, 2017 © 2017 by the author submitted august 2, 2017; accepted august 3, 2017 this article is part of a comment/response submission and therefore is not peer-reviewed. handling editor: robert holmes doi 10.18435/b50om2c acorn et al. — response to kellner, 2017 91 nial crests) are taxonomic, not ontogenetic or the product of intraspecific variation. we appreciate how tempting it is to look at kellner’s (2017) figure 1, and conclude that these two specimens represent obviously different taxa. coincidentally, however, in a recent blog post, that appeared before our paper was published, another pterosaur specialist, mark witton (2016) presents a figure almost identical to kellner’s, superimposing outline drawings of the same two skulls plus kellner’s geosternbergia maiseysi holotype. revealingly, witton’s figure is presented in support of bennett’s position, not kellner’s. for us, the data that spring most strongly to mind during this discussion are the eleven size-frequency histograms in bennett (1992). they show, among other things, that some large (likely male) pteranodon were larger than others. if crest size, and the length of the crest base, was positively allometric with skull size, then it does not matter whether ualvp 24238 was a subadult, or an adult. what matters is that there was significant variation within pteranodon sternbergi. additionally, if the cranial crests of pteranodon were sexually dimorphic (bennett 1992; tomkins et al. 2010; hone et al. 2012; knell et al. 2013), then they were probably under the influence of sexual selection. in modern animals, sexually selected or “signal” traits are more variable than those of non-signal traits, with respect to their size, shape, colour, and presence/absence (e.g., alatalo et al. 1988; wiens 2001; cuervo and møller 2009; tazzyman and iwasa 2010; emlen et al. 2012). for this reason, it is both reasonable and parsimonious to expect significant morphological variation in the cranial crests of mature males of a single species of pteranodon. with respect to how one assesses equivocal evidence (such as poorly preserved fossils), kellner maintains that our logic, “contains in some parts indications of circular reasoning,” but does not elaborate on how he thinks our conclusions are embedded in our premises; the mark of circularity in logic. later in his text, however, kellner returns to a critique of our reasoning, and asserts that, with respect to the features he uses to diagnose dawndraco, “the morphological differences are there,” and that “although recognizing their existence, [we] have dismissed them by arguing postmortem distortion or incomplete preservation.” this criticism takes us into the realm of paleontological philosophy, and it deserves a careful response. incomplete preservation, by definition, necessitates that at least part of a fossil is, in fact, not there. the missing distal portion of the rostrum of ualvp 24238 is a clear example of a character that simply does not exist, and the putative total length of the rostrum is one of the eight characters used by kellner to diagnose dawndraco kanzai. then there are the caudal vertebrae, which kellner mis-measured. again, the character does not exist, although a different structure does. kellner’s skull angle character clearly cannot be measured with any precision, for lack of discrete landmarks, and because of postmortem distortion. in this instance, the character is an approximation—a value with an uncertain range of potential error. when one thinks statistically, the existence or non-existence of particular features becomes a matter of probability, not a matter of presence or absence, or directly observable fact. in our paper, we show that four of kellner’s other diagnostic characters each fall within a range of continuous variation that appears to characterize pteranodon specimens as a whole. the existence or non-existence of these characters is not at issue—what is at issue is the existence of broad patterns of variation, which we recognize and find instructive. finally, the lacrimal process certainly exists on ualvp 24238, but is absent in other specimens because of (we suggest) incomplete preservation. postmortem distortion and incomplete preservation both exist in ualvp 24238 (although in a different sense than structural characters exist), and in the vast majority of other pterosaur specimens, and should not be rationalized away, no matter how tempting it is to see a different-looking specimen as representing a different taxon. when evidence is equivocal, and thus difficult to interpret in a straightforward fashion, a scientist should be cautious of perceptual errors. in almost all sciences, the primary safeguard against such errors is the application of quantitative analyses, and the search for objectively demonstrable patterns in nature. this is just as true in paleontology as in other fields, and quantitative studies of pteranodon, beginning with bennett (1992), are an outstanding example of this approach. in summary, we continue to base our opinion on the fact that the known pteranodon specimens form a bimodal size continuum, probably anagenetic, just as bennett demonstrated some 25 years ago. very few skulls possess complete rostra, or complete crests, and we therefore remain open minded regarding the variety of shapes that may have been present over the evolutionary history of the genus, the ontogenetic history of individuals, or among individuals in a population. although we acknowledge that future research or new discoveries may validate dawndraco kanzai as a distinct taxon, we feel that the characters currently used to distinguish it from pteranodon sternbergi are more parsimoniously interpreted within the framework of individual, ontogenetic and/or sexual variation, and preservational differences between ualvp 24238 and other pteranodon specimens. acknowledgements e. martin-silverstone would like to acknowledge the input of david hone on the subject of sexually selected traits. vertebrate anatomy morphology palaeontology 3:90-92 92 dr af t literature cited alatalo, r.v., j. höglund, and a. lundberg. 1988. patterns of variation in tail ornament size in birds. biological journal of the linnean society 34:363‒374. bennett, s.c. 1992. sexual dimorphism in pteranodon and other pterosaurs, with comments on cranial crests. journal of vertebrate paleontology 12:422‒434. cuervo, j.j., and a.p. møller. 2009. the allometric pattern of sexually size dimorphic feather ornaments and factors affecting allometry. journal of evolutionary biology 22:1503‒1515. emlen, d.j., i.a. warren, a. johns, i. dworkin, and l. corley lavine. 2012. a mechanism of extreme growth and reliable singling in sexually selected ornaments and weapons. science 17:860‒864. hone, d.w.e., d. naish, and i.c. cuthill. 2012. does mutual sexual selection explain the evolution of head crests in pterosaurs and dinosaurs? lethaia 45:139‒156. kellner, a.w.a. 2017. rebuttal of martin-silverstone et al. 2017, ‘reassessment of dawndraco kanzai kellner 2010 and reassignment of the type specimen to pteranodon sternbergi harksen, 1966’. vertebrate anatomy morphology palaeontology 3:81–89. kellner, a. w. a. 2010. comment on the pteranodontidae (pterosauria, pterodactyloidea) with the description of two new species. anais da academia brasileira de ciências 82:1063‒1084. knell, r.j., d. naish, j.l. tomkins, and d.w.e. hone. 2013. sexual selection in prehistoric animals: detection and implications. trends in ecology and evolution 28:38‒47. martill, d. m., and d. naish. 2006. cranial crest development in the azhdarchoid pterosaur tupuxuara, with a review of the genus and tapejarid monophyly. paleontology 49:925‒941. martin-silverstone, e, j.r.n. glasier, j.h. acorn, s. mohr, and p.j. currie. 2017. reassessment of dawndraco kanzai kellner, 2010 and reassignment of the type specimen to pteranodon sternbergi harksen, 1966. vertebrate anatomy morphology palaeontology 3:47‒59. doi 10.18435/b5059j tazzyman, s.j., and y. iwasa. 2009. sexual selection can increase the effect of random genetic drift – a quantitative genetic model of polymorphism in oophaga pumilio, the strawberry poison-dart frog. evolution 64:1719‒1728. doi:10.1111/j.15585646.2009.00923.x tomkins, j.l., n.r. lebas, m.p. witton, d.m. martill, and s. humphries. 2010. positive allometry and the prehistory of sexual selection. american naturalist 176:141‒148. wiens, j.j. 2001. widespread loss of sexually selected traits: how the peacock lost its spots. trends in ecology and evolution. 16:517‒523. doi: 10.1016/s0169-5347(01)02217-0 witton, m. 2016. the “pteranodon complex” and dismantling our understanding of the most famous flying reptile. accessed july 11, 2017 at: http://markwitton-com.blogspot.ca/2016/07/ the-pteranodon-complex-and-dismantling.html 1vertebrate anatomy morphology palaeontology 8:1-6 issn 2292-1389 vertebrate anatomy morphology palaeontology is an open access journal http://ejournals.library.ualberta.ca/index.php/vamp article copyright by the author(s). this open access work is distributed under a creative commons attribution 4.0 international (cc by 4.0) license, meaning you must give appropriate credit, provide a link to the license, and indicate if changes were made. you may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use. no additional restrictions — you may not apply legal terms or technological measures that legally restrict others from doing anything the license permits. robert “bob” lynn carroll, friend, mentor and scholar, died on april 7th, 2020, at the age of 81. bob, who had endured symptoms of dementia for several years, succumbed to complications arising from an infection by the novel coronavirus. we are deeply saddened to write this memorial, and on behalf of bob, dedicate it to his family (he is survived by his loving wife anna di turi, son david carroll, and granddaughter juliette), all of his past students graduate and undergraduate his past postdoctoral fellows, his close friends and his numerous colleagues from around the world, and to the members of the academic societies he so loved and cherished, the canadian society of vertebrate palaeontology, and the society of vertebrate paleontology. bob enjoyed a nearly 40–year career as a mcgill professor (1964-2003) – 57 years in total as professor and professor emeritus. for the first 15 years of retirement, he maintained regular work days in his office, split between publishing his science, regaling museum staff with details of his research, and swearing at his email software. the last year of his life was spent in a care center as symptoms of dementia began to overpower him. even still, he continued to carry around his “big silver book” teaching as many as he could about the wonders of the vertebrate fossil record. he was a wonder to the staff and visitors at the home. bob’s passion for science, and more specifically for palaeontology, began, as many such stories do, when he was a small boy growing up on a farm near lansing, michigan. from the address bob gave in 2004 when he was awarded the romer–simpson medal, he was five years old when his father gave him a small collection of fossils from a high school science kit – the bait was on the hook! this first introduction to palaeontology was followed by his father writing to edwin colbert about bob’s passion and colbert responding by sending eight year-old bob an allosaurus femur for a christmas present. to make sure the hook was well set, bob and his dad spent several summer holidays fossil hunting in the green river formation of wyoming, and the white river badlands of south dakota, all before bob was twelve years old. by the time he was a teenager, he had a vast fossil collection in the family barn that he had dubbed “the mason museum of natural history.” after receiving his bsc in geology at michigan state university in 1959 he went on to harvard and the supervision of al romer for his phd (1962) (fig.1). bob was al’s last student and under romer’s mentorship, bob learned to work independently – a mentorship style that deeply influenced his future supervision of his own students. his doctoral dissertation at harvard examined dissorophid amphibians and so began his lifelong quest to understand the evolution of palaeozoic amphibians and the origin of extant amphibians. bob was deeply influenced by romer and romer’s contemporaries, including george simpson and ned colbert, to name just a few, and other harvard luminaries at the museum of comparative zoology (ernst mayr and harry whittington). but romer’s influence was no doubt felt most keenly and personally as bob emulated romer’s focus on comparative anatomy and vertebrate biology. bob’s dive into the biological aspects of palaeontology were as he told the story, driven by his irritation with courses in optical mineralogy – that he hated! as his career progressed, he also picked up romer’s torch so to speak, and accepted the challenge of writing textbooks. bob dedicated years of his life to writing his own version of a comprehensive ‘bible’ of vertebrate palaeontology that remains, after more than thirty years, the standard in our robert “bob” lynn carroll (1938 – 2020) the ‘academic ancestor’ of canadian vertebrate palaeontology michael w. caldwell1 and hans c.e. larsson2 1department of biological sciences, university of alberta, edmonton, ab, t6g 2e9, canada; mikec@ualberta.ca 2redpath museum, mcgill university, 859 sherbrooke street west, montreal, qc, h3a 0c4, canada; hans.ce.larsson@mcgill.ca both authors contributed equally; author order is alphabetical published may 4, 2020 © 2020 by the authors submitted april 27, 2020; accepted april 30, 2020. this article is a tribute and therefore is not peer-reviewed. handling editor: alison murray. doi 10.18435/vamp29364 vertebrate anatomy morphology palaeontology 8:1-6 2 figure 1. bob carroll through the ages. a young bob with his advisor, al romer, in the early 1960s (photo credit unknown); as a young professor in 1975 (photo by phil currie); accepting the romer-simpson medal at the 2004 annual meeting of the society of vertebrate paleontology (photo by richard pierce); and in 2019 (photo by viki doucette). caldwell and larsson — robert carroll 1938–2020 3 pr oo f field. he is perhaps most famous for this text that everyone knows as bob’s ‘big silver book.’ after completing his phd in 1962, bob told the story that professor romer had suggested to him that a good postdoctoral project might include the carboniferousaged tetrapod fossils from nova scotia that were housed at the redpath museum, mcgill university, in montreal, canada. and so bob went to montreal and spent the first year of his postdoctoral fellowship (1962–1963) at the redpath; the second year was dedicated to collections at the natural history museum in london. he had impressed the redpath museum director so much during his year of studies that she invited him to return to montreal to take up a permanent position in 1964 as a professor and curator of vertebrate palaeontology; as we all know, he remained there for the next 56 years. bob’s kindness, drive, mentorship, scholarship, and personality, propelled him to the pinnacle of his profession. his influence can be easily assessed by the usual objective measures – he published literally hundreds of peer-reviewed papers. he wrote several books: vertebrate paleontology and evolution (1988); patterns and processes of vertebrate evolution (1997); the rise of amphibians: 365 million years of evolution (2009); and co-authored paleontology: the record of life (1998) with colin stern. he served as the president of the society of vertebrate paleontology, 19821983, was appointed as strathcona professor of biology at mcgill in 1987, was director of the redpath museum (1985–1991), and chair of the department of biology (1990–1995). he was awarded the schuchert award of the paleontological society (1978), the elkanah billings medal of the geological association of canada (1991), became a fellow of the royal society of canada (1993), won the willet g. miller medal of the royal society of canada (2001), was made an honorary member of the society of vertebrate paleontology (2001), and won the romer-simpson medal from the society of vertebrate paleontology in 2004. his final honor was his appointment to the order of canada in 2019 for “...academic leadership and contributions to his field as canada’s preeminent vertebrate paleontologist.” but perhaps most importantly, he served as supervisor, friend, and research mentor to a large and successful group of palaeontologists, and was himself the academic descendant of an august lineage of scholars (see figure 2, and for a complete list, see below). through bob’s 57–year career at mcgill, perhaps his greatest legacy is that he almost single-handedly created the late 20th and early 21st centuries cohort of canadian vertebrate palaeontologists. in turn, each of these ‘students of bob’ went on to build on his mentorship style and academic legacy by training dozens of other young academics, creating the journal in which this obituary is published, as well as creating the canadian society of vertebrate palaeontology. the stories of bob the academic, scientist, lecturer, and mentor are legion and thus are too many to tell here. nevertheless, we have tried to collect a few of them here so as to share the bob we knew with all of you who might not have known him as we did. in his way, bob was a shy person, particularly in his early days as a young professor. robert reisz, bob’s first graduate student, remembers bob’s lectures on vertebrate palaeontology – “when i took his course in 1968, he was beardless, and looked younger than most of the students. he was quite shy at this early stage of his career, he rarely faced the class and tended to face the blackboard and talked to it. he had all his lectures typed out word for word, but did not read them. instead, i heard him practice his lecture in his office, reading his lecture notes aloud.” while bob’s lecture style never really changed – he seldom looked directly at his audience of students, he did cease rehearsing his lectures and stepped away from his shy, young, student self. his wife anna credits her influence, and we all agree. for years she carried around in her purse two photographs one, the clean cut middle aged bob who wrote the silver book, what she called, “bob after anna”; and the second, a young bob with a civil war era beard, or what she called, “bob before anna”. bob never disagreed on how profound the improvement had been (see figure 1). michael caldwell will never be able to, in fact, is unable to forget, the t-shirt bob wore round the redpath museum, shortly after he and anna returned from a winter holiday to central america – a black t-shirt emblazoned with a dozen pairs of colorful poison dart frogs amplexing in various positions, or as the t-shirt was proudly titled, ‘the kamasutra of frogs’. from robert reisz’s shy young professor, to the not so shy senior professor and fellow of the royal society of canada – bob carroll had clearly ‘evolved’. bob, closely supported by the skillful and artistic efforts of his longtime technician pamela gaskill, emphasized the detailed preparation and illustration of specimens, followed by exacting descriptions of the anatomy of fossil and living vertebrates. he expected no less of his students – his longtime colleague and close friend don baird once accused him of running an art school! daily life in the grad student lab in the basement of the redpath museum was marked by numerous visits from bob...daily visits. and it was always clear when he was on his way as he would come thundering down the 18 stairs to the redpath basement in literally six pounding jumps he had no patience for the one stair at a time approach. he would rush into the grad student room, always excited, a new fossil in hand, or perhaps an old one immortalized in red latex, an old paper, a new paper, or a letter (yes, a paper letter!), to engage the students, question them, argue with them, but always to vertebrate anatomy morphology palaeontology 8:1-6 4 figure 2. a romerogram of bob carroll’s academic genealogy. the academic ancestry and descendants of bob are illustrated in a method introduced by al romer to depict phylogenies through time and bob’s preferred method to illustrate evolution in the fossil record. note the comparably large academic radiation bob founded. academic ancestral names are listed at the times of their doctorate graduations and descendants with ranges spanning from their doctoral graduation to their academic productivity. caldwell and larsson — robert carroll 1938–2020 5 pr oo f learn from and with them. bob never once demanded that the students agree with him, only that each and every one of them could defend their point of view to the best of the data and method at their disposal, whatever that might be. he read your submitted work quickly, was a keen editor, and loved his red pens and pencils, and in the early days, his coloured draft paper. rob holmes still has the marked first draft, on pale yellow paper, of his very first manuscript, covered in bob’s scribbles as together they began the process of revisions. he would read your work again and again until it was ready for submission. michael caldwell fondly recalls bob’s comments at his ph.d. defense, “michael was an excellent student who could not write the english language when he arrived at mcgill. i read and edited an inordinate number of drafts of his first published paper, chapter 2 in his thesis i believe it was 11.” bob pushed evolution in everything he taught and in everything he wrote. evolution was at the center of every excited conversation ever held with his students. he was not a “cladist” as he put it, and never agreed that reducing anatomy to characters assessed by computer algorithms got you anywhere at all. he never pushed his perspectives in print, but yet was always quick to argue his point at great length in conversation with his graduate students, all the while knowing full well that cladograms would appear in our theses and publications. alison murray recalls how bob reacted with glee to the tree statistics in her thesis, delighted that they showed how poorly supported the relationships were, and excited at the thought that he could use similar statistics to show lack of support in published trees of early amphibians. jason anderson cherishes his copy of the lepospondyl volume of the handbook of paleoherpetology that bob signed to him with the statement, “in the hopes for the perfect cladogram!” as rob holmes recalls, he once overheard him say that “...if you believe in evolution, you have to believe in ancestors, and i’m going to keep looking for them until i drop.” bob was always eager to dive into emerging fields and weave them into his view of evolutionary biology. his patterns and processes of vertebrate evolution book was his call to see evolution as not simply changes to 0’s and 1’s in a large matrix, but rather how large biotic and abiotic factors influence evolutionary change. his early entry into evolutionary developmental biology in the 1990’s kept him immersed in multiple fields. he had a talent for weaving together seemingly disparate disciplines to create a comprehensive view of an evolutionary problem. hans larsson will never forget how bob found a way to link, in a single conversation, everything from hylonomus to the cis-regulation of genes to the racing tides of the bay of fundy. in bob’s mind, these were all equally tied together. he loved to live in his scientific world. as a student, it was impossible to really ask for more in a supervisor. bob’s support was endless, as was his expectation that you would work independently. phil currie completed both an msc and ph.d. under bob’s supervision, though he only spent one year of his ph.d. on mcgill campus as he went to alberta for his first palaeo job at the provincial museum of alberta. when asked about phil’s absence from the second required year of residency, bob simply said “i trust that he will finish okay.” four decades on, phil seems to have turned out “okay” and still seems to be doing alright working independently. bob was right. bob was always available for discussion and advice, but never forced his viewpoint on his students. he always questioned differences in perspectives and hypotheses, but never demanded that the results and conclusions be identical to the ones he thought logical. he was a great scholar and student of science, but also a great champion of the arts and literature, and life outside of the academy. martin brazeau will always cherish the christmas card and gift he got from bob, a coffee table book on monet, signed “martin, not all life is fossils, happy new year, bob.” if immortality can be achieved, it is secured by the things we say, write, and do that remain when we are gone. surely bob’s access to immortality is guaranteed by the scholars he trained and those they have and will train, who will proudly claim to future generations of scholars, that they are a direct descendant of robert lynn carroll that he is their “academic ancestor”. list of academic offspring graduate students robert reisz (msc, 1971; phd, 1975) †malcolm heaton (msc, 1975; phd, 1978) don brinkman (phd, 1979) phil currie (msc, 1975; phd, 1981) robert holmes (msc, 1975; phd, 1982) stephen godfrey (phd, 1984) †carl wellstead (phd, 1985) denis walsh (phd, 1987) xiao-chun wu (phd, 1991) lin kebang (phd, 1992) michael caldwell (phd, 1995) dirk meckert (phd, 1996) victor hugo-reynoso (phd, 1997) jason andersen (phd, 2001) alison murray (phd, 2001) tamsin rothery (phd, 2005) nadia fröbisch (phd, 2008) trond sigurdson (phd, 2010) michael debraga (msc, 1990) ed hitchcock (msc, 1991) catherine boisvert (msc, 2004) vertebrate anatomy morphology palaeontology 8:1-6 6 undergraduate students countless undergraduates were supervised by bob for independent studies projects, but those that continued in the field of palaeontology, comparative morphology, and evolutionary biology include: michel laurin (summer 1986, 1987) hans larsson (bsc, 1994) corwin sullivan (young canada works, summer 1997) campbell rolian (bsc honours, 2000) susanne cote (bsc honours, 2001) martin brazeau (bsc, 2004) postdoctoral fellows and visiting students hans-dieter sues (pdf, 1984–86) pierre-yves gagnier (pdf, 1992–94) gary bernacsek (late 1970’s) josef klembara (late 1970’s) olivier rieppel (1975–76) tim smithson (early 1980’s) david dilkes (mid 1990’s) brownstein rebuttal.indd 68vertebrate anatomy morphology palaeontology 6:68-72 issn 2292-1389 vertebrate anatomy morphology palaeontology is an open access journal http://ejournals.library.ualberta.ca/index.php/vamp article copyright by the author(s). this open access work is distributed under a creative commons attribution 4.0 international (cc by 4.0) license, meaning you must give appropriate credit, provide a link to the license, and indicate if changes were made. you may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use. no additional restrictions — you may not apply legal terms or technological measures that legally restrict others from doing anything the license permits. the arundel clay of maryland is an aptian unit (e.g., lipka et al. 2006) that preserves a diverse assemblage of terrestrial vertebrates (e.g., gilmore 1920; weishampel and young 1996; weishampel et al. 2006). dinosaur clades represented in the arundel clay include the dromaeosauridae, titanosauriformes, carcharodontosauridae, nodosauridae, iguanodontia, ceratopsia, and ornithomimosauria, together comprising one of the most diverse faunas of this group of archosaurus known from the early cretaceous of north america (e.g., weishampel and young 1996; kranz 1998; weishampel 2006). because of its extensiveness, the arundel clay assemblage has the potential to greatly inform models of cretaceous vertebrate biogeography (e.g., weishampel and young 1996; kranz 1998; lipka et al. 2006; weishampel 2006). brownstein (2017) examined new theropod material from the arundel clay and concluded the bones reflected the presence of two distinct ornithomimosaurs in the assemblage. however, mcfeeters et al. (2018) disagreed with four major acts in that paper: (1) the confident assignment of the arundel clay pedal unguals to ornithomimosaurs, (2) the identification of one bone as the manual ungual of an ornithomimosaur, (3) comparisons of the arundel clay humerus to the corresponding element in other ornithomimosaur taxa, and (4) the identification of two distinct morphotypes of ornithomimosaur based on comparisons of the pedal unguals. here, i respond to the arguments made by mcfeeters et al. (2018) regarding these and other points of interest. institutional abbreviations: nhrd-ap, fossil collections of the national and historical resources division archaeology program from dinosaur park, maryland, united states; usnm pal/usnm v, paleontology collections of the national museum of natural history, washington, dc, united states. assignment of the arundel clay pedal unguals to ornithomimosaurs regarding the assignment of the pedal unguals (nhrd-ap 2014.s.195, nhrd-ap 2014.s.197, nhrdap 2014.s.198, nhrd-ap 2016.v.1104, usnm pal 529423, and usnm v6107) to ornithomimosaurs, mcfeeters et al. (2018) cautioned that the features used to assign the unguals to this group in rebuttal of mcfeeters, ryan and cullen, 2018, ‘positional variation in pedal unguals of north american ornithomimids (dinosauria, theropoda): a response to brownstein (2017)’ chase doran brownstein stamford museum, 39 scofieldtown road, stamford, ct 06903, usa; chasethedinosaur@gmail.com published july 16, 2018 © 2018 by the author submitted june 1, 2018; accepted june 5, 2018. this article is part of a comment/response submission and therefore is not peer-reviewed. handling editor: robert holmes. doi 10.18435/vamp29340 abstract: the arundel clay of maryland is among the only early cretaceous terrestrial units known from eastern north america. research on some theropod dinosaur bones from this layer has indicated the presence of two ornithomimosaur taxa in the assemblage. however, a recent paper discussed issues with the definite assignment of any of these unguals to ornithomimosauria and suggested that morphological differences originally interpreted to be indicative of the presence of two ornithomimosaurs could be explained by positional variation. here, i show that substantial evidence persists for the presence of two ornithomimosaurs in the arundel clay assemblage, even considering the recent description of positional variation in ornithomimosaur pedal unguals. furthermore, the argument against the confident assignment of these unguals to ornithomimosaurs is shown to be based on oversimplified comparisons that do not take into account the combination of features in the arundel specimens that allow for their assignment to that clade. although several small points made in the initial paper describing the arundel specimens are incorrect or unsubstantiated, the differences between the maryland unguals are outside the spectrum of positional variation and are indicative of the presence of two ornithomimosaurs in the arundel clay assemblage. brownstein — rebuttal of mcfeeters et al. 2018 69 pr oo f brownstein (2017) were either apparently undiagnostic to ornithomimosauria (i.e., a triangular outline in proximal view) or found in other dinosaur clades (e.g., flattened pedal unguals, presence of a flexor fossa on the ventral surface of each ungual, lack of flexor tubercle on each ungual, straightened ventral edges). however, the validity of this argument relies on oversimplified comparisons of the arundel clay unguals with those of spinosaurids, abelisauroids, and gualicho shinyae (e.g., novas et al. 2005; ibrahim et al. 2014; apesteguía et al. 2016; sereno 2017). in addition to representing theropods much larger than those of the arundel clay material, the flattened unguals of spinosaurids are heavily mediolaterally broadened with a larger flexor fossa that extend to the edges of the ungual and includes multiple large ridges (e.g., novas et al. 2005; ibrahim et al. 2014; maganuco and dal sasso 2018). this contrasts with the condition in the arundel clay unguals, which are mediolaterally compressed and have ventral fossa that are smaller, more localized (i.e., surrounded by bone of the ventral surface) and divided in some specimens by a single ridge (fig. 1b). the pedal unguals from the arundel clay also lack a combination of features found in abelisauroids, namely a triangular portion of raised bone on their ventral surfaces and secondary grooves for the claw sheath that run parallel to the dorsal edge of the ungual along the medial and lateral surfaces (e.g., sereno 2017). although the arundel unguals share with those of noasaurids slight curvature, they differ from that group in possessing localized flexor fossa on their ventral surfaces (e.g., novas et al. 2005; sereno 2017). finally, the arundel clay pedal unguals are much smaller than those of gualicho, are not as recurved as in the unguals of that taxon, and lack any flexor tubercles (e.g., apesteguía et al. 2016). abelisauroids and spinosaurids are currently unknown from the fossil record of north america, which is extensive for medium-sized (>10 kg) and large dinosaurs during the jurassic and cretaceous (e.g., weishampel et al. 2004). thus, it is highly improbable that the arundel clay unguals are representative of any of the theropod groups discussed by mcfeeters et al. (2018). based on a combination of their size, slightly recurved to flattened nature, straightened ventral edges, lack of flexor tubercles, proximoventral edges developed into keels, and the presence of localized, deepened flexor fossa on their ventral surfaces, the unguals are assignable to ornithomimosauria (barsbold and osmólska 1990; makovicky et al., 2004; choiniere et al. 2012). as noted, the assignment of the unguals to ornithomimosaurs among other theropod groups is further supported by the absence in north america of theropods that possess unguals morphologically similar in some ways to those of ornithomimosaurs. identification of one bone as the manual ungual of an ornithomimosaur concerning the forelimb elements described by brownstein (2017), mcfeeters et al. (2018) disputed the identification of the bone nhrd-ap 2014.s.196 as a manual ungual. contra mcfeeters et al. (2018), a reduced or nearly absent flexor tubercle is found in ornithomimid manual unguals from the third and fourth digits of the manus (e.g., osborn 1921; osmólska et al. 1972; makovicky et al. 2004). although an interpretation of nhrd-ap 2014.s.196 as an eroded pedal ungual (with the flexor fossa on the ventral surface absent due to erosion) is certainly plausible, the curvature and relative mediolateral compression compared to the ornithomimosaur pedal unguals from the arundel clay support the hypothesis that the specimen comes from the manus rather than the pes (e.g., osmólska et al. 1972; makovicky et al. 2004). a reduced flexor tubercle in this specimen may have been eroded away, as the bone is clearly somewhat abraded (brownstein 2017:fig. 2a-d). the arundel clay humerus compared to that of other ornithomimosaur taxa mcfeeters et al. (2018) also disputed the interpretation of the partial humerus described by brownstein (2017) as of similar robust grade to the corresponding bone in harpymimus based on the incompleteness of the maryland specimen, suggesting that the robust aspect of basal ornithomimosaur humeri previously described could not be determined in the arundel clay specimen. although mcfeeters et al. (2018) are certainly correct that the complete length of the arundel clay humerus is unknown, the size of the distal condyles relative to the proximal end and the thickened, robust nature of the bone in medial and lateral views can all be determined from the bone as preserved (brownstein 2017:fig. 1) and compare favorably to h. okladnikovi (barsbold and perle 1984; kobayashi and barsbold, 2005). identification of two distinct morphotypes of ornithomimosaur in the arundel clay the most extensive critique of brownstein (2017) by mcfeeters et al. (2018) concerned the issue of variation in the unguals of ornithomimosaurs due to their position on the foot rather than to their affinities to multiple taxa. several issues confound the argument of mcfeeters et al. (2018) that differences between the unguals of different digits in the pes account for variation in the arundel clay specimens. mcfeeters et al. (2018) identified five morphological differences among pedal unguals from the same foot in ornithomimids: the outline of the proximal articular facet, the relative sizes of concavities present in this vertebrate anatomy morphology palaeontology 6:68-72 70 facet, the symmetry of the grooves for the claw sheath, the mediolateral curvature of the unguals, and their shape in ventral view; they suggested that these accounted for the differences noted by brownstein (2017) for the unguals described from the arundel clay. however, only two of the features noted by mcfeeters et al. (2018) to vary in ornithomimid unguals known to be from the foot of the same individual correspond to those used to differentiate the unguals from the arundel clay by brownstein (2017): the shape of the grooves for the claw sheath and the proximal articular facet. furthermore, despite the claims of mcfeeters et al. (2018) that the different contributions of the proximodorsal process to the shape of the proximal articular facets in the arundel clay unguals are due to the presence of deepened sulci proximally adjacent to the grooves for the claw sheath on both the medial and lateral surfaces of nhrd-ap 2014.s.195 and usnm pal 529423 and the relative depth of the medial and lateral grooves for the claw sheath are consistent with positional variation, the differences in these features among the arundel clay bones as described by brownstein (2017) either pertain to characteristics that mcfeeters et al. (2018:63) considered uninformative for the position of the unguals in the foot (i.e., “the development of the proximodorsal process”) or differ from the positional variation described in that study (e.g., the deepness of the grooves for the claw sheath). regarding the shape of the proximal articular facet, the variation in the arundel clay unguals is due to the contribution of the proximodorsal process to the shape of the bone, as noted in brownstein (2017), and not to any asymmetrical morphology. in nhrdap 2014.s.195 and usnm pal 529423, the unguals of one morphotype, the proximodorsal process is shortened. however, it is distinctly pinched off from the main bone in proximal view. mcfeeters et al. (2018) claim that the sulci present in nhrd-ap 2014.s.195 and usnm pal 529423 among the arundel clay unguals contribute to their shape in proximal view and use this interpretation to support their argument that the arundel clay unguals represent positional variation in a single ornithomimosaur taxon. however, this is an incorrect interpretation of the anatomy of these specimens. brownstein (2017) noted that the sulci contribute to the ridge on the dorsal surface of nhrd-ap 2014.s.195 and usnm pal 529423 that becomes the proximodorsal process proximally. however, these sulci are separated from the proximal articular facets in nhrd-ap 2014.s.195 and usnm pal 529423 by an area of bone (fig. 1a; brownstein, 2017:figs. 3c, h), and thus do not contribute to the proximal shape of these specimens. the condition in nhrd-ap 2014.s.195 and usnm pal 529423 is unlike that in nhrd-ap 2014.s.197 and nhrd-ap 2014.s.198 (the most well-preserved unguals of the “blunt” morphotype), where enlarged sulci proximal to the grooves for the claw sheath are absent and a more heavily developed proximodorsal process in lateral and medial views does not distinctly diverge from the smooth outline of the ungual in proximal view. whereas mcfeeters et al. (2018) note that asymmetrically deepened grooves for the claw sheath are diagnostic of pedal unguals ii and iv in many ornithomimosaurs from western north america and elsewhere (e.g., in aepyornithomimus, tsogtbaatar et al. 2017) the condition noted by brownstein (2017) to distinguish the two arundel clay ungual morphotypes was that in nhrd-ap 2014.s.198 and possibly nhrd-ap 2014.s.197, both the lateral and medial grooves for the claw sheath are reduced (brownstein, 2017:figs. 4a–b, f–g). in addition to the greater curvature of the unguals nhrd-ap 2014.s.197 and nhrd-ap 2014.s.198 than in nhrd-ap 2014.s.195 and usnm pal 529423 (fig. 1a, d), the different position of the flexor fossa in either morphotype, and the lack of any ridge (= striations of brownstein, 2017) dividing the flexor fossa of the former two bones, these features of the proximodorsal process, proximal articular facet, and grooves for the claw sheath are outside the range of positional variation documented by mcfeeters et al. (2018) and are thus indicative of the presence of two ornithomimosaurs in the arundel clay. although i concur with mcfeeters et al. (2018) in their assignment of particular pedal unguals described by brownstein (2017) to the marginal or central digits of the foot, their argument regarding the assignment of the arundel clay unguals to different positions in the foot of a single taxon of ornithomimosaur is lacking in anatomical evidence. a comparison of well-preserved ornithomimosaur pedal unguals from the arundel clay assigned to different morphotypes by brownstein (2017) may be found in figure 1. additional comments several other comments by mcfeeters et al. (2018) also warrant reply. mcfeeters et al. (2018) challenge the nature of pedal unguals with triangular proximal articular facets as a diagnostic feature of ornithomimosauria. mcfeeters et al. (2018) remarked on the sparse information on ornithomimosaur pedal ungual morphology present in makovicky et al. (2004) and on the shape of the unguals of gallimimus, ornithomimus, and struthiomimus in proximal view. however, in their discussion of the anatomy of these and other ornithomimosaur taxa, makovicky et al. (2004:146) note that in ornithomimosaurs “the pedal unguals are triangular in cross-section with flat ventral surfaces and without flexor tubercles.” nevertheless, i concur with mcfeeters et al. (2018) that this feature may not be entirely diagnostic of unguals of the group, being positionally varibrownstein — rebuttal of mcfeeters et al. 2018 71 pr oo f able as they describe in western north american ornithomimosaur taxa. this does not affect the assignment of the arundel clay specimens to ornithomimosauria, which is based on a variety of other characteristics. mcfeeters et al. (2018:65) claimed that the proximal surfaces of the pedal unguals of beishanlong were not documented by makovicky et al. (2009) [(“makovicky et al. (2009:fig. 3) figured three pedal unguals of beishanlong grandis, but did not document their shapes in proximal view, and pedal ungual iii is not represented”] and regarded this as an issue in the argument of brownstein (2017) against positional variation as the cause of the differences in the arundel clay unguals. however, makovicky et al. (2009:194–195) explicitly remarked that the “recovered pedal unguals [of beishanlong] are triangular in cross section and bear shallow ventral depressions surrounding the highly reduced flexor tubercle.” mcfeeters et al. (2018) also noted the incompleteness of the pedal unguals of rativates evadens as a confounding factor in the argument made by brownstein (2017) against assignment of the arundel clay unguals to different pedal digits of the same ornithomimosaur. however, based on the same figures in mcfeeters et al. (2016:fig. 11a) suggested by them to show unguals too incomplete for discussion of their similarity in proximal view, enough of the proximal end of pedal ungual iv is preserved to demonstrate it possessed a relatively similar triangular outline to pedal ungual ii. mcfeeters et al. (2018) also briefly remarked on the interpretation of usnm 6107 as a pedal ungual iii by brownstein (2017), suggesting it to be curved in dorsal and ventral views in published figures (e.g., gilmore 1920; serrano-brañas et al. 2016). however, asymmetry in this specimen may be amplified due to erosion, as the ventromedial edge is clearly somewhat abraded and is seen as so in the photographs they referenced (serrano-brañas et al. 2016:fig. 8.2b). finally, mcfeeters et al. (2018) discuss issues with the comparison of the arundel clay ornithomimosaur fauna to that of the yixian formation of china by brownstein (2017), noting jin et al. (2012) recovered both taxa from this formation (hexing and shenzhousaurus) within a polytomy of basal ornithomimosaurs. although i concur here that phylogenetic disparity between these genera does not seem extensive, the coexistence of these two taxa in the yixian formation, even when considered closely related, does resemble the condition in the arundel clay in that two genera coexist. this note on the relationships of the yixian formation ornithomimosaurs does not greatly affect the biogeographic discussion of brownstein (2017). mcfeeters et al. (2018) address positional differences in the unguals of ornithomimosaurs, the presence of which have implications for the identification and taxonomic assessment of material from this clade. however, as discussed herein, the arguments made by mcfeeters et al. (2018) against the interpretations of a theropod humerus and possible manual ungual from the arundel clay, the assignment of ornithomimosaur unguals from that unit to the clade and their assignment to two morphotypes, and discussion of the biogeographic implications of all these bones by brownstein (2017) is unsupported by the anatomy of the arundel clay specimens and the data collected in their paper for western north american ornithomimids or unimportant to the discussions in the earlier study. acknowledgements i thank benjamin miller for access to specimens in his care in the collections of dinosaur park in prince george’s county, maryland. literature cited apesteguía s., n.d. smith, r. juárez valieri, and p.j. makovicky. 2016. an unusual new theropod with a didactyl manus from the upper cretaceous of patagonia, argentina. plos one 11:e0157793. barsbold r., and h. osmólska. 1990. ornithomimosauria; pp. 225–244 in d.b. weishampel, p. dodson, and h. osmólska (eds), the dinosauria. university of california press, berkeley. barsbold r., and a. perle. 1984. on first new find of a primitive orithomimosaur from the cretaceous of the mpr. paleontologicheskii zhurnal 2:121–123. 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all other xiphiid remains fall into the eocene–oligocene genus xiphiorhynchus (fierstine 2006). ten species of xiphiorhynchus have been described from the atlantic and former tethys and paratethys, along with a possible record from antarctica (agassiz 1844; cope 1869; van beneden 1871; woodward 1901; leriche 1909; weiler 1929; fierstine and applegate 1974; fierstine and pfeil 2009). possible pliocene remains from the southeastern pacific (peru) have also been suggested to represent xiphiorhynchus (de muizon and devries 1985). despite this diversity and wide distribution, xiphiorhynchus is poorly understood; five species are known only from holotype fragments, and only a handful of specimens include any postcrania whatsoever; moreover, holotypes for two species are lost (fierstine 2006). a new specimen of xiphiorhynchus cf. x. aegyptiacus (istiophoriformes, xiphioidei, xiphiidae) and billfish diversity in the oligocene of south carolina william n. mccuen1,*, aika s. ishimori1, and robert w. boessenecker1,2 1college of charleston, charleston, sc, 29424, usa; mccuennn@g.cofc.edu; ishimorias@g.cofc.edu; boesseneckerrw@cofc.edu 2university of california museum of paleontology, university of california, berkeley, ca 94720 published 12 july, 2020 *corresponding author. © 2020 by the authors; submitted may 7, 2020; revisions received june 15, 2020; accepted june 18, 2020. handling editor: alison murray. doi 10.18435/vamp29367 abstract: a partial billfish rostrum from the chandler bridge formation (early chattian, oligocene) near ladson, south carolina, u.s.a., is described and identified as xiphiorhynchus cf. x. aegyptiacus. the angle of taper, depth to width ratio of the cross section, and other morphological features (including dorsolateral grooves and a planoconvex cross-section), indicate that this specimen (and an earlier published specimen) is closest in morphology to x. aegyptiacus from the eocene birket qarun and qasr el sagha formations of egypt. this confirms the presence of a second xiphiid in the chandler bridge formation besides the well-documented giant swordfish x. rotundus. this is an unusual example of two xiphiorhynchus species existing in sympatry, and strongly contrasting morphologies and morphometrics may point to niche partitioning between the two forms. the occurrence of specimens strongly resembling x. aegyptiacus in the western atlantic also further substantiates past arguments that easy dispersal across the atlantic was possible for this genus, and, by extension, that it shared the open-sea, migratory epipelagic lifestyle of modern swordfish. moreover, the chandler bridge formation boasts the most diverse billfish assemblage in the world, including xiphiorhynchus cf. x. aegyptiacus, x. rotundus, an early istiophorid, and 4–7 species of blochiid billfish in the genera aglyptorhynchus and cylindracanthus. here we describe a new specimen (ccnhm-4406) of xiphiorhynchus from the upper oligocene chandler bridge formation of south carolina. together with previously published remains, it clarifies the identification of another xiphiid taxon (xiphiorhynchus sp.) in the region, enhancing our knowledge of the family’s history while raising questions about its ecology and evolution. materials and methods identification methods: thanks to compilation of extensive morphometric data on billfish rostra by species, it is possible to identify even very fragmentary rostra. we used the datasets of fierstine and starnes (2005) and fierstine and weems (2009) to evaluate ccnhm-4406 in terms of angle of taper (α, the angle between lateral margins) and cross-sectional depth to width ratio (d/w); ratios involving the complete rostrum could not be used because the distal portion of our specimen is missing. mccuen et al. — xiphiorhynchus sp. from oligocene of usa 99 institutional abbreviations: ccnhm, mace brown museum of natural history, at the college of charleston, charleston, south carolina, usa; chm, charleston museum, charleston, south carolina, usa. systematic paleontology class actinopterygii cope, 1887 division teleostei, müller, 1844 order istiophoriformes betancur-r et al. 2013 suborder xiphioidei rafinesque, 1815 family xiphiidae rafinesque, 1815 subfamily xiphiorhynchinae regan, 1909 genus xiphiorhynchus van beneden, 1871 xiphiorhynchus cf. x. aegyptiacus locality and geological setting: chandler bridge formation, chattian (late oligocene), mckewn subdivision, north charleston, dorchester county, south carolina, u.s.a. the chandler bridge formation is typically 1–1.5 meters thick and exposed in the vicinity of summerville, south carolina. it is an unlithified, noncalcareous, and patchy deposit consisting of four beds: olive phosphatic silt (bed 0), light yellowish brown silty quartz sandstone (bed 1), brown phosphatic sandstone (bed 2), and light olive gray clayey quartz sandstone (bed 3; katuna et al. 1997). deposition of the chandler bridge formation was initiated in a marine shelf environment, transitioning to foreshore and estuarine conditions and then a mixed estuarine/ fluvial environment (katuna et al. 1997). microfossils further support this assessment; marine dinoflagellates are common in the lower beds, only to be replaced by pollen and plant debris in bed 2 (katuna et al. 1997). however, marine vertebrate fossils are common throughout the unit, particularly beds 0–2 (katuna et al. 1997; cicimurri and knight 2009), suggesting continuous marine deposition. the chandler bridge formation unconformably overlies the lower oligocene ashley formation, which represents a deeper water (mid-outer shelf ) environment but bears an essentially similar fossil fauna (fierstine and weems 2009). ccnhm-4406 was collected from an unusual section of the chandler bridge formation exposed within two stormwater pond excavations in the mckewn homes subdividision in ladson, south carolina. this section included a 1 m thick typical section of the chandler bridge formation (including beds 1–2, but lacking beds 0 and 3) overlain by 1–1.5 meters of unconsolidated, massively bedded, fine to very fine grained (and occasionally silty) quartz sand with scattered vertical cylindrical burrows and 1–6 cm diameter discoidal quartz pebbles. this upper sandy unit is in turn overlain by the pleistocene ten mile hill beds (weems and lemon 1984). the upper sandy unit entirely lacks calcareous material like the remaining chandler bridge formation and is decidedly less fossiliferous than typical beds 1–2 at the same locality; however, fossil marine vertebrate taxa typical for the chandler bridge formation occur within this unit, including carcharhinus gibbesi, physogaleus aduncas, hemipristis serra, plinthicus stenodon, rhinoptera sp., cylindracanthus, carolinachelys, and the giant dolphin “genus y” (tab. 1). however, some unusual taxa typical for younger miocene deposits also occur, including teeth resembling galeocerdo ‘casei’, carcharhinus leucas, and eurhinodelphinid and squalodelphinid odontocetes. this upper sandy unit differs from the oligocene– miocene edisto formation and parachucla formation by consisting entirely of clean, quartzose sandstone rather than calcarenite and notably lacks a basal phosphatic bonebed. all oligocene–miocene formations in the charleston embayment are expressed with a basal phosphatic bonebed and disconformity (weems and lemon 1984; weems et al. 2014). instead, bed 2 of the chandler table 1. faunal list for the upper sandy unit of the chandler bridge formation chondrichthyes lamniformes carcharocles angustidens isurus sp. carcharhiniformes carcharhinus gibbesi carcharhinus leucas galeocerdo 'casei' hemipristis serra physogaleus contortus myliobatiformes plinthicus stenodon rhinoptera sp. osteichthyes istiophoriformes cylindracanthus sp. xiphiorhynchus cf. x. aegyptiacus testudines chelonioidea carolinachelys wilsoni aves odontopterygiformes pelagornis sp. suliformes sulidae n. gen. n. sp. cetacea odontoceti agorophius sp. agorophiidae n. gen. (genus y) cf. eurhinodelphinidae cf. squalodelphinidae vertebrate anatomy morphology palaeontology 8:98–104 100 bridge formation smoothly grades into the upper sandy unit without a clear erosional surface mantled with a phosphate pebble and fossil bearing lag deposit like other boundaries. therefore, at present, it is most parsimonious to consider this bed to belong to the chandler bridge formation, which is already known to be heterogeneous with lateral changes in lithology and varies from exposure to exposure by the presence or lack of particular beds (chiefly bed 0 and bed 3; sanders et al. 1982; katuna et al. 1997). at this locality, this upper unit appears to grade laterally into a blueish gray siltstone resembling bed 3 – although we hesitate to identify this upper stratum as bed 3 (or a new bed) for the time being. regardless, this lateral facies change from the upper stratum to bed 3 strongly suggests that the two are equivalent in age. the chandler bridge formation has yielded dinoflagellates corresponding to zones np 24–25 (29.6–23.1 ma) and 87sr/86sr ratios from fossil oysters (bed unknown; 24.7–24.5 ma). in accordance with 87sr/86sr dates of 23.5 ma from the overlying edisto formation, an age of 24.7–23.5 ma is assigned to the chandler bridge formation (boessenecker and fordyce 2016). it is unclear whether these dates apply readily to this upper unit as this layer may be younger than the typical beds. the edisto and parachucla formations do not crop out extensively and are rarely identified in subsurface auger holes (weems et al. 2014), and only one small exposure of each unit is present in the charleston embayment, 20 and 28 km (respectively) due west of this locality. the stratum overlying this upper sandy unit is pleistocene. for the time being, no evidence suggests that this upper unit is younger than oligocene and, pending further study, a latest oligocene age is assigned. we note that matrix associated with two skulls of the archaic dolphin agorophius sp. reported from a nearby exposure (coosaw preserve subdivision) by boessenecker and geisler (2018) match this lithology and reassign the stratum that these specimens were collected from (bed 2) to this upper sandy unit. description: billfish rostra, exemplified by the dramatic ‘sword’ of swordfish, marlin etc., consist of extremely elongate, fused premaxillae that bifurcate posteriorly before meeting the rest of the skull while tapering to a sharp point distally (in istiophorids, but not xiphiids, the prenasals also extend into the rostrum’s proximal portion). hollow longitudinal nutrient canals also run the length of a xiphioid rostrum, the number and arrangement of which varies among species and families (fierstine 2006). ccnhm-4406 (fig. 1a–c; tab. 2) is a partial rostrum, acutely triangular in dorsal and ventral views, approximately 11.5 cm long. the cleft between the posterior ends of the premaxillae (where they diverge proximally) is wider and extends farther forward on the ventral side than the dorsal side. on both sides, the cleft extends farther anteriorly along the midline as a shallow groove, with the groove on the dorsal surface deeper than on the ventral side. both grooves gradually shallow and terminate before reaching the distal end of the specimen. breakage at both ends of the specimen reveals the longitudinal nutrient canals typical for billfish rostra (fierstine and voight 1996), but their full number and pattern are not evident, seemingly owing to suboptimal preservation and the natural obscurity of some canals that occurs in some specimens (compare cross sections from fierstine and weems 2009:figs. 25d, e, 26d; fierstine and starnes 2005:fig. 4). almost the entire dorsal and lateral portions have been broken off the hollow proximal section of the right premaxilla. on the left side, enough of the dorsolateral surface is preserved that a wide, shallow groove that reaches to the anterior tip of the fossil is apparent. the ventral surface is much more flattened than the dorsal, giving a planoconvex cross-section (fig. 1d). ccnhm-4406 was found to have an ⍺-value of 10.3°, and a d/w value of 0.53 (tab. 2). identification and comparisons: despite including most of the proximal portion of the rostrum, ccnhm-4406 shows no suturing to indicate extension of the prenasals into the posterior half of the rostrum (characteristic of istiophoridae, see above, fierstine 2006). it also table 2. mean angle of taper (⍺) and depth to width (d/w) ratios of specimens of xiphiodei after fierstine and voigt (1996) and fierstine and starnes (2005), with measurements for ccnhm-4406. (⍺ values for extant species are unpublished and unavailable.) specimen type d/w ⍺ ccnhm-4406 xiphiorhynchus cf. x. aegyptiacus 0.53 10.3 x. aegyptiacus 0.45 11.5 x. eocaenicus 0.62 16.0 x. elegans 0.63 5.0 x. kimblalocki 0.82 10.0 x. rotundus 0.84 19.0 x. priscus (range) 0.69–0.79 3.0–12.0 chm pv8317 (xiphiorhynchus indet.) 0.45 10.5 istiophorus platypterus (mean and range) 0.68 (0.58–0.78) tetrapturus albidus (mean and range) 0.62(0.56–0.66) makaira nigricans (mean and range) 0.70 (0.59–0.80) xiphias gladius (mean and range) 0.34 (0.29–0.39) mccuen et al. — xiphiorhynchus sp. from oligocene of usa 101 figure 1. partial rostrum of xiphiorhynchus sp. cf. x. aegyptiacus (cchm-4406), chandler bridge formation, late oligocene, south carolina. a, dorsal view. b, ventral view. c, left lateral view d, anterior view. e, posterior view. anterior to right for a–c. more clearly visible nutrient canals and the dorsolateral grooving are labelled. vertebrate anatomy morphology palaeontology 8:98–104 102 has a more dorsoventrally flattened cross-section (lower d/w ratio) than the round proportions found in that family, although less flattened than the modern swordfish (xiphias gladius, see table 2). ccnhm-4406 is also distinct from xiphiorhynchus rotundus (d/w = 0.84, ⍺ = 19.0°, see table 2), a xiphiid well-documented from the chandler bridge formation by fierstine and weems (2009). in addition to distinct proportion values, the adult size of x. rotundus (up to around 5 m in total length, based on estimates from isolated vertebrae; fierstine and weems 2009) is also much greater than this individual (although ccnhm-4406 may be a juvenile, considering its small size and relatively poorly ossified, porous bone texture). however, fierstine and weems also reported another, very different specimen of xiphiorhynchus from the chandler bridge, chm pv8317, a rostrum only slightly larger than ccnhm-4406. with a d/w of 0.53 and ⍺ of 10.3°, this specimen not only has similar proportions to ccnhm-4406, it also shares the same planoconvex cross section. they noted close similarity of that specimen in these features to the geochronologically older species xiphiorhynchus aegyptiacus from the late eocene of egypt (tab. 2), but hesitated to refer it to that species owing to poor preservation, difference in time (7–10 my), and geographic separation between localities (fierstine and weems 2009). besides the traits they noted, x. aegyptiacus and chm pv8317 also share a shallow groove on each dorsolateral surface of the rostrum (noted above for ccnhm-4406, compare rostra from fierstine and weems 2009:fig. 26a; fierstine and gingerich 2009:fig. 2b). in view of these similarities, it is likely that chm pv8317 and our specimen, ccnhm-4406, are conspecifics of a poorly understood billfish form from the late oligocene of south carolina, possibly a geochronologically late occurrence of x. aegyptiacus (representing a major range and temporal extension for that species), or an as-yet unnamed close relative. we therefore identify ccnhm-4406 as xiphiorhynchus cf. x. aegyptiacus, noting that more complete specimens are needed to further clarify species-level identification. discussion ecology and distribution of xiphiorhynchus: ccnhm-4406 and chm pv8317 may extend the known geographic and geochronologic range of x. aegyptiacus, raising implications for the ecology of xiphiorhynchus. fierstine and starnes (2005) used the occurrence of xiphiorhynchus sp. cf. x. eocaenicus in north america (x. eocaenicus was previously only documented from britain) to argue for a transatlantic distribution of that species, and, by extension, that species of xiphiorhynchus shared pelagic, migratory cosmopolitan habits with modern swordfish. the presence of x. aegyptiacus in north america would also support this conclusion. however, most xiphiorhynchus species have very limited, rarely overlapping spatiotemporal ranges (agassiz 1844; cope 1869; van beneden 1871; woodward 1901; leriche 1909; weiler 1943; fierstine and applegate 1974; fierstine 2006; fierstine and pfeil 2009; fierstine and weems 2009). this could argue against the south carolina specimens being x. aegpytiacus, but this temporal and spatial restriction very well may be an artifact of taxonomic oversplitting, or the sheer rarity (fierstine 2006) of xiphiorhynchus remains (causing most species to only be known from very few localities). interestingly, xiphiorhynchus aegyptiacus and this extremely similar north american form show some of the lowest known d/w values in the genus, coming closest to those of modern xiphias (tab. 2). this would have affected the function of the rostrum as a hunting weapon, the increasingly popular primary explanation for rostral elongation in xiphioids. rostral morphology and the exact behavioral tactics involved in its employment show variations between extant species (habegger et al. 2015, habegger et al. 2020, hansen et al. 2020). biomechanics studies (habegger et al. 2015, habegger et al. 2020) seem to indicate that rostral flattening in living swordfish helps facilitate rapid lateral slashes to stun or even severely damage small, schooling prey fish, a behavior supported by finds of fish cut in half in swordfish stomachs. the combination of thinness in lateral view with a relatively much greater width would streamline the rostrum for such motion, while still ensuring flexural stiffness, strength against lateral stresses, and a narrow surface of impact for maximum prey damage. in contrast to the more swordfish-like morphology found in x. aegyptiacus, x. rotundus has much higher d/w values, comparable to modern istiophoridae (tab. 2). the same studies on extant billfish rostral function concluded that the round cross-section of istiophorid rostra is better optimized for multi-directional (as opposed to strictly lateral) swiping, as well as stabbing motions. both tactics are supported by field observations of istiophorid hunting and stomach contents (habegger et al. 2015, 2020). considering the role of the rostrum in foraging, it is very possible that the markedly different morphologies in these two forms of xiphiorhynchus reflect differences in hunting tactics as well, perhaps even analogous to those between their modern relatives. billfish ecology and diversity in the oligocene of south carolina: the successive ashley and chandler bridge formations of south carolina represent the richest locality (in terms of diversity) in the world for fossil billfish. besides xiphiorhynchus cf. x. aegyptiacus, and mccuen et al. — xiphiorhynchus sp. from oligocene of usa 103 the giant swordfish xiphiorhynchus rotundus, fierstine and weems (2009) noted that these rocks have yielded at least three (possibly as many as six) species of the large blochiid aglyptorhynchus, the small purported blochiid cylindracanthus, and fragments of the earliest definite istiophorid. the next most speciose billfish assemblage is that of the lower eocene london clay (uk), with six species (friedman et al. 2015). it is unclear whether this unparalleled diversity of fossil billfish reflects time averaging of fossiliferous shallow marine deposits or genuine diversity. in parallel, unusually speciose assemblages of cetaceans and sea turtles (boessenecker and geisler 2018, and references therein; r.w. boessenecker pers. observ.) are reported from these oligocene strata. billfish remains, even if just isolated fin rays, are frequently encountered in the ashley and chandler bridge formations (r.w. boessenecker, pers. observ.), suggesting not just high diversity, but high abundance in the area as well. many of these billfish fossils (for instance, ccnhm-4406) are preserved in shallow marine deposits (see also fierstine and weems 2009), which is contrary to expectations if ancient billfish were deep-water pelagic migrants. however, other authors note that carcasses drifting with the currents, movement of remains long distances in the stomach contents of large predators, and even rostra breaking off in the bodies of impaled animals and being transported thereafter have been observed for modern billfish and cannot be totally discounted for fossils unless they are fairly complete and well-articulated (fierstine and starnes 2005). although time-averaging and even long-distance postmortem transport may help explain billfish richness and diversity in these rocks, other possible factors include niche partitioning or habitat segregation. if postmortem transport was important to ashley and chandler bridge formation taphonomy, it raises the possibility of billfish being transported from slightly different, nearby habitats to a single final resting place. however, particularly if the billfishes of this assemblage shared, at least to some extent, the wide-roaming, epipelagic habits of their modern counterparts, as argued above, it is likely they overlapped and competed directly. in this scenario, fine niche partitioning would explain the diversity observed. against this backdrop, the differences between forms of xiphiorhynchus noted above take on a new interest, as does the bizarre morphology of aglyptorhynchus. unlike any extant billfish, aglyptorhynchus had a mobile rostrum, which, complemented by its equally elongate mandible, would have allowed a uniquely wide gape. moreover, at least one of the species present here, a. robustus, had a ball-and-socket articulation between the first vertebra and the occipital condyle, possibly related to hunting strategy and otherwise almost unknown in teleosts (fierstine and weems 2009). like xiphiorhynchus, the aglyptorhynchus species in this assemblage show variations in rostral morphology (fierstine and weems 2009) that could also have ecological relevance (e.g., higher d/w values in a. palmeri than in a. alsandersi). for now, detailed interpretations of such data must remain speculative, but we hope some of the above points regarding contrasting morphologies may help guide future studies of the factors that have shaped xiphioid diversity. the oligocene rocks of south carolina have proven an excellent source of billfish fossils, outstanding in the world for species richness; future research here promises to continue to clarify the murky evolutionary history of billfishes. acknowledgements this study would not have been possible without the generosity of s. hildenbrandt, who donated the specimen. thanks to b. doster and dr horton construction for locality access. we thank s. boessenecker (ccnhm) for providing access to specimens under her care. finally, we are also grateful to m. manuelo, who was involved in the early research work. literature cited agassiz, l. 1833–1944. recherches sur les poissons fossiles. neuchatel, switzerland: petitpierre. doi 10.5962/bhl.title.4275 betancur-r, r., r.e. broughton, e.o. wiley, k. carpenter, j.a. lópez, c. li, n.i. holcroft, d. arcila, m. sanciangco, j.c. cureton ii, f. zhang, t. buser, m.a. campbell, j.a. ballesteros, 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international (cc by 4.0) license, meaning you must give appropriate credit, provide a link to the license, and indicate if changes were made. you may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use. no additional restrictions — you may not apply legal terms or technological measures that legally restrict others from doing anything the license permits. introduction the ornithomimosaur pes is regarded as an important source of taxonomically informative anatomical information, with several recently named species diagnosed almost exclusively by pedal characters (serrano-brañas et al. 2016; tsogtbaatar et al. 2017; hunt and quinn 2018). most pedal phalanges have distinct morphologies that permit assignment of disarticulated and even isolated elements to their correct position in the pes (e.g., mcfeeters et al. 2016:fig. 11). however, the anatomical differences (here referred to as ‘positional variation’) that distinguish the individual pedal unguals have not been widely appreciated, owing to the relative rarity of ornithomimid specimens that have all three pedal unguals adequately represented, as well as the inaccessibility of some aspects of ungual anatomy in articulated or mounted individuals. published accounts of positional variation in ornithomimosaur pedal unguals are limited in number. one of the few exceptions is tsogtbaatar et al. (2017), in which positional variation in a complete set of unguals from a single pes of the ornithomimid aepyornithomimus tugrikinensis was described and figured. barsbold and osmólska (1990) and makovicky et al. (2004), in their classic overviews of ornithomimosaur anatomy, characterized the morphology of the pedal unguals only in general terms, without discussing positional variation. sereno (2017) identified the single known pedal ungual of a potential basal ornithomimosaur, afromimus tenerensis, as a right pedal ungual ii on the basis of its asymmetry, associated pedal elements, and comparisons to the unguals of a reportedly complete pes of the ornithomimid sinornithomimus dongi. however, as the latter specimen has yet to be figured, this comparison is difficult to evaluate. hunt and quinn (2018) noted positional variation in the incompletely preserved pedal unguals of the basal ornithomimosaur arkansaurus fridayi, but were unable to assign each ungual to a digit. longrich (2008) described some isolated ornithomimosaur unguals, but did not assign them to a particular digit. cullen et al. (2013) described variation in associated ornithomimid unguals with reference to inferred position, and found some of the taxonomic characters used by longrich (2008) to be problematic; however, the unguals described by cullen et al. (2013) were not figured exhaustively, and no rationale for their positional identification was given. positional variation in pedal unguals of north american ornithomimids (dinosauria, theropoda): a response to brownstein (2017) bradley mcfeeters1*, michael j. ryan1,2, and thomas m. cullen3 1dept. earth sciences, carleton university, ottawa, ontario, k1s 5b6, canada; bradleymcfeeters@cmail.carleton.ca 2cleveland museum of natural history, 1 wade oval drive, cleveland, ohio 41106-1767, usa; mryan@cmnh.org 3field museum of natural history, 1400 s lake shore drive, chicago, illinois 60605, usa; thomas.cullen@ fieldmuseum.org *corresponding author published may 24, 2018 © 2018 by the authors submitted april 25, 2017; revisions received may 3, 2018; accepted may 5, 2018. handling editor: robert holmes. doi 10.18435/vamp29283 abstract: positional variation is documented in ornithomimid pedal unguals from the dinosaur park and horseshoe canyon formations of alberta, canada, and characters for identifying the position of isolated ornithomimid pedal unguals are discussed. ungual morphology has been used recently to argue for the coexistence of two distinct ornithomimosaurs, a basal taxon and distinctly more derived taxon, in the early cretaceous arundel clay of maryland, usa. however, these conclusions are based on misconceptions of the morphology and positional variability of ornithomimosaur unguals. some characters previously cited as diagnostic of ornithomimosaur unguals are not actually observed in this clade, or are more homoplastically distributed among theropods. other characters proposed to distinguish between the two pedal ungual morphs in the arundel clay material are shown in the albertan ornithomimid material to consistently distinguish the different ungual positions within the pes of one individual. claims of multiple distinct ornithomimosaur taxa in the arundel clay are premature, as the two pedal ungual morphotypes more likely represent positional variation in a single taxon. mcfeeters et al. — ornithomimid ungual positional variation 61 pr oo f although ornithomimosaurs are well represented in campanian–maastrichtian deposits of the western interior of north america, they are rare in older and more eastern localities on this continent (makovicky et al. 2004) where most reports are based on isolated elements (e.g., schwimmer et al. 2015; brownstein 2017). recently, brownstein (2017) described six isolated ungual phalanges from the aptian-aged arundel clay facies (potomac formation) in maryland, usa, which he regarded as the primary evidence for the existence of two distinct, co-occurring ornithomimosaur taxa in this fossil assemblage (brownstein 2017, 2018). he further suggested that one of these taxa might share a more recent common ancestry with derived ornithomimosaurs such as ornithomimids, than with the other, supposedly more basal ornithomimosaur taxon. brownstein’s interpretation, if correct, has important implications for reconstructing the palaeobiogeographic history of ornithomimosaurs. however, the evidence used to support this conclusion is problematic, being based largely on misconceptions of the morphology and positional variability of ornithomimosaur unguals. in this paper, we re-examine the anatomy of ornithomimosaur pedal unguals from alberta (including material previously described in cullen et al. 2013) with special attention to positional variation among associated elements in an attempt to address this issue. abbreviations institutional abbreviations: amnh, american museum of natural history, new york city, new york, usa; cmn, canadian museum of nature, ottawa, ontario, canada; nhrd-ap, national and historical resources division archaeology program collection at mount calvert historical park, upper marlboro, maryland, usa; rom, royal ontario museum, toronto, ontario, canada; tmp, royal tyrrell museum of palaeontology, drumheller, alberta, canada; ucmz, university of calgary museum of zoology, calgary, alberta, canada; usnm, united states national museum of natural history, washington d.c., usa. anatomical abbreviations: ff, flexor fossa; fo, foramina of flexor fossa; lc; lateral concavity of proximal facet; lg, lateral groove for claw sheath; mc, medial concavity of proximal facet; mg, medial groove for claw sheath; pd, lateral proximal depression; pr, proximodorsal ridge; rc, reconstructed area. descriptions the following description is based primarily on cmn 12068 and cmn 12069 from the dry island ornithomimid bonebed in the tolman member of the horseshoe canyon formation (cullen et al. 2013). these specimens include nearly complete sets of pedal unguals with fully exposed proximal articular facets, permitting rare access to this aspect of their anatomy. due to their close association in a bonebed, these specimens are interpreted as representing the same species, though a precise taxonomic determination has not been reached (cullen et al. 2013). additional supporting observations were taken from the less complete holotypes of struthiomimus altus lambe 1902 (cmn 930) from the belly river group (oldman or dinosaur park formation) near dinosaur provincial park, ornithomimus edmontonicus sternberg 1933 (cmn 8632) from the horsethief member of the horseshoe canyon formation, and rativates evadens mcfeeters et al. 2016 (rom 1790) from low in the dinosaur park formation. an additional fragmentary ornithomimid specimen, tmp 1991.036.0086 from the belly river group of dinosaur provincial park, also preserves pedal unguals ii, iii, and iv, but none of the proximal facets are complete. based on this material, the following general description of the positional variation in these ornithomimid pedal unguals can be made. pedal ungual ii (fig. 1) is relatively large and distally elongate, with the flexor fossa restricted to the proximal half of the total length. the proximal facet is asymmetrical, with a medial concavity that is larger than the lateral concavity. these concavities are separated by a faint subvertical ridge that leans slightly laterally at its dorsal end, forming an approximately 80–85° angle with the plantar surface of the ungual. the proximal facet is taller than wide (and taller than the proximal facet of ungual iii or iv from the same individual), and varies in shape among the specimens in this sample (for example, being relatively narrow and straightsided in cmn 930, versus proportionately broader and more rounded in cmn 8632). the proximoventral edge is nearly straight in ventral view. in ventral view, the ungual is asymmetrical, with the angle between the proximoventral edge and the ventromedial keel being more nearly perpendicular than the angle between the proximoventral edge and the ventrolateral keel. as a result, the spur formed by the proximal termination of the ventrolateral keel may appear more prominent in ventral view that of the ventromedial keel. the groove for the claw sheath is to some degree more pronounced on the lateral side (strongly asymmetrical in tmp 1991.036.0086, but much less so in cmn 930), and a small, roughened depression is sometimes observed on only the lateral side proximal to the groove (cmn 930, cmn 12069). in cmn 12069, the ventromedial edge is sharper than the ventrolateral edge, but this is not apparent when both edges are well rounded, as in cmn 930. pedal ungual iii (fig. 2) is also elongate, but slightly smaller than pedal ungual ii of the same individual. the vertebrate anatomy morphology palaeontology 6:60-67 62 proximal facet is nearly symmetrical, and is approximately as tall as wide, with the maximum width occurring in the ventral half. the lateral and medial concavities are approximately equal in size, separated by an approximately vertical median ridge. in ventral view, the proximoventral edge is straight with rounded medial and lateral corners. the ventral outline is symmetrical, approximating an isosceles triangle distal to the ventral spurs, with the ventromedial and ventrolateral keels converging distally on the midline. the distance between the ventral spurs and the proximal end is proportionately greater than in ungual ii. in contrast with ungual ii, the lateral and medial grooves for the claw sheath are equally developed. proximal to the grooves, dorsolateral and dorsomedial depressions are present on either side of the midline dorsal ridge. due to the generally symmetrical features of pedal ungual iii, it may not be possible to determine whether an isolated specimen belongs to a left pes or a right pes. pedal ungual iv (fig. 3) is in some of its features a mirror image of pedal ungual ii, but is smaller and less elongate, with the portion distal to the flexor fossa typically not exceeding half of the ungual length. the asymmetrical, subtriangular proximal facet is typically slightly taller than wide, but similar in height to that of ungual iii. the larger lateral concavity of the proximal facet is separated from the smaller medial concavity by a ridge that meets the plantar surface at an approximately 70‒75° angle. the proximal facet is skewed medially, such that the ventral edge of the facet is at an oblique angle to the flattened ventral surface of this element, and the proximodorsal process is approximately dorsal to the ventromedial corner. the proximoventral edge is approximately straight in ventral view, except for the more strongly offset ventromedial corner related to the skewed proximal facet. the ventral outline is asymmetrical, with the angle between the proximoventral edge and the ventrolateral keel being more nearly perpendicular than the angle between the proximoventral edge and the ventromedial keel. related to the less elongate morphology, the angle between the ventrolateral and ventromedial keels is typically apfigure 1. pedal ungual ii of ornithomimids: right pedal ungual ii of cmn 930 (holotype of struthiomimus altus) in a, ventral and b, proximal views. left pedal ungual ii of cmn 930 in c, ventral and d, proximal views. left pedal ungual ii of cmn 8632 (holotype of ornithomimus edmontonicus) in e, ventral and f, proximal views. right pedal ungual ii of cmn 12068 (dry island ornithomimid) in g, ventral and h, proximal views. left pedal ungual ii of cmn 12068 in i, ventral and j, proximal views. left pedal ungual ii of cmn 12069 (dry island ornithomimid) in k, ventral, l, proximal, m, medial, and n, lateral views. right pedal ungual of tmp 1991.036.0086 in o, ventral and p, proximal views. mcfeeters et al. — ornithomimid ungual positional variation 63 pr oo f proximately 30°, versus approximately 25° in unguals ii and iii. in dorsal view, the dorsal ridge is variably curved laterally (most prominently in cmn 12069, and more subtly in cmn 930). the groove for the claw sheath is deeper on the medial side, where it is more fully enclosed in cross-section by the overhanging medial wall of the ungual (fig. 3p). a small, roughened depression is sometimes observed on the medial side proximal to the groove. in cmn 12069 and cmn 8632 the ventromedial edge is more rounded than the ventrolateral edge, whereas in cmn 930 both are rounded. positional variation in ornithomimosaur pedal ungual morphology as described above is summarized in table 1. characters identified as positionally diagnostic are related to the shape of the proximal facet, the relative size and elongation of the ungual, and the symmetry or asymmetry of morphological features, whereas positionally diagnostic variation was not consistently observed in the dorsoventral curvature of the ungual, the development of the proximodorsal process, or the form of the flexor fossa or flexor tubercle. in cmn 930, the flexor fossa of the left pedal ungual ii is shallow and lacks obvious foramina or striations, whereas these features are visible on the right pedal ungual ii, suggesting that they are easily masked by poor preservation. on the basis of the above comparisons, we revise the identification of some elements of the dry island ornithomimid (cullen et al. 2013). the element figured by cullen et al. (2013: fig. 2c) as the right pedal ungual iii of cmn 12068 is actually the right pedal ungual ii, on the basis of its asymmetrical shape matching pedal ungual ii of other specimens (fig. 1g–h). the left pedal ungual ii of cmn 12068 may be represented by a weathered proximal fragment (fig. 1i–j), which was not figured by cullen et al. (2013). although the element figured by cullen et al. (2013: fig. 2c) as the left pedal ungual iii of cmn 12068 appears to possess an asymmetrical proximal facet, this is due to the partial collapse of the bone in this region. nevertheless, the lateral and medial concavities on the proximal facet are of approximately equal width, and the overall ventral outline is symmetrical, confirming its original identification as ungual iii (fig. 2c). the element figured by cullen et al. (2013: fig. 3e) as the partial right pedal ungual iii of cmn 12069 is more likely a partial left pedal ungual iv (fig. 3i), possibly belonging to cmn 12068 (no catalogue number is directly associated with it), on the basis of its asymmetrical shape, abbreviated proportions, flexor fossa and ventral spurs located close to the projected distal tip of the ungual, and the relatively large angle between ventrolateral and ventromedial edges. comments on brownstein (2017) brownstein (2017) recently described isolated ornithomimosaur postcranial elements collected from the early cretaceous arundel clay of maryland. he identified nhrd-ap 2014.s.195, nhrd-ap 2014.s.197, nhrdap 2014.s.198, nhrd-ap 2016.v.1104, and usnm pal 529423 as ornithomimosaur pedal unguals based on the presence of a flexor fossa and relatively straight ventromedial edges forming keels, although in some of these specimens he could not confirm both characters (brownstein 2017: 7). following choiniere et al. (2012), he considered pedal unguals with a flat ventral surface and a flexor fossa to occur uniquely in ornithomimosaurs, but these characters also occur in a large theropod pedal ungual referred to the spinosaurid sigilmassasaurus brevicollis by novas et al. (2005). brownstein (2017:7) cited a “triangular shape in proximal view” as additional support for the referral of nhrd-ap 2014.s.197, nhrd-ap 2014.s.198, and nhrd-ap 2016.v.1104 to ornithomimosauria, claiming that this character was considered a synapomorphy of ornithomimidae by barsbold and osmólska (1990). figure 2. pedal ungual iii of ornithomimids: right pedal ungual iii of cmn 930 (holotype of struthiomimus altus) in a, ventral view (proximal end not preserved). left? pedal ungual iii of cmn 12068 (dry island ornithomimid) in b, ventral and c, proximal views. left? pedal ungual iii of cmn 12069 (dry island ornithomimid) in d, ventral, e, proximal, f, medial, and g, lateral views. pedal ungual iii of tmp 1991.036.0086 in h, ventral and i, proximal views. vertebrate anatomy morphology palaeontology 6:60-67 64 however, no such character actually appears in their diagnosis of that taxon (barsbold and osmólska 1990:239); this character is positionally dependent in the albertan ornithomimids observed in this study (table 1). nevertheless, we tentatively accept an ornithomimosaurian identification for the pedal unguals described by brownstein (2017), as it is consistent with the size and overall morphology of these elements. this identification is further supported by the presence of other potentially ornithomimosaurian material in the arundel clay (gilmore 1920; brownstein 2017). however, we point out that this identification may require future revision or refinement with the recovery of additional arundel clay theropod material, given the homoplastic distribution of traditionally ornithomimosaurian pedal ungual characters (such as reduced ungual recurvature, flat ventral surfaces, and presence of a flexor fossa) among other cretaceous theropods including spinosaurids (novas et al. 2005; ibrahim et al. 2014), noasaurids (sereno 2017), and gualicho shinyae (apesteguía et al. 2016). although brownstein (2017) considered most of the unguals he observed to be ornithomimosaur pedal unguals, he identified one element (nhrd-ap 2014.s.196), which he considered to represent a distinct morphotype, as a manual ungual of a more derived ornithomimosaur based on its ventrally flattened shape and absence of a flexor tubercle. he argued that these features allied this specimen with derived ornithomimosaurs such as gallimimus. however, a distinct flexor tubercle is present on all known ornithomimosaur manual unguals, including those of gallimimus bullatus (osmólska et al. 1972:fig. 14). it is therefore unlikely that nhrd-ap 2014.s.196, which lacks this structure, represents an ornithomimosaur manual ungual. brownstein (2017:11) explicitly rejected positional variation to explain the differences between the two ungual morphotypes that were recognized from the arundel clay, claiming that in “ornithomimosaurs where the proximal faces of more than one pedal ungual is exposed and documented (e.g., beishanlong grandis, rativites [sic] evadens, struthiomimus altus, ornithomimus edmonticus [sic], and figure 3. pedal ungual iv of ornithomimids: right pedal ungual iv of cmn 930 (holotype of struthiomimus altus) in a, ventral and b, proximal views. left pedal ungual iv of cmn 930 in c, ventral and d, proximal views. left pedal ungual iv of cmn 8632 (holotype of ornithomimus edmontonicus) in e, ventral and f, proximal views. right pedal ungual iv of cmn 12068 (dry island ornithomimid) in g, ventral and h, proximal views. left pedal ungual iv of cmn 12068(?) in i, ventral view (proximal end not preserved). left pedal ungual of cmn 12069 in j,ventral, k, proximal, l, medial, and m, lateral views. left pedal ungual of tmp 1991.036.0086 in n, ventral, o, proximal, and p, distal cross-sectional views. mcfeeters et al. — ornithomimid ungual positional variation 65 pr oo fgallimimus bullatus), all pedal unguals are flattened or slightly recurved to a similar degree and share a distinct triangular shape in cross-section (makovicky, kobayashi & currie, 2004; makovicky et al., 2009; mcfeeters et al., 2016).” however, makovicky et al. (2004) did not document the detailed pedal ungual morphology of any specific ornithomimosaur taxon in a manner that would allow positional variation in proximal facet shape, curvature, or cross section to be assessed. makovicky et al. (2009:fig. 3) figured three pedal unguals of beishanlong grandis, but did not document their shapes in proximal view, and pedal ungual iii is not represented. mcfeeters et al. (2016:fig. 11) figured three incomplete pedal unguals of rativates evadens, but of these, only one (pedal ungual ii) has a complete proximal articular facet, another preserves a portion of this facet (pedal ungual iv), and the other does not preserve it at all (pedal ungual iii). the type specimens of struthiomimus altus (cmn 930) and ornithomimus edmontonicus (cmn 8632) also lack a preserved proximal facet for pedal ungual iii, while the proximal views of their pedal unguals ii and iv have not been figured. in other specimens referred to these taxa with multiple pedal unguals preserved (e.g., amnh 5339, rom 851, ucmz 1980.1), the precise shapes and details of the proximal facets cannot be readily documented due to the pedal phalanges being mounted in articulation. osmólska et al. (1972:fig. 17, pl. 49) figured two specimens of g. bullatus with multiple pedal unguals preserved, but also did not document the shapes of the proximal facets. brownstein (2017) also claimed that the differences between the two morphotypes do not represent positional variation because positional variation can be recognized within the morphotype interpreted as the more basal ornithomimosaur taxon in this assemblage. according to brownstein (2017:11), usnm v 6107 (co-type of ornithomimus affinis; gilmore 1920) is “straightened” in ventral view, suggesting its identity to be pedal ungual iii. however, it is evident from published figures (serranobrañas et al. 2016:fig. 8) that usnm v 6107 is asymmetrical in ventral view, similar to other pedal unguals assigned to the blunt ungual morphotype. non-ungual material referred to ornithomimosauria by brownstein (2017) includes the proximal and distal ends of a humerus (nhrd-ap 2015.v.103.9) and a caudal vertebra (nhrd-ap 2016.5.503). brownstein (2017) suggested that the relatively thick humerus supports the presence of a basal ornithomimosaur, similar to harpymimus okladnikovi, in this assemblage. however, as the total length of the humerus cannot be established, it is impossible draw any firm conclusions regarding the robustness of this element as conventionally quantified in phylogenetic analyses of ornithomimosauria (kobayashi and lü 2003: character 24). in summary, we conclude that there is no compelling evidence for the presence of two distinct ornithomimosaur taxa in the arundel clay of maryland. discussion and conclusions a review of pedal anatomy of multiple ornithomimosaur taxa from the late campanian-early maastrichtian of alberta reveals a consistent pattern of pedal ungual positional variation. although our sample is too small to assess quantitatively the effects of individual variation on table 1. generalized description of positional variation in ornithomimid pedal unguals. attribute pedal ungual ii pedal ungual iii pedal ungual iv outline of proximal facet asymmetrical, taller than wide approximately symmetrical asymmetrical, subtriangular medial concavity on larger than lateral concavity approximately equal to lateral smaller than lateral concavity proximal facet concavity inclination of ridge ~80°–85° ~90° ~70°–75° on proximal facet outline in ventral view asymmetrical, elongate approximately symmetrical asymmetrical, abbreviated angle between ventro ~25° ~25° ~30° medial and ventrolateral edges grooves for claw sheath may be more pronounced on approximately equal on lateral more pronounced/enclosed on lateral side and medial sides medial side vertebrate anatomy morphology palaeontology 6:60-67 66 ungual morphology, this variation is consistent with that independently documented in another ornithomimid taxon from the campanian of mongolia (tsogtbaatar et al. 2017). among early cretaceous basal ornithomimosaurs, the pedal unguals are most completely represented in nedcolbertia justinhofmanni (kirkland et al. 1998), nqwebasaurus thwazi (choiniere et al. 2012, sereno 2017), and hexing qingyi (jin et al. 2012). comparative data on positional variation is presently limited in that none of these taxa has multiple pedal unguals figured in proximal or ventral views. however, given the strong similarity in the ventrally flattened form of the pedal unguals, and that the asymmetrical morphology of pedal ungual iv in n. thwazi (choiniere et al. 2012:fig. 14) is essentially consistent with the homologous position in ornithomimids, we believe that our criteria for positional assignment can tentatively be accepted for ornithomimosaurs in general. these observations suggest that, if positional variation is not taken into consideration, taxonomic distinctions on the basis of pedal ungual morphology could be erroneous. for example, the figured pedal unguals chosen by longrich (2008:fig. 12) to represent ornithomimus sp. and struthiomimus sedens are both the left pedal ungual ii, but the element figured to represent s. altus appears to be a pedal ungual iii. thus the figure overemphasizes the morphological difference between s. altus and the other taxa, and could create the mistaken impression that other isolated examples of pedal ungual iii from the campanian of alberta compare most favourably with s. altus, regardless of their actual taxonomic origin. positional variation similar to that observed in the albertan ornithomimids can be recognized in the arundel clay pedal unguals referred to ornithomimosaurs by brownstein (2017). the “blunt morphotype” represented by nhrd-ap 2014.s.197, nhrd-ap 2014.s.198, nhrd-ap 2016.v.1104, and usnm v 6107 (brownstein 2017:11), and interpreted by brownstein (2017) as representing a relatively basal ornithomimosaur, corresponds to the marginal pedal unguals (unguals ii and iv) on the basis of the subtriangular, asymmetrical proximal facet, unequally developed claw sheath grooves, an asymmetrical outline in ventral view, and in some specimens (corresponding to ungual iv), abbreviated proportions and weak lateral curvature. the morphotype represented by nhrdap 2014.s.195 and usnm pal 529423, interpreted by brownstein (2017) as representing a relatively derived ornithomimosaur, corresponds to pedal ungual iii, on the basis of the broad, approximately symmetrical proximal facet, symmetrically developed proximal depressions that contribute to defining the proximodorsal ridge, strongly developed claw sheath grooves on both sides, and a relatively elongate and symmetrical outline in ventral view. a significant difference in dorsoventral curvature is not apparent between the two morphotypes figured by brownstein (2017), and we regard the described differences between the flexor fossae as potentially preservational. thus, we see no reason that these two pedal ungual morphotypes could not represent a single ornithomimosaur taxon, contra brownstein (2017, 2018), and favour this as the most parsimonious interpretation. although the sample size is unfortunately too low to exclude coincidence, the number of specimens assigned to each morphotype by brownstein (2017) is proportional to the numbers of central and marginal pedal unguals in a single ornithomimosaur individual (if pedal digit i is assumed to be absent), as would be expected in a random sampling of isolated unguals from a single taxon. brownstein (2017; 2018) suggested that the co-occurrence of relatively basal and relatively derived ornithomimosaurs in the arundel clay makes this assemblage similar to the yixian formation of china. however, the two yixian ornithomimosaurs, shenzhousaurus orientalis and hexing qingyi, are both plesiomorphic in their possession of dentary teeth (ji et al. 2003; jin et al. 2012), and are recovered together in a polytomy near the base of ornithomimosauria in the phylogenetic analysis by jin et al. (2012). thus, the yixian formation appears to lack “derived ornithomimosaurs.” if the arundel clay material does, indeed, represent a single ornithomimosaur taxon (gilmore 1920), then there is no physical evidence supporting the co-occurrence of relatively basal ornithomimosaurs and more derived ornithomimosaurs (i.e., members of the unnamed deinocheiridae + ornithomimidae clade) at any known fossil locality. however, the oldest fossils suggested to be derived ornithomimosaurs (e.g., kinnareemimus khonkaenensis; buffetaut et al. 2009) likely overlap in time with the fossil record of basal ornithomimosaurs, suggesting that such a co-occurrence could be found in the future. buffetaut et al. (2009) suggested that the co-types of ornithomimus affinis may represent a member of the relatively derived clade, based on the morphology of a partial third metatarsal (usnm 5684), but this has not been tested in a published phylogenetic analysis. more information is needed to establish the phylogenetic position of the arundel clay material in relation to better-known ornithomimosaurs, the global pattern of replacement of basal ornithomimosaurs by derived ornithomimids and deinocheirids, and the origins of multi-taxic ornithomimosaur assemblages in north america. acknowledgements we thank margaret currie, jordan mallon, and kieran shepherd at the cmn, david evans, brian iwama, and kevin seymour at the rom, and don brinkman and brandon strilisky at the tmp for assistance during collection visits. robert holmes, alexander dececchi, and an anonymous reviewer provided constructive criticism of an earlier draft of this paper. mcfeeters et al. — ornithomimid ungual positional variation 67 pr oo f literature cited apesteguía, s., n.d. smith, r. juárez valieri, and p.j. makovicky. 2016. an unusual new theropod with a didactyl manus from the upper cretaceous of patagonia, argentina. plos one 11: e0157793, 1–41. barsbold, r., and h. osmólska. 1990. ornithomimosauria; 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sander et al. 2011; schmidtnielsen 1984). however, it is much harder to estimate body mass of extinct taxa due to a variety of factors including a lack of soft tissues, and taphonomic distortion of bones. a wide range of techniques have been developed to try to solve this conundrum, reviewed comprehensively by brassey (2017) and campione and evans (2020). currently, there are two major categories into which mass estimation techniques fall volumetric mass estimates, that use various constraining the body mass range of anzu wyliei (theropoda: caenagnathidae) using volumetric and extant–scaling methods kyle l. atkins-weltman1*, eric snively2 , and patrick o’connor 3,4 1660 gateway court, apt n2, lawrence, ks, 66049, usa; flarginblarg@gmail.com 2osu college of osteopathic medicine at the cherokee nation, 19500 e. ross street, tahlequah, ok ,74464, usa; eric.snively@okstate.edu 3department of biomedical sciences, 228 irvine hall, ohio university heritage college of osteopathic medicine, athens, oh, 45701, usa; oconnorp@ohio.edu 4ohio center for ecological and evolutionary studies, irvine hall, ohio university, athens, ohio, 45701, usa published september 28, 2021 *corresponding author. © 2021 by the authors; submitted july 8, 2021; revisions received september 7, 2021; accepted september 7, 2021. handling editor: jordan mallon. doi 10.18435/vamp29375 abstract: the ability to accurately and reliably estimate body mass of extinct taxa is a vital tool for interpreting the physiology and even behavior of long-dead animals. for this reason, paleontologists have developed many possible methods of estimating the body mass of extinct animals, with varying degrees of success. these methods can be divided into two main categories: volumetric mass estimation and extant scaling methods. each has advantages and disadvantages, which is why, when possible, it is best to perform both, and compare the results to determine what is most plausible within reason. here we employ volumetric mass estimation (vme) to calculate an approximate body mass for previously described specimens of anzu wyliei from the carnegie museum of natural history. we also use extant scaling methods to try to obtain a reliable mass estimate for this taxon. in addition, we present the first digital life restoration and convex hull of the dinosaur anzu wyliei used for mass estimation purposes. we found that the volumetric mass estimation using our digital model was 216–280 kg, which falls within the range predicted by extant scaling techniques, while the mass estimate using minimum convex hulls was below the predicted range, between 159–199 kg. the vme method for anzu wyliei strongly affirms the predictive utility of extant-based scaling. however, volumetric mass estimates are likely more precise because the models are based on comprehensive specimen anatomy rather than regressions of a phylogenetically comprehensive but disparate sample. ways of estimating body volume and density, and extant scaling methods, which use relationships between measured osteological characters and body mass in modern taxa, and attempt to reconcile these relationships with extinct organisms. each method has advantages and drawbacks, which is why using both can be informative (campione and evans 2020) for identifying potential errors in one method or the other and to provide what may be a more realistic range of values, and for tradeoffs of comparative sample size versus time investment. we wanted to determine whether volumetric mass estimation could create a narrower range of body mass estimates than extant scaling for a taxon such as anzu wyliei based on known specimens, using a class of techniques known vertebrate anatomy morphology palaeontology 9:95–104 96 as volumetric mass estimation (or vme), as well as using expanded extant scaling methods than those used in the original description (lamanna et al. 2014). many different methods have been used to estimate body mass from volume. such methods have included using a scaled-down physical model of the animal of interest (alexander 1985; colbert 1962; gregory 1905), and more recent techniques include 3d mathematical slicing (henderson 1999; snively et al. 2019), photogrammetry and parameterized computer modeling (bates et al. 2009; gunga et al. 2008, 1995; hutchinson et al. 2007), and using minimum convex hulls to wrap around a digitized skeletal frame (brassey and sellers 2014; sellers et al. 2012). see brassey (2017) and campione and evans (2020) for a thorough review of each of these approaches. current published mass estimates for anzu wyliei yield a range of 200‒300 kg (lamanna et al. 2014), based both on femoral circumference (anderson et al. 1985) and femoral length measures (christiansen and fariña 2004; zanno and makovicky 2013). however, since the original publication more refined techniques for estimating body mass using stylopodial circumference have been developed that potentially allow for more rigor and further have the added benefit of yielding confidence ranges even for single-point estimates (campione et al. 2014; campione and evans 2020). such methods also do not resort to using multiple different techniques of mass estimation. here, we derive new, updated mass estimates utilizing extant scaling methods developed by campione et al. (2014) and further refined by campione and evans (2020). we then compare these to volumetric mass estimates obtained by digital scanning of anzu specimens as well as manual digital modeling, similar to procedures presented by romano et al. (2021) for the pareiasaur scutosaurus. furthermore, we estimated the animal’s mass with minimum convex hulling, to see which of the applied methods yielded a range that was more congruent with that generated from the extant scaling method. materials and methods volumetric mass estimation to conduct volumetric mass estimation, multiple elements of the paratype specimen of anzu wyliei (cm 78001) and a second caenagnathid from the hell creek formation (currently being described) were digitized using photogrammetry. digital photographs were captured with a canon eos rebel t3i dslr, with point clouds derived from the photos using agisoft metashape. imperfections in the resulting meshes were corrected manually in zbrush 2020. to minimize unnecessary corrections related to taphonomic distortion, only the more complete and/or better preserved of paired elements was digitized, with the exception of the femur. elements of cm 78001 digitized using photogrammetry included the left ilium, left pubis, right ischium, both femora, left tibia, and right fibula. the elements of the second caenagnathid (cm 96523) that were digitized included the left metatarsal iii and the right metatarsal iv. while not pertaining to anzu wyliei, these elements were scaled to appropriate proportions using data from a currently unpublished specimen (m. lamanna, pers. comm. 2020). 3d scans of a series of presacral vertebrae from both the holotype (cm 78000) and referred specimen (cm 78001) were provided by l. roberts. to surmount time constraints, the rest of the skeleton was not directly digitized using photogrammetry – instead, the remaining elements were manually sculpted using reference images of preserved elements from anterior, posterior, lateral, dorsal, and ventral perspectives. manually sculpted elements included cervical and dorsal ribs, sacral and caudal vertebrae and chevrons, the entire pectoral girdle and forelimbs, and the proximal phalanges and unguals of the pes (fig. 1). an approximate life-restoration of anzu wyliei was first constructed in zbrush 2020 using the skeletal outline drawings created by scott hartman as a starting point, though the tail of the life restoration was straightened to make it easier to match the articulation of the caudal vertebrae once they were digitized. the skeletal reconstruction represents a sufficiently accurate starting point as it was used to illustrate in the original description (lamanna et al. 2014). the digitized skeleton was then placed within this life restoration to mimic the position of the skeleton within the living organism, with corrections made to fit the skeleton where necessary (fig. 2). to reconstruct the major pulmonary tissues, dynamesh spheres were imported into the model space, then manually sculpted using inflate, move, and dynamesh tools to shape into the lungs, trachea, and air sacs (fig. 1). to calculate volume and subsequently body mass, the model was exported to 3ds max 2021, where the volume of the entire life model was calculated in addition to the volume of the lungs and air sacs. the composition, position, and estimated arrangement of lungs and air sacs were constrained using osteological correlates for air sac invasion and placement in theropods (o’connor 2006; sereno et al. 2008; wedel 2006) (fig. 1) – specifically, lungs, cervical and abdominal airs sacs, and pneumatic diverticula (e.g., lateral cervical diverticula) were modeled along the cervical and dorsal vertebral series (benson et al. 2012; o’connor 2006; o’connor and claessens 2005). since there are no well constrained osteological correlates for thoracic and clavicular air sacs, we utilized two calculations of body mass. first, we did a calculation using the most conservative model, with only the cervical air sacs, lungs, abdominal air sacs, and trachea present. second was a more extenatkins-weltman et al. — body mass range of anzu wyliei 97 figure 1. digitized skeleton of anzu wyliei with air sacs (“avian” model). model shown in a, lateral; b, dorsal; c, ventral; d, anterior; and e, posterior views. key: green: cervical air sacs; orange: lungs; blue: abdominal air sacs; purple: thoracic air sacs; aquamarine: clavicular air sacs; pink: trachea. note: clavicular and thoracic air sacs were removed in the more conservative reconstruction. vertebrate anatomy morphology palaeontology 9:95–104 98 figure 2. life restoration of anzu wyliei, with skeleton and air sacs semi-visible through transparency. model shown in a, lateral; b, dorsal; c, ventral; d, anterior; and e, posterior views. lungs and air sacs as in figure 1. atkins-weltman et al. — body mass range of anzu wyliei 99 sive air sac system (an “avian model”) that included both anterior and posterior thoracic air sacs, and a clavicular air sac, as are present in avialae (benson et al. 2012; duncker 1971; o’connor 2004, 2006). in this way we account for the uncertainty in presence or absence of such air sacs, and importantly, determine how modeling them affects our estimate of body mass. since the exact and overall tissue densities of extinct organisms are impossible to calculate with certainty, we used two different values for density of the body excluding pulmonary air space to create an upper and lower bound for the model. the lower bound used an estimated density of 800 kg/m3, as has been applied to large sauropods because the pneumaticity in their bones was assumed to lower their body density (gunga et al. 2008), an issue that has been brought up for highly pneumatic saurischian taxa (benson et al. 2012; brassey and sellers, 2014; campione and evans 2020). however, increasing skeletal pneumaticity does not appear to change the total mass of the bones relative to whole body mass—the skeletons of highly pneumatic birds weigh the same relative to total body mass as less pneumatic birds (martin-silverstone et al. 2015; prange et al. 1979). this could mean that skeletal pneumaticity probably does not directly have an effect on whole body density. the negative relationship between density and body mass in birds is probably related to an increase in size of the air sacs relative to total body volume (s. gutherz pers. comm.). thus, to allow for these uncertainties, we used a value of 1000 kg/m3, which has been used in many previous studies aiming to estimate body mass through volumetric methods (bates et al. 2009; henderson 1999; hutchinson et al. 2007, 2011). the non-respiratory value of 1000 kg/m3 is closer to recent estimates for extant and extinct saurischian dinosaurs (larramendi et al. 2020). since previous researchers have used convex hulling methods to estimate body mass of both extant and extinct taxa (brassey and sellers 2014; sellers et al. 2012), we also used this method with anzu for comparative purposes. to construct minimal convex hulls, first the skeleton was exported from 3ds max into meshlab. the skeleton was divided into multiple segments, each given its own convex hull (fig. 3), with each hull used to estimate volume. because exact scaling parameters did not transfer between programs, the transform:scale:normalize function we employed to scale the skeleton as close as possible to the known actual size of the animal. furthermore, meshlab’s volume output was in cm3, and thus we converted these volumes to m3. the total volumes of all segments (tab. 1) were summed together and multiplied by the two extremes of density used for the manually modeled estimate, to establish a range of body masses. while feathers are known to be present in oviraptorosaurs based on direct preservation (funston and currie 2020; qiang et al. 1998; xu et al. 2010; zhou et al. 2000), in addition to indirect inference based on quill knobs on the ulna (kurzanov 1982), in many extant birds, feathers do not contribute significantly to overall body mass (brassey and sellers 2014; hopps 2002; larramendi et al. 2020; table 1. volumes of the convex hulls used to generate a minimum convex hull estimate of body mass for anzu wyliei. body segment volume (cm3) volume (m3) mass (800 kg/m3 ) mass (1000 kg/m3 ) torso 125274.625 0.125274625 100.2197 kg 125.274625 kg tail 12802.94043 0.01280294 10.24235234 kg 12.80294043 kg skull 10121.46387 0.010121464 8.097171094 kg 10.12146387 kg neck 12408.58691 0.012408587 9.926869531 kg 12.40858691 kg l humerus 797.968811 0.000797969 0.638375049 kg 0.797968811 kg l antebrachium 464.968689 0.000464969 0.371974951 kg 0.464968689 kg l manus 1855.232666 0.001855233 1.484186133 kg 1.855232666 kg r humerus 744.117065 0.000744117 0.595293652 kg 0.744117065 kg r antebrachium 466.130646 0.000466131 0.372904517 kg 0.466130646 kg r manus 4343.450684 0.004343451 3.474760547 kg 4.343450684 kg l stylopod 4343.450684 0.004343451 3.474760547 kg 4.343450684 kg l zeugopod 2814.483398 0.002814483 2.251586718 kg 2.814483398 kg l autopod 7956.745605 0.007956746 6.365396484 kg 7.956745605 kg r stylopod 4343.51416 0.004343514 3.474811328 kg 4.34351416 kg r zeugopod 2792.091309 0.002792091 2.233673047 kg 2.792091309 kg r autopod 7956.643555 0.007956644 6.365314844 kg 7.956643555 kg total 199486.4135 cm3 0.199486413 m3 159.5891308 kg 199.4864135 kg l = left; r = right vertebrate anatomy morphology palaeontology 9:95–104 100 results volumetric mass estimation the volume of the complete life model was 0.30 m3 (tab. 2). the air sac volume differed between a more conservative (i.e., lungs and other pulmonary structures modeled at 0.02 m3) and less conservative (i.e., lungs and other pulmonary structures modeled at 0.03 m3). from these results, the conservative model is heavier at an estimated 224-280 kg, whereas the more speculative model is slightly lighter, ranging from 216–270 kg. minimum convex hulling yielded a volume of 0.199 m3 (tab. 1), with a mass estimate between 159 and 199 kg, depending on which body density value was applied. extant scaling methods because the femoral circumference of cm 78001was not available, we were only able to use femoral circumference of the anzu holotype (cm 78000) for the extant scaling regression. however, while the two differ slightly in size, the difference is slight enough that the obtained femoral circumference is a somewhat reasonable proxy for cm 78001 (m. lamanna, pers. comm. 2021), although see table 3 for comparative measurements. the resulting regression yielded a body mass range of between 202 and 342 kg (fig. 4), whereas the original point estimate based on femoral circumference was 193 kg (lamanna et al. 2014). discussion the results obtained from volumetric mass estimates of anzu wyliei fit within both the original mass range proposed in the original description (lamanna et al. 2014) and that predicted by the corroboration plot using campione’s method (campione et al. 2014; campione and evans 2012). thus, current volumetric mass estimate of 216-280 kg provides a more precise range of body masses for this organism than those that use extant data alone (tab. 2). wecke et al. 2017). in large, extant ratites, feathery integument comprises less than 2% of total body mass (brassey and sellers 2014). for this reason, we decided to construct our volumetric model without feathers, and infer that feathers would add up to an additional 2% to the volumetric body mass estimates reported in this paper. extant scaling methods we provided data on femoral circumference of the holotype anzu wyliei (cm 78000) to dr. n. campione, to use in his body mass regression analyses as has been done in previous works (campione et al. 2014; campione and evans 2020) (fig. 4). we also compared these to the values originally obtained by lamanna et al. (2014), as using femoral length as an estimator could still be useful because actual femoral circumference can be easily distorted by taphonomic factors and be made impossible to measure. figure 3. convex hull model of anzu wyliei. model shown in a, lateral; b, dorsal; c, ventral; d, anterior; and e, posterior views. table 2. mass estimates resulting from different methods of estimation. note the increasing precision relative to earlier studies provided by the results presented herein. further note the discrepancy of the minimum convex hull estimate relative to all other estimates. source: lamanna et al. 2014 nicolás campione this paper this paper estimation type: femoral length log stylopodial circumference vme from digitally vme from minimum regression reconstructed model convex hulls result: 200–300 kg 202–342 kg 216–280 kg 159–199 kg atkins-weltman et al. — body mass range of anzu wyliei 101 we also found that the minimum convex hulling method seems to lead to an underestimation of total body mass in this case, though this could be due to scaling errors when transferring between programs. however, if this is indeed a reflection upon minimum convex hulling as a method, it appears when comparing the convex hull model to the manually sculpted life restoration that much of the missing body mass relates to the extremely low volume of both the forelimbs and hind limbs using the hull approach (figs. 2, 3). the convex hull model does not account for the m. iliotbialis, m. iliofibularis, or many of the other muscles connecting the pelvic bones to the femur, or the m. caudofemoralis spanning between the tail and the thigh. the same is true for many of the muscles in the upper forelimb. this could explain the much lower estimate and suggests that aspects of the convex hull method may make implausible biological assumptions. feathers would add less than 2% (brassey and sellers 2014) to our estimate of the body mass of anzu, regardless of method. moreover, it seems likely that with convex hulling, the choice of which elements to include in a particular convex hull may have a strong influence on the final result. perhaps if the pelvic bones were included in the same hull as the femur, for example, the resulting hull would have added the muscles to the proximal hind limb. yet, even if this change were made, there is still the issue of the incredibly thin zeugopodia of both forelimbs and hind limbs, largely underrepresenting both the gastrocnemius and, to a lesser extent, the antebrachial muscles. however, whereas these areas are clearly given less volume than they would account for in life, both the head and the autopodia of both forelimbs and hind limbs account for a greater volume than they would in life. this is because separate elements are often hulled together since the skull is modeled as a single element despite consisting of an upper and lower jaw (and the mouth being open in articulation), the hull included the gap between the jaws in its total volume which is biologically inaccurate. similarly, since the individual fingers and toes were not added as separate hulls, the generated hull connected them in a single, wide structure (e.g., like a duck’s foot), which is not correct. despite these three areas of greater-than-expected volume, they are not sufficient to balance out the underestimation of volume in other regions, resulting in a lower-than-expected body volume regardless of the density value selected. whereas the volumetric mass estimate using a manually constructed life restoration has worked well to narrow the plausible range of body masses for anzu wyliei, we continue to argue for the use of integrated methods making use of both volumetric and extant scaling methods when possible. figure 4. logistic regression of stylopodial circumference versus body mass in dinosaurs, and residual deviance. red lines represent the upper and lower bounds of the 95% confidence interval. the pink dots represent the upper and lower estimates for cm 78000 based on femoral circumference. gray “x” marks represent other specimens of various taxa used to create the regression. regressions and figure courtesy nicolás campione. vertebrate anatomy morphology palaeontology 9:95–104 102 volumetric body mass is only possible for taxa known from relatively complete remains (campione and evans 2020), which greatly reduces its utility in the vertebrate fossil record because many taxa are known only from incomplete skeletons. furthermore, there are still great unknowns about body density, lung and air sac size and structure, and other soft tissue systems that no doubt convey sources of variation within volumetric mass estimates if not carefully accounted for a priori. this may be done by creating more than one model, to account for differing amounts of soft tissue as has been implemented by some researchers (hutchinson et al. 2011), or as we have done here, simply by using a differing possible body density in the same model. we chose the latter, as the relatively small total volume of the model (0.30 m3) and the sensitivity of the software calculating the volume (± 0.01 m3) meant that it would take the addition or subtraction of an immense amount of extra soft tissue relative to the model size to modify the body mass of the model by more than 10–20 kg in either direction. however, with larger taxa, even seemingly small changes may register due to the larger total volume, and thus, the smaller proportion of total volume 0.01 m3 represents. for this reason, we suggest that anyone attempting to replicate this method with larger taxa should use a lower sensitivity to volume changes, perhaps using this study as an approximation of what proportion of total body volume to use for the sensitivity. for example, for an animal with a body volume of 6.0 m3, the sensitivity would need to be twenty times lower (i.e., ± 0.20 m3). researchers can use this in conjunction with a maximum and minimum body density to create a range of body mass estimates using body volume (campione and evans 2020). we reiterate that table 3. comparative measurements of skeletal elements preserved in both cm 78000 and cm 78001, as reported in lamanna et al. 2014. as reported in the original description, measurements greater than 205 mm were taken with tape measure and are therefore less precise, and provided only to the nearest 5 mm. element/dimension cm 78000 cm 78001 skull and mandible braincase height, occipital condyle midline, dorsoventral 10.4 12.3 width of occipital condyle, transverse 20.9 21.7 height of foramen magnum, dorsoventral 18.0 15.3 width of foramen magnum, transverse 15.1 13.1 femur length, proximodistal 525r 505l, 500r width of proximal end, mediolateral 121.7l*, 127.4r 136.3l, 135.5r width of distal end, mediolateral 94.1l*, 112.4r 110.0r tibia length, proximodistal 660l 595l width of proximal end, mediolateral 93.5l, 101.7r* 86.1l depth of proximal end, anteroposterior 104.6l 88.4l width of distal end, mediolateral 101.7l 110.3l fibula length, proximodistal 585l, 580r 570l width of proximal end, anteroposterior 70.0l, 65.0r 74.7l, 67.9r width of proximal end, mediolateral 29.2l, 27.5r 25.0l, 31.8r astragalocalcaneum length, proximodistal 133.1l*, 141.8*r 220l width across distal condyles, mediolateral 98.5l, 98.0r 109.7l metatarsal v depth of proximal end, anteroposterior 16.0l* 20.7l abbreviations: aofe, antorbital fenestra; l, left; r, right; *, element incomplete, measurement as preserved atkins-weltman et al. — body mass range of anzu wyliei 103 these caveats apply to the precision of the specific software used, which yields lower relative error with larger volumes and greater relative error with smaller volumes. software with greater precision, or consistent relative precision regardless of volume, will yield more equivalent relative precision with large and small volumes. conclusions using carefully sculpted digital models based on actual specimens, along with modeling a range of possible body densities, allows for a more realistic and accurate range of possible body masses than extant scaling alone. however, we note that this is only possible when specimens are sufficiently complete and well-known enough to reliably infer basic soft tissue anatomy, and as such, extant scaling is still critical for providing a bracket of reasonable values against which to compare those estimated by volumetric methods. further, we show that there is a great sensitivity of minimum convex hulling to the selection of elements within the hull, making it difficult to determine reliability on animals with lower estimated body sizes. acknowledgements we would like to thank matt lamanna and ami henrici of the carnegie museum of natural history (pittsburgh, pa, usa) for allowing access to the original anzu wyliei type material, and heinrich mallison for providing advice on photogrammetry. we also thank lucy roberts for providing scans of anzu wyliei presacral vertebrae, evelyn volmer 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depending growth of feathers and feather-free body in modern fast growing meattype chickens. open journal of animal sciences 7:376–392. wedel, m.j. 2006. origin of postcranial skeletal pneumaticity in dinosaurs. integrative zoology 1:80–85. https://doi.org/10.1111/ j.1749-4877.2006.00019.x xu, x., x. zheng, and h. you. 2010. exceptional dinosaur fossils show ontogenetic development of early feathers. nature 464:1338–1341. https://doi.org/10.1038/nature08965 zanno, l.e., and p.j. makovicky. 2013. no evidence for directional evolution of body mass in herbivorous theropod dinosaurs. proceedings of the royal society, biological sciences 280:1–8. zhou, z.-h., x.-l. wang, f.-c. zhang, and x. xu. 2000. important features of caudipteryx evidence from two nearly complete new specimens. vertebrata palasiatica 38:242–254. kellner response to martinsilverstone et al.indd 81vertebrate anatomy morphology palaeontology 3:81–89 issn 2292-1389 vertebrate anatomy morphology palaeontology is an open access journal http://ejournals.library.ualberta.ca/index.php/vamp article copyright by the author(s). this open access work is distributed under a creative commons attribution 4.0 international (cc by 4.0) license, meaning you must give appropriate credit, provide a link to the license, and indicate if changes were made. you may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use. no additional restrictions — you may not apply legal terms or technological measures that legally restrict others from doing anything the license permits. there are well over a thousand specimens of the flying reptile pteranodon or, as i prefer to call it, the pteranodoncomplex (kellner 2010). the material comes from the smoky hill chalk member of the niobrara formation (late coniacian early campanian, hattin 1982) and the sharon springs formation (middle campanian, martin et al. 2007) of the pierre shale group. the temporal range of the pterosaur occurrences in these units certainly extend for over four million years (bennett 1992), particularly if the sharon springs formation is taken into consideration. sadly, there is no accurate stratigraphic data for most fossils (miller 1972, bennett 1994). thus, in some cases, one could end up comparing individuals that have lived millions of years apart, a common situation in paleontological studies (e.g., pinheiro and rodrigues, 2017). known since the latter part of the 19th century, there have been several taxonomic reviews of this pterosaur material, most recognizing multiple species (e.g., eaton 1910, miller 1972, schoch 1984), sometimes even including nyctosaurus, which is nowadays regarded as belonging to a distinct clade (e.g., bennett 1994, kellner 2003, andres et al. 2014). the most comprehensive reviews of the pteranodon-complex were done by bennett (1992, 1993, 1994, 2001), who recognized only two species: pteranodon sternbergi, smaller and restricted to the lower section of the smoky hill chalk member of the niobrara formation, and pteranodon longiceps, larger and occurring in the upper section of the smoky hill chalk member and in the overlying sharon springs formation (bennett 1992, 1994). these did not overlap stratigraphically and, according to bennett (1992), both were sexually dimorphic, an interpretation that he still maintains (bennett and penkalski 2017). among the several specimens of the pteranodon-complex that i have examined, one of the most outstanding is the fairly complete skeleton ualvp 24238 (fig. 1 a), which has been briefly illustrated and referred to pteranodon sternbergi by bennett (1992, 1994, 2001). based on the several morphological differences between ualvp 24238 and the holotype of pteranodon sternbergi (fhsm vp 339, that has been previously referred to the genus geosternbergia by miller 1972, 1978; fig. 1b), i came to a different conclusion, ending up establishing the taxon dawndraco kanzai (kellner 2010). recently, martin-silverstone et al. (2017) disagreed with my interpretation, and reassigned ualvp 24238 to pteranodon sternbergi. due to the importance of this debate for pterosaur research in general, as noted by these authors, i decided to challenge their analysis which shows some misconceptions about pterosaur ontogeny, different interpretation of what was actually said about pteranodon, and contains in some parts indication of circular reasoning. i will not discuss all our divergences, but concentrate on the most significant ones. for clarity, i will avoid using taxonomic names for much of this discussion and will refer to the collection numbers ualvp 24238 for dawndraco kanzai and fhsm vp 339 for geosternbergia sternbergi, regarded by them (and by bennett 1992) as conspecific. as odd as it might sound, there is much agreement between my study (kellner 2010) and the one presented by martin-silverstone et al. (2017), which i will briefly summarize below. we agree that ualvp 24238 is an exceptional specimen, one of the best pteranodontid pterosaurs from north america and that it has always deserved a detailed description. i provided some information about this specimen, mainly focusing on the skull (kellner 2010) and martinsilverstone et al. (2017) followed up with a more detailed account. having said that, i would like to add that much more could be done, including the preparation of the pelvis that could provide interesting points regarding the gender discussion (see appropriate section below). rebuttal of martin-silverstone et al. 2017, ‘reassessment of dawndraco kanzai kellner 2010 and reassignment of the type specimen to pteranodon sternbergi harksen, 1966’ alexander w. a. kellner laboratory of systematics and taphonomy of fossil vertebrates, department of geology and paleontology, museu nacional/ufrj, rio de janeiro, rj, brazil; kellner@mn.ufrj.br published august 11, 2017 © 2017 by the author submitted february 2, 2017; accepted may 8, 2017 this article is part of a comment/response submission and therefore is not peer-reviewed. handling editor: robert holmes doi 10.18435/b54d49 vertebrate anatomy morphology palaeontology 3:81-89 82 dr af t we both acknowledge that there is little stratigraphic data for the pteranodontid material in general. we all note that the majority of the specimens are disarticulated or consist of articulated forelimbs alone, and that they are generally crushed and distorted, despite the fact that the bone surface tends to be well preserved (bennett 1994). we also agree that the frontal crest in ualvp 24238 had a comparatively short base, its anterior margin aligning with the anterior margin of the orbit. during my study, i established that the basal portion of the crest of this specimen was not extended and therefore this individual did not have had a broad crest as the one of fhsm vp 339, but entertained the possibility that this cranial structure could have been much longer, somewhat similar to pteranodon longiceps, which still cannot be ruled out. martinsilverstone et al. (2017) revealed that the reconstruction of the small crest present on the display of this skeleton was made aiming to replicate the information retrieved from the field, something i did not know. if ualvp 24238 had had such a small crest, than it would be even more distinct than i originally anticipated. both studies accept that a premaxillary crest cannot be identified in ualvp 24238 (contra bennett 1992 and bennett and penkalski 2017), although martin-silverstone et al. (2017) mention that the crest might be difficult to recognize. overall, we tend to agree with morphologicaldetails of this material and acknowledge that several cranial and postcranial elements are fused. regarding disagreements, i have organized them in topics as a matter of clarity. male versus female martin-silverstone et al. (2017) have pointed out that ualvp 24238 was identified by bennett (1992) as a male against my deduction that it had been regarded as a female (kellner 2010). in fact, except for a sketch apparently based on two specimens of p. longiceps, bennett (1992) never explicitly identified any pteranodon skull in his drawings as representing a male or a female, including ualvp 24238 and fhsm vp 339. in a recent paper, to which martin-silverstone et al. (2017) had access before it was published, bennett and penkalski (2017) specifically stated that in mature males such as ualvp 24238, the depth of the rostrum was increased by a prominent premaxillary crest. although such a crest cannot be identified in ualvp 24238 (kellner 2010, martin-silverstone et al., 2017) or in the large and potentially male represented by fhsm vp 339, this statement shows that i misinterpreted the information published by bennett (1992). despite some lack of clarity in his illustrations regarding the identification of males and females, bennett (1992) has stated that, besides the pelvis (see comments below), sexual dimorphism in these pterosaurs is revealed by the size and extension of their cranial crest. according to him, males show a large frontal crest with an anteroposterior longer base, while in females this cranial structure would be much smaller, with a comparatively shorter anteroposterior base, what is exactly the condition of ualvp 24238 (fig. 1). he also presented a general reconstruction of a male and a female pteranodon longiceps (bennett 1992, fig. 3), a pattern that is somewhat replicated in the subsequent illustrations of the skulls he choose to figure (bennett 1992, figs. 4 and 5). specifically illustrating “pteranodon” sternbergi, bennett (1992, fig. 5) showed only two skulls of that species: ualvp 24238, reproduced as having a small crest, while fhsm vp 339 was reproduced as having a large crest, what is consistent with the main differences between males and females he discussed in the text. therefore, this invites the interpretation of one being a female and the other a male, as i did (kellner 2010). it is also interesting to mention that figure 1. comparisons of the skulls of ualvp 24238 (holotype of dawndraco kanzai) and fhsm vp 339 (holotype of geosternbergia sternbergi), in lateral view: a, drawing of ualvp 24238; b, outline of fhsm vp 339 (reversed); c, superimposition of ualvp 24238 over fhsm vp 339. in c, orbits and nasoantorbital fenestra were used as landmarks and forced to fit, resulting in an increase of ualvp 24238 in about 26% of its original size. a, after kellner (2010) and b, redrawn from bennett (1994). scale bar of a and b = 500 mm. kellner — rebuttal of martin-silverstone et al., 2017 83 the wingspan of the modal niobrara pterosaur female (bennett 1992: 3.8 m) was quite similar to the wingspan estimated by martin-silverstone et al. (2017) for ualvp 24238 (4 m). i am not aware of any other illustrated skull that might reflect the purported differences in males and females of this species (“p.” sternbergi), something that is expected in a paper describing sexual dimorphism where differences in the cranial crest are argued. in any case, it was not the male or female issue that led me to propose a new taxon for ualvp 24238, but the morphological differences that exist between this specimen and other pteranodontids, including fhsm vp 339 (see below). actually, if i had not been mislead, i would have seriously questioned how two mature males of the same species can show so many morphological differences (see fig. 1), what strengthen the case that they belong to different taxa. still regarding the male versus female debate, martinsilverstone et al. (2017) took note about the bimodal pattern recovered by bennett (1992). however, bimodality alone might not provide definite signal for sexual dimorphism (e.g., olson 1957). recognizing this, bennett (1992) relied on morphology for gender differentiation, in this case mainly the extension of the puboischiadic plate. this notion of sexual dimorphism was than used to interpret the differences in the cranial crest morphology of pterosaurs (bennett 1992). to my knowledge, there are no figured specimens of pteranodon (or related species) combining complete posterior regions of skulls and pelves where argumentation for sexual dimorphism could be made (kellner and tomida 2000). perhaps, further preparation of the pelvic region of ualvp 24238, combined with some alternative ways of assessing the size of the pelvic canal in flattened material (e.g., 3-d reconstruction based on ct-scans) might help in this matter (see discussion in cheng et al. 2017). to further demonstrate difficulties of gender differentiation within pterosaurs, although bennett (1992) considered the possibility that the anhanguerids anhanguera and tropeognathus might represent males and females of the same species, this was latter refuted by both, morphology (kellner and tomida 2000) and phylogeny (kellner 2003, andres et al. 2014). nevertheless, there is some basis for recognizing sexual dimorphism in pterosaurs based on the morphology of their cranial crests. in one of the few pterosaur bonebeds (which include some eggs, demonstrating the likelihood of the presence of females), where different individuals can confidently be assigned to the same species, there are morphological evidences suggesting that the expression of the cranial crests (but not their presence, see cheng et al. 2017) might be sexually dimorphic (wang et al. 2014a). in my opinion, this has still to be demonstrated for pteranodon or pteranodon-like taxa. ontogeny the following question is perhaps the most important issue relating to ualvp 24238: what ontogenetic stage has this individual reached at time of death? there is no question that we still need to learn much more about pterosaur ontogeny, and there might be variations from clade to clade. there are a few points, however, that most “pterosaurologists” would agree: fusion of bones is an important tool to establish if an animal had reached skeletal maturity. martin-silverstone et al. (2017) acknowledge that several bones of ualvp 24238 are fused, including elements of the skull, scapulocoracoid, carpals, dorsal vertebrae forming a notarium, tibiotarsus, and the presence of a synsacrum. however, they regard ualvp 24238 as still being a subadult or not yet fully osteologically mature. regarding the skull, martin-silverstone et al. (2017) said that crushing is one of the reasons why they were not able to identify sutures, which raises the possibility that some cranial elements might not have been fused in ualvp 24238. however, bone surface is generally well preserved in most pteranodon material (e.g., bennett 1994). except for some areas, this is certainly true for ualvp 24238, particularly above the nasoantorbital fenestra and the anterior part of the orbit, where several bones are located (e.g., bennett 2001). i offer a different explanation for the lack of sutures in the skull: the bones are fused. sub-adults such as the holotype of the large anhanguerid anhanguera piscator (kellner and tomida 2000), show several unfused elements, but this is not the case here. in animals that have reached or are about to reach full osteological maturity, cranial elements are fused (e.g., kellner et al. 2013), and in some cases leave a sulcus behind indicating where a suture might have been located (see premaxilla and frontal in ualvp 24238, kellner 2010). the fusion of cranial elements is regarded as a feature of fully-grown individuals (bennett 1993), as noted by martin-silverstone et al. (2017). to support their claim for a subadult status of ualvp 24238, even after acknowledging that the fusion of cranial elements is indicative of fully-grown individuals, martinsilverstone et al. (2017) pointed out the presence of “minimal but obvious pitting” on the apices of the right radius, ulna and forth metacarpal, suggesting incomplete ossification of the epiphysis. this is an interesting observation that has been used to identify osteologically immature individuals in the past (e.g., bennett 1993). if this is effectively the case (detailed figures would have helped), then it raises another series of questions: why was this “obvious pitting” not found in the first phalanx of the wing fingers (ph1d4), particularly the left one that they claim lacks an extensor tendon process? and what about other bones? vertebrate anatomy morphology palaeontology 3:81-89 84 dr af t a second feature used by the authors to support a subadult status of ualvp 24238 is the apparent lack of the left extensor tendon process (etp). i have examined the published pictures and drawings and wonder if this portion of the left ph1d4 is not hidden by the distal articulation of metacarpal iv, with which it is articulated. oddly, the right ph1d4, that is well exposed, has the etp fused (kellner 2010), also acknowledged by martin-silverstone and colleagues. what do we know about the fusion of the etp and the ph1d4? according to bennett (1993), these bones are among the last to fuse, shortly before the animal reaches skeletal maturity. i have also made similar observations, although other elements fuse at a latter stage (kellner 2015). nevertheless, the fusion of these elements appears to indicate that ualvp 24238 has reached a late ontogenetic stage at time of death. lastly, martin-silverstone et al. (2017) argued that ualvp 24238 had only five vertebrae fused into a notarium, while it is known that pteranodon had six (bennett, 1993). in my notes and recollections of the specimen, i have counted six vertebrae forming the notarium (kellner 2010), with the last one at least starting to fuse with the preceding element (e.g., transverse processes, part of the neural spine). but let´s entertain the possibility of the completely fused elements of the notarium in ualvp 24238 being restricted to five. the number of vertebrae that fuse into a notarium might change throughout ontogeny, but can also potentially represent differences in taxonomy and we cannot confidently assess this possibility in most cases. for example, a specimen of the anhanguerid tropeognathus cf. t. mesembrinus, which has a maximized wingspan of over eight meters, incorporated five dorsal vertebrae into a notarium and is considered to have had reached skeletal maturity, even if some limited further growth might still have had been possible if the animal had not perished (kellner et al. 2013). in my opinion, the osteological features present in ualvp 24238 strongly suggest that it had reached an advanced ontogenetic stage. this seems (and i am very cautious here) also to be the interpretation of bennett and penkalski (2017), since they specifically stated ualvp 24238 as a being a mature specimen, a detail not acknowledged by martin-silverstone et al. (2017). of course, this does not exclude the possibility of limited growth if this particular individual had not become available for fossilization due to some unknown misfortune. lets, however, again entertain the “subadult” or the “at least nearing, but not yet attaining skeletal maturity” hypotheses put forward by martin-silverstone et al. (2017). what do they want to imply? essentially, that ualvp 24238 could have grown substantially more had it not perished. when fully skeletal maturity was reached, it would have had developed a similar large crest and extended rostrum that are present in fhsm vp 339, since they consider them both males of the same species. although there might be some flexibility inherent to the term subadult, generally used when the animal has passed the juvenile period but did not yet fully develop typical adult characteristics that also involves growth, the fusion of several cranial and postcranial elements argues against the possibility of much additional growth of ualvp 24238. furthermore, even taking into consideration the arguments for this specimen not being fully grown, at least for the pteranodon-complex, same-sized individuals might not have had all bones equally fused, with subadults not much smaller than adults (bennett 1993). in the ontogenetic series of the tapejarid caiuajara dobruskii, there is a substantial increase of the cranial crest from juveniles to subadults. but very early on their ontogenetic development there is no significant modification in the basic shape and inclination of this cranial structure (manzig et al 2014). it seems quite unlikely that the crest would develop from the small size present in ualvp 24238 (for all assuming the reconstruction reflects its real shape, as implied by martin-silverstone et al. 2017) into the large structure found in fhsm vp 339, a purported male of the same species (fig. 1 c). to state that the small size of the crest found in ualvp 24238 fits the “growth predictions” for this pterosaur is unsubstantiated and so far undocumented by all evidence published regarding pterosaur cranial osteological and ontogenetic changes that i am aware of. and that includes all papers on the pteranodon-complex. perhaps the authors might like to provide such a model in the future. considering that the ontogenetic status of ualvp 24238 is paramount for the interpretations of martin-silverstone et al. (2017), there is a more precise way to assess the skeletal maturity of this pterosaur: osteohistological sections. there are several studies on fossil bone histology that provided opportunities to assess the ontogenetic status of one individual, even helping with taxonomic decisions (e.g., padian et al. 2004). despite the destructive nature of this kind of analysis (perhaps more easily done now since for some, ualvp 24238 might not represent a distinct species anymore), one could sacrifice a small piece of both first wing phalanges and the right wing metacarpal of this material since they are already broken. midshafts of humeri and femura might even be better, but than, this specimen might turn out to be a new species after all. here is my prediction: osteohistological sections will find lines of arrested growth and at least some indication of an external fundamental system, showing that substantial growth had already ceased, as observed in ontogenetically mature individuals (e.g., kellner et al. 2013). if not, this would not be a waste of good pterosaur bones, but provide a critical view of what fused bones can actually kellner — rebuttal of martin-silverstone et al., 2017 85 tell about ontogeny. by the way, i would be more than happy to team up with anyone that would like to engage in such a study and that might put the question of the ontogenetic status of ualvp 24238 to rest. rostrum the most outstanding morphological feature of ualvp 24238 is the rostrum. it is deep and shows subparallel dorsal and ventral margins. a premaxillary sagittal crest is not present, although there seems to be some hesitation by martin-silverstone et al. (2017). in order to use an empirical measure to assess the extension of the rostrum that could be compared among all pterosaur taxa, i have introduced an index called the rostral value (rv = ros-l/ aen-h). it is defined as the rostral length (ros-l) divided by the height of the anteriormost point of the external naris (or nasoantorbital fenestra aen-h), where ros-l is measured from the anteriormost point of the external naris (or nasoantorbital fenestra) to the tip of the premaxillae, and aen-h is measured perpendicularly from the ventral margin of the skull to the anteriormost point of the external nares (or nasoantorbital fenestra). martin-silverstone et al. (2017) incorrectly regarded this index as being the same as the rostral index of martill and naish (2006). although both indices consider the length of the rostrum, the rostal index measures the total height of the rostrum immediately anterior to the nasoantorbital fenestra (martill and naish 2006). such a measurement is influenced by the presence and dorsal extension of a premaxillary crest, something that i tried to avoid. martin-silverstone et al. (2017) argue that the comparisons between the rostral value of the holotype of pteranodon longiceps (ypm 1177) and ualvp 24238 are “questionable due to the likelihood” that the rostrum in ypm 1177 might not be complete. however, in ypm 1177 (of which the museu nacional has obtained a cast mn 6953), the upper and lower jaws taper and end essentially at the same point. except for, perhaps, the most anterior tip of both jaws, there is no indication that anything was lost. the argument of martin-silverstone et al. (2017) for the incompleteness of this specimen rests solely on the diagnosis of bennett (1994) for pteranodon longiceps, where the upper jaw (premaxillae) is stated to extend beyond the anterior tip of the mandible. one might argue for different reasons why the upper and lower jaws end at the same point in this particular material or even advocate that the comparisons between of ualvp 24238 and the ypm 1177 (the holotype of p. longiceps) might not be valid. but denying a morphological feature present on a specimen due to the fact that it does not conform to somebody’s diagnosis sounds quite odd, or even troubling, an expression martinsilverstone et al. (2017) like to use. it should be noted that all published reconstructions of ualvp 24238 (bennett 1992, 1994, 2001, kellner 2010, martin-silverstone et al. 2017) are in general agreement. although not being complete, the skull fhsm vp 339 was apparently reconstructed following the outline of the specimen when it was collected (miller 1972). despite some caution, this outline is generally accepted as accurate (e.g., harksen 1966, miller 1972, bennett 1992, 1994, 2001, kellner 2010). by superposing both outlines using the orbit and the nasoantorbital fenestra as landmarks, there is little doubt that the rostra of fhsm vp 339 and ualvp 24238 are very distinct (contra martin-silverstone et al. 2017), with the preserved portion of the latter being substantially deeper and more elongate (fig. 1c). the bony part of the rostral portion of fhsm vp 339 that seems the most reliable portion of the upper jaw in the latest reconstruction presented by bennett (1994, fig. 5) also shows this difference. furthermore, there is a distinct difference in the extension of the anterior portion of the crest relative to the orbit in both specimens (fig. 1c). diagnosis martin-silverstone et al. (2017) do an interesting job of discussing all diagnostic features that i have pointed out to distinguish ualvp 24238 from other pterosaurs. i will not go over each one by one, but note that, although recognizing their existence, they have dismissed them by arguing postmortem distortion or incomplete preservation. in other words, the morphological differences are there, but our interpretations of why they are the way they are differ. regarding flattened fossils, essentially all changes in morphology can be dismissed and attributed to taphonomic changes, if one choses to do so. it should be noted, however, that in the pteranodon-complex case, the comparisons were made between pterosaurs that were preserved in the same depositional environment: under low energy and in deep water conditions (bennett 1994). the material in question was compressed in the same way, with the skulls flattened laterally. thus, comparisons were made with specimens that have been preserved under the same taphonomic conditions. although it would be naive not to acknowledge that even in such circumstances differential morphological changes due to preservation are are possible (e.g., elastic as opposed to plastic deformation, skulls compressed over hard parts present on the substrate or over other parts of their skeleton), this does not appear to be the case here. at least at the first order of approximation, it seems not unreasonable to assume that similar changes might have affected skulls that were preserved in a similar way. vertebrate anatomy morphology palaeontology 3:81-89 86 dr af t concerning diagnoses in general, they might change as more information becomes available. martin-silverstone et al. (2017) use the diagnosis presented by bennett (1994) for pteranodon. although i do refer the reader to the discussion presented previously (kellner 2010), just for the sake of argumentation, i will highlight two points regarding the diagnosis employed by them in the taxonomic discussion of ualvp 24238: the presence of a cranial crest made by the frontals directed up and back, and the presence of proximal caudal vertebrae with duplex centra. cranial crests made by the frontals have since been reported in other pterosaurs such as guidraco and ludodactylus (frey et al. 2003, wang et al. 2012) and proximal caudals with duplex centra were reported in anhanguera (kellner & tomida 2000). that said, regarding the cranial crest, a highly controversial topic these days (see cheng et al. 2017), i hardly believe that guidraco or ludodactylus should be classified into the genus pteranodon, but just would like to stress that diagnoses can change with the advent of new specimens or more information. that seems also to be the case for the pteranodon-complex. splitter versus lumper regarding my decision to erect a new species for ualvp 24238, martin-silverstone et al. (2017: p. 47) stated that: “no phylogenetic analysis is presented, and these decisions appear to represent a preference for taxonomic splitting.” they are correct that i did not present any phylogeny regarding my taxonomic decision on uavlp 24238 (neither did they, did they?). taxonomic decisions regarding species do not necessarily need to rest on a phylogenetic analysis, as was also the case for previous taxonomic decisions regarding the specimen discussed here (uavlp 24238) and others of the pteranodon-complex (e.g., bennett 1992, 1994). similarly, a phylogenetic analysis is not necessary when a specimen is assigned to a pre-existing clade (e.g., martin-silverstone et al. 2016). however, from all arguments presented by martinsilverstone and colleagues against my interpretation of ualvp 24238, the most surprising one to me was the splitter label. am i a splitter, perhaps boosting up diversity where there is none? looking back on some of my taxonomic decisions, i was involved with my colleague diogenes campos in a project that has regarded the anhanguerid tropeognathus congeneric with anhanguera (kellner and campos 1988), a decision that proved to be partially correct (kellner and tomida 2000, andres et al. 2014). again with campos, when describing a tapejarid from the early cretaceous crato formation, i initially “lumped” the species now known as tupandactylus imperator (kellner and campos 2007) with the genus tapejara (campos and kellner 1997). not to mention that i went a great length to provide information about some chinese pterosaurs in exactly the same publication where i decided on uavlp 24238, discussing why i agreed that huaxiaperus jii should be synonymized (or “lumped”) with sinopterus dongi (kellner 2010). does this make me a “lumper”, that might not recognize true diversity and unites different species into the same one what has several undesired consequences (e.g., biogeography)? i do not have any particular preference when it comes to taxonomic decisions. i have previously discussed the difficulties of species recognition in pterosaurs (that could be applied to other vertebrates as well), which have resulted in disagreement among researchers (kellner 2010), and i will not repeat it here. as a matter of fact, i do feel that the pterosaur diversity does not suffer from oversplitting, but perhaps rather from overlumping. and this does not reflect any preference of mine. for example, several species previously regarded as belonging to the eudimorphodon-complex (first pointed out by kellner 2003) and pterodactylus of solnhofen are now placed in different genera (e.g., dalla vecchia 2009, vidovic and martill 2017). older collections have been revisited and apparently also show more diversity than originally thought (e.g., hone et al. 2017). and this does not seem to be related to a new and general trend of typological oversplitting. nonetheless, as i have stressed before (kellner 2010), morphology is crucial for establishing or synonymizing species. granted, as happens at present, there should be plenty of individual variation within members of a single species for several reasons (e.g., ontogeny, food resources). it is also possible that pterosaurs (or some of them) showed marked sexual dimorphism that would be expressed not only by the soft tissue morphology (e.g., different colors of pycnofibers, colorful soft tissue extensions on cranial crests), but also in the skeleton. we expect that because it is observed nowadays when studying individuals of populations that can be confidently assigned to the same species. and here resides the problem with pterosaurs (and most other fossil vertebrates): the lack of populations that might reflect the same species in the fossil record! concerning pterosaurs, there are only three bonebeds available (e.g., chiappe et al. 1998, chiappe et al. 2000, codorníu and chiappe 2004), two of which were discovered a few years ago and have not yet been studied in detail (wang et al. 2014a, manzig et al. 2014). all are predominantly monospecific and none shows pterosaur cranial material with so many morphological differences as observed between ualvp 24238 and fhsm vp 339 (fig. 1c). these differences have now even become more significant since apparently sexual dimorphism was ruled out (martinsilverstone et al. 2017, bennett and penkalski 2017). kellner — rebuttal of martin-silverstone et al., 2017 87 regarding stratigraphy, as correctly pointed out by martin-silverstone et al. (2017), i have called attention to the fact that, according to bennett (1994), ualvp 24238 and fhsm vp 339 come from different stratigraphic levels; but this was not the primary justification for the separation of these specimens in different species morphology was. as i have pointed out before (kellner 2010), morphology (m) is the main aspect to be considered, but stratigraphy (s) and, to a lesser extent geography (g), are also part of the equation (msg). bennett (1992) mentioned that the specimens of the pteranodon-complex were collected in deposits formed some 200 km away from the ancient cretaceous shorelines. this potentially could have restricted diversity (i.e., smaller species might not have been able to fly so far away, not considering biostratinomy). even keeping this potential preservation bias in mind, the occurrence of a higher number of flying reptile species in this stratigraphic section is not inconceivable, particularly taking into account that two formations representing over 4 million years, whose outcrops spans over a considerable geographic area, are involved. if one takes the jehol biota of china as an example, although agreeing that the number of species might be inflated (e.g., wang et al. 2005, wang and zhou 2006, kellner 2010, but see andres et al. 2014), there is a tremendous amount of diversity, even if only considering the aptian jiufotang formation (e.g., wang et al. 2005, lü and ji, 2006, lü et al. 2008, wang et al. 2012, wang et al. 2014b, andres et al. 2014). since it seems quite implausible that all these pterosaurs came from the same horizon (no pterosaur bonebed regarding this deposit is known) or represent species that cohabited the same area during the same time, one compelling (but admittedly speculative) explanation that might explain this diversity is that fossils come from different layers. it appears that taphonomic and paleoenvironmental conditions of the jiufotang deposits (and perhaps other similar ones in china) might have resulted in “sampling” of the biota during different times along some million years. however, as with the pteranodon-complex, there is not enough stratigraphic data to support this hypothesis, but the point here is that stratigraphy should not be dismissed a priory and can be argued to back morphology. final comments i do not cherish any illusions that these lines will settle the question regarding the taxonomic status of ualvp 24238 and fhsm vp 339, which i consider to represent distinct taxa, dawndraco kanzai and geosternbergia sternbergi, respectively (kellner 2010). this view is even more strengthened now that sexual dimorphism was apparently excluded. even if ualvp 24238 represents an ontogenetically younger animal then i had thought, there are still lots of differences in morphology that cannot be dismissed by general statements such as “difficult to measure”, “postmortem distortion”, and “incomplete preservation”. this kind of argument can be used for rejecting almost any morphological difference in non-3d specimens. however, contrary to most disputes over taxonomical issues, the present one might be solved quite easily with osteohistological sections. such a study will give us a better understanding of the growth potential that was still left for ualvp 24238 at time of death, shedding some needed light on the “male hypothesis” regarding this specimen. i have not discussed the diversity of cranial material of the pteranodon-complex presently available for study, but based on ualvp 24238 (and another skull, see kellner 2010), i argue that there is more taxonomic diversity than currently admitted by bennett (1994, 2001) and martin-silverstone et al. (2017). if the remarkable variation in cranial morphology presented by these purported males, where the smaller one (ualvp 24238), albeit having reached an advanced ontogenetic state (at least 0s5 of kellner 2015), shows so many differences from the larger (fhsm vp 339) and still both represent the same species, it might just be very hard to tell pterosaurs apart. lastly, i am afraid that achieving a so called “solid foundation of pterosaur science” might, unfortunately, be still some time away. perhaps this may be best accomplished by keeping open-minded about different ideas and try to test them. acknowledgements i wish to thank alison murray for granting the possibility to respond to martin-silverstone et al. (2017) and robert holmes for editorial suggestions. along the years, i profited from several discussions with several colleagues about pterosaur ontogeny and sexual dimorphism too many to list here. founding for my research comes from the conselho nacional de desenvolvimento científico e tecnológico cnpq, (cnpq # 304780/2013-8 and the fundação carlos chagas filho de amparo a pesquisa do estado do rio de janeiro (faperj # e-26/202.893/2015). literature cited andres b., j. clark and x. xu. 2014. the earliest pterodactyloid and the origin of the group. current biology 24:1011‒1016. bennett, s.c. 1992. sexual dimorphism in pteranodon and other pterosaurs, with comments on cranial crests. journal of vertebrate paleontology 12:422–434. doi 10.1080/02724634.1992.10011472 vertebrate anatomy morphology palaeontology 3:81-89 88 dr af t bennett, s.c. 1993. the ontogeny of pteranodon and other pterosaurs. paleobiology 19:92–106. doi 10.1017/ s0094837300012331 bennett, s.c. 1994. taxonomy and 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m.p. witton, and d.m. martill (eds.). new perspectives on pterosaur palaeobiology. geological society special publications 455: https://doi.org/10.1144/sp455.12 wang, x., a.w.a. kellner, s. jiang and x. cheng. 2012. new toothed flying reptile from asia: close similarities between early cretaceous pterosaur faunas from china and brazil. naturwissenschaften, 99:249‒257 (doi 10.1007/s00114-0120889-1). issn 0028-1042. wang, x., a.w.a. kellner, s. jiang, q. wang, y. ma, y. paidoula, x. cheng, t. rodrigues, x. meng, j. zhang, n. li, and z. zhou. 2014a. sexually dimorphic tridimensionally preserved pterosaurs and their eggs from china. current biology 24:1323–1330. doi 10.1016/j.cub.2014.04.054 wang, x., t. rodrigues, t., s. jiang, x. cheng and a.w.a. kellner 2014b. an early cretaceous pterosaur with an unusual mandibular crest from china and a potential novel feeding strategy. scientific reports, 4:6329 (doi: 10.1038/srep06329). wang x. and z.h. zhou. 2006. pterosaur assemblages of the jehol biota and their implication for the early cretaceous pterosaur radiation. geologisches jahrbuch 41:405–418. vertebrate anatomy morphology palaeontology issn 2292-1389 vertebrate anatomy morphology palaeontology is an open access journal http://ejournals.library.ualberta.ca/index.php/vamp article copyright by the author(s). this open access work is distributed under a creative commons attribution 4.0 international (cc by 4.0) license, meaning you must give appropriate credit, provide a link to the license, and indicate if changes were made. you may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use. no additional restrictions — you may not apply legal terms or technological measures that legally restrict others from doing anything the license permits. published 21 may, 2021 editors: alison m. murray, hallie street and robert b. holmes © 2021 by the authors doi 10.18435/vamp29374 meeting logo design: our 2021 meeting logo (front cover) is by matthew rhodes. he says the design is “a tribute to the ‘academic ancestor’ of canadian vertebrate palaeontology, robert “bob” lynn carroll (1938–2020). carroll represents canadian palaeontology not only by his own contributions to the field, but also by the ‘academic radiation’ of his numerous students, many of whom continue to shape the field today. much of carroll’s research was dedicated to early tetrapods, particularly from eastern canada. this led me to his 1969 description of paleothyris, an early reptile often used as a representative of the anapsid skull condition, including in his own book vertebrate paleontology and evolution. the paleothyris climbing through the logo was inspired by figure 12 of carroll (1969), which cuts off around the base of the tail—the same position at which the logo turns into digital blocks. carroll’s works often have romerograms (spindle diagrams), so a maple leaf-shaped one materializing from the v seemed appropriate. on a deeper level, the paleothyris sits at the base of the v as if it was the ancestor of the romerogram’s central branch, echoing one of carroll’s lines quoted in caldwell and larsson (2020) in vamp: “... if you believe in evolution, you have to believe in ancestors, and i’m going to keep looking for them until i drop”. ” canadian society of vertebrate palaeontology 2021 abstracts 3 9th annual meeting canadian society of vertebrate palaeontology may 26–28, 2021 online abstracts vertebrate anatomy morphology palaeontology 9:1–39 4 message from the organizing committee greetings to our members across canada and around the world what kind of year has it been? travel restrictions and work-from-home orders have limited our abilities to meet, use lab facilities, and conduct fieldwork. regardless, vertebrate palaeontology research has adapted and progressed, though maybe in different directions than were anticipated at the beginning of 2020. this year’s annual meeting finds us at a sensitive crossroads during the covid-19 pandemic, balanced between the increasing availability of vaccines and the concerns over the spread of new variants. staying connected and inspired may be particularly important during these uncertain times, and so the society felt it was important to have an annual meeting this year. therefore we are venturing into the realm of digital conferencing. the csvp 2021 meeting will be held on may 26–28th with an introductory guest lecture by dr. grant zazula on may 25th. the oral presentations will be given live using zoom (a video conference software), and digital posters will be available throughout the meeting with a live session for questions and discussions. the virtual organizing committee and the executive committee are aware of just how much of our interactions take place via similar media these days, and so the decision was made to limit the conference to a few hours each afternoon/evening. we hope this makes the annual meeting accessible to all our members without being overwhelming. the reduced time did limit the number of presentations we were able to accept, and so we hope that members of the society understand our choice to prioritize students and early career researchers. there are, of course, aspects of an in-person conference that we cannot replicate virtually. however, without the need to pay for travel or accommodations, the virtual format of csvp 2021 has attracted interest from students and researchers across canada and from as far afield as europe and asia. we are grateful for the dedication, patience, and flexibility the members of our community have shown to each other and to the society over the past fifteen months. we hope members can make the best of the virtual meeting this year, and we look forward to our next opportunity to meet in person, your virtual organizing committee, bassel arnaout emily bamforth julien divay annie mcintosh hallie street yan-yin wang canadian society of vertebrate palaeontology 2021 abstracts 5 table of contents message from the host committee lissamphibia: a polyphyletic group within temnospondyli? thomas arbez ........8 first occurrence of a sea turtle (clade panchelonioidea, superfamily chelonioidea) from the dinosaur park formation of saskatchewan, canada emily l. bamforth and hallie p. street ........9 potential preservation of keratinous tissues associated with frill ornamentation of an immature centrosaurus (ornithischia, ceratopsidae) caleb brown ........10 development and evolution of regionalization within the avian axial column hoai-nam n. bui and hans c.e. larsson ........11 first definitive occurrence of polycotylidae (short-necked plesiosaurians) from non-marine sediments of the dinosaur park formation of alberta: evidence for a multi-taxic, freshwater plesiosaurian assemblage james a. campbell and caleb m. brown ........12 palaeopoems: a digital anthology highlighting a unique form of science communication brigid e. christison, michael g.w. thompson, and katrin emery ........13 evolution of marine ecosystems, a global view from the early cretaceous marine tetrapods of colombia dirley cortés, hans c.e. larsson, erin e. maxwell, alexandre demers-potvin, hoai-nam bui, anthony smith, and mary luz parra-ruge ........14 morphological analysis of a nectridean lepospondyl, diceratosaurus, from linton and five points, ohio jamey h.m. creighton and jason s. anderson ........15 a morphometric analysis of the turtle manus and its implications for the palaeoecology of extinct turtles thomas w. dudgeon, marissa c.h. livius, and jordan c. mallon ........16 a new plastomenine trionychid (testudines: pan-trionychidae) from the milk river formation of southern alberta (cretaceous: santonian) shauna c. edgar, don b. brinkman, michael j. ryan, and david c. evans ........17 life history of an archaic placental mammal, pantolambda bathmodon (placentalia, pantodonta) gregory f. funston, paige e. depolo, sarah l. shelley, john r. wible, thomas e. williamson, and stephen l. brusatte ........17 revisiting the sedimentology and depositional evolution of the cypress hills formation (eocene – miocene) in southwestern saskatchewan, canada: implications for vertebrate microfossil assemblages meagan m. gilbert ........18 dinosaur fossil discovery using remotely piloted aircraft systems and spectral mixture analysis sean herridge-berry, caleb m. brown, derek r. peddle, brian j. pickles, and craig a. coburn ........19 feeding ecology of the bearpaw formation mosasaur community femke m. holwerda ........21 vertebrate anatomy morphology palaeontology 9:1–39 6 osteohistology of a thescelosaurid (dinosauria, ornithischia) fibula from the wapiti formation (campanian) of northern alberta: implications for diversity of growth strategies and osteohistological features within thescelosauridae michael naylor hudgins, phil r. bell, nicolás e. campione, federico fanti, robin l. sissons, matthew j. vavrek, derek w. larson, and corwin sullivan ........22 impacts of miocene tectonism and climate change on diversity dynamics of carnivoran and ungulate mammals in north america blue hunter-moffatt, and danielle fraser ........23 new material of the oldest metamorphic salamander (amphibia, urodela) from the middle jurassic of china yields insights into palaeoecological disparity jia jia, jason s. anderson, and ke-qin gao ........24 vertebrate diversity trends and chrono-, litho-, chemo-, and cyclostratigraphy of the late cretaceous manitoba escarpment in saskatchewan and manitoba, canada aaron a. kilmury, michelle p.b. nicolas, and kirstin s. brink ........25 the internal cranial anatomy of panoplosaurus mirus (dinosauria: nodosauridae) marissa c.h. livius, hillary c. maddin, michael j. ryan, jordan c. mallon ........26 first record of a parasaurolophin hadrosaur from the oldman formation of southern alberta bradley d. mcfeeters, david c. evans, michael j. ryan, and hillary c. maddin ........26 palaeobiodiversity statistics and paleoenvironmental implications of microvertebrate localities from the frenchman formation (latest cretaceous, maastrichtian) of saskatchewan, canada jack r. milligan, and emily l. bamforth ........27 a bird coracoid from the horseshoe canyon formation (earliest maastrichtian) of alberta, canada sydney r. mohr, gregory f. funston, and thomas a. stidham ........28 a quantitative analysis of morphological variation in dentition among thescelosauridae with implications for thescelosaurid palaeoecology, macroevolution, and microsite identification nathaniel e.d. morley, michael naylor hudgins, caleb m. brown, philip j. currie, han feng-lu, and corwin sullivan ........29 new data on the distal tarsals of ornithomimidae provided by a partially articulated specimen from the kaiparowits formation (late campanian) of southern utah, usa rachel e. nottrodt and andrew a. farke ........30 new shallow snouted species of velociraptor sheds light on intraspecific variation in velociraptor mongoliensis and possible niche partitioning between species mark j. powers, mark a. norell, and philip j. currie ........31 reconstructing life history of the sabre-toothed cat smilodon fatalis using bone histology ashley r. reynolds ........32 identifying competitive exclusion in the vertebrate fossil record: lessons from early vertebrate morphometrics bradley scott and philip anderson ........33 canadian society of vertebrate palaeontology 2021 abstracts 7 a hesperornithiform (avialae: ornithuromorpha) from the upper cretaceous nemegt formation (lower maastrichtian) in mongolia tomonori tanaka, yoshitsugu kobayashi, yuong-nam lee, robin sissons, michael ryan, tsogtbaatar chinzorig, and khishigjav tsogtbaatar ........35 a kinetic model of the palaeognath ribcage with implications for understanding avian ventilation yan-yin wang, and corwin sullivan ........36 taxonomy of a new goniopholidid specimen from the upper jurassic morrison formation and their diversity in north america junki yoshida, atsushi hori, yoshitsugu kobayashi, michael j. ryan, yuji takakuwa, and yoshikazu hasegawa ........37 how to make monsters: cladistic analysis of ontogeny recovered evidence of anagenesis in north american tylosaurines amelia r. zietlow ........38 vertebrate anatomy morphology palaeontology 9:1–39 8 lissamphibia: a polyphyletic group within temnospondyli? thomas arbez department of earth sciences, carleton university, ottawa, on, canada; thomasarbez@cunet.carleton.ca phylogenetic relationships between lissamphibians (frogs, salamanders and caecilians) and their fossil relatives (i.e., non-amniotic extinct tetrapods) is a century old question, yet still actively debated, and in spite of phylogenetic matrices including more and more taxa and characters. several hypotheses about lissamphibia relationships are still discussed: lissamphibia as a monophyletic group included among the temnospondyli (temnospondyl hypothesis – “th”), or among lepospondyls (lepospondyl hypothesis “lh”), or as a polyphyletic group divided among the temnospondyls and lepospondyls (polyphyletic hypothesis – “ph”). the absence of consensus regarding the position of lissamphibians is attributed to the lack of specimens displaying a mosaic of characters specific to lissamphibians and to a particular clade of extinct non-amniote tetrapods. the most ancient fossils attributed to lissamphibians are indeed already extremely similar to extant lissamphibians and share few similarities with extinct non-amniote tetrapods. this difference is particularly visible with the great reduction of the number of cranial bones in the extant lissamphibians by comparison with the extinct non-amniote tetrapods. here, a cladistic phylogenetic analysis made with paup and including all the major groups of extinct non-amniote tetrapods, as well as lissamphibians and amniotes (63 taxa and 213 characters), reveals methodological aspects also have an important influence on the resolution of lissamphibian relationships. the phylogenetic analysis was divided into three variants (when compared to a reference) in order to test different character treatments (e.g., ordered vs unordered characters), as well as the impact of the inclusion or exclusion of some characters (e.g., character coding the presence or absence of a given bone). interestingly, different hypotheses of the position of lissamphibians, as well as their monophyly or polyphyly, were recovered based on different tests of the same matrix, allowing comparison of these hypotheses within a constrained framework (i.e., comparing topologies that are not the product of analyses with great differences in taxon or character sampling, as it could be when comparing different studies). the comparison of the different hypotheses recovered here, in terms of tree length, character support as well as character transformation coherence shows that the lissamphibian’s monophyly (th and lh) is mainly supported by the “absence of bones” without any exclusive synapomorphies. a hypothesis of a polyphyletic lissamphibia within temnospondyli (th-p), where frog and salamanders are found within the dissorophoidea and caecilians are found within brachyopidae, appears to be the most coherent in terms of character transformations despite not being the most parsimonious overall (by a few steps). in addition, the th-p hypothesis seems to solve several inconsistencies among the th, lh and ph (e.g., multiple bone reappearances or multiple reversions of morphologically complex character states). so, the classical view of a monophyletic lissamphibia is weakly anatomically supported as the synapomorphies would only be the “absence of bones”. the resulting similarity appears to be due to a similar cranial simplification process already known to be happen convergently in different extinct non amniotic tetrapod groups (e.g., lepospondyls) and likely due to paedomorphosis events. the fact that frogs, salamanders and caecilians do not form a monophyletic group when including extinct non-amniote tetrapods would explain why currently all the synapomorphies exclusive to the lissamphibia are based on soft tissues and not hard tissues, such as bones. canadian society of vertebrate palaeontology 2021 abstracts 9 first occurrence of a sea turtle (clade panchelonioidea, superfamily chelonioidea) from the dinosaur park formation of saskatchewan, canada emily l. bamforth1,2 and hallie p. street3 1royal saskatchewan museum, t. rex discovery centre, eastend, sk, s0n 0t0, canada; emily.bamforth@gov.sk.ca 2university of saskatchewan, department of geological sciences. saskatoon, sk, s7n 5e2, canada 3edmonton, ab, canada; hallie.street@gmail.com though relatively uncommon, sea turtles (clade panchelonioidea) are an intriguing component of western canada’s cretaceous marine faunas. studies of panchelonioid diversity patterns within the late cretaceous western interior sea suggest, for reasons not yet fully understood, that these animals favoured southern portions of the western interior sea (nicholls and russell 1990), occurring much less frequently in canada than in the united states. in saskatchewan, panchelonioids are represented by just two occurrences from the santonian niobrara formation along the manitoba escarpment, and one from the upper campanian bearpaw formation of southwest saskatchewan (nicholls et al. 1990). the niobrara formation specimens, a humerus (rskm p2077.64) and other fragmentary remains (rskm p2077.31) were described by nicholls et al. (1990) as protostegids, largely based on their small size. protostegidae is an extinct basal panchelonioid group which includes the giant sea turtle archelon. it is the sister taxon to the chelonioidea, which includes nearly all other known sea turtles (evers et al., 2019). the bearpaw formation specimens, small rib pieces and a badly weathered peripheral fragment (cmn 40660), could not be identified beyond chelonioidea (nicholls et al. 1990). herein is described the first occurrence of a chelonioid sea turtle from marine strata within the dinosaur park formation of saskatchewan. rskm p3197.198 is a left costal plate of the carapace, with a maximal length of 150 mm, maximal width of 90 mm in width, and maximal thickness of 16 mm. while broken along its medial margin, the lateral peripheral edge is reasonably well preserved. the costal plate is broad and slightly convex dorsally, with no noticeable suturing or ornamentation. the specimen was collected in 2016 from a marine bonebed near the hamlet of herschel, saskatchewan. recent studies have placed the herschel marine bonebed (hmb) within a marine interval of the upper dinosaur park formation, in a shallow-marine barrier-island basin environment (street et al. 2019). the hmb has yielded a high diversity of marine vertebrates, including ichthyodectids, enchodus sp., protosphyraena sp., ischyodus rayhaasi, hybodontids, odontaspidids and other lamniforms, as well as polycotylid and elasmosaurid plesiosaurs, and mosasaurine and plioplatecarpine mosasaurs. in a review of marine turtles from the late cretaceous of alberta, brinkman et al. (2015) identified at least three genera of chelonioids from this province: nichollsemys, lophochelys and kimurachelys. nichollsemys is known from open marine sediments of the bearpaw formation (brinkman et al. 2006), while kimurachelys and the specimens ascribed to lophochelys are from the lethbridge coal zone of the uppermost dinosaur park formation (brinkman et al. 2015). rsm p3197.198 is significantly larger than the alberta specimens referred to lophochelys, and both nichollsemys and kimurachelys are known only from cranial material. therefore, more work and more specimens will be required to determine if rskm p3197.198 can be ascribed to any of these taxa, or if it represents the first occurrence of another taxon in the northern western interior seaway. comparison of rskm p3197.198 from the hmb with the alberta material raises an intriguing question about the possible paleoenvironmental preference of canadian chelonioids. although not necessarily directly contemporaneous with the lethbridge coal zone, the hmb represents a similar shallow-marine, nearshore environment. brinkman et al. (2015) suggested that chelonioids may have been brackish-water or even freshwater tolerant. this may also apply to rskm p3197.198, which was found in a similar paleoenviroment. although the sample size is small, chelonioid diversity appears to be higher in nearshore, shallow-marine or estuarine vertebrate anatomy morphology palaeontology 9:1–39 10 deposits. more specimens and more research could help to elucidate is this was a true biological signature, and if chelonioid sea turtles preferred these habitats over the open ocean. rsm p3197.198 represents the largest and most diagnostic chelonioid specimen known from saskatchewan. the collection of additional specimens from marine sediments of the dinosaur park formation may reveal important information on the diversity and paleoecology of marine turtles in western canada. literature cited brinkman, d., m. hart, h. jamniczky, and m. colbert. 2006. nichollsemys baieri gen. et sp. nov, a primitive chelonioid turtle from the late campanian of north america. paludicola 5:111–124. brinkman, d.b., m. densmore, m. rabi, m.j. ryan and d.c. evans. 2015. marine turtles from the late cretaceous of alberta, canada. canadian journal of earth sciences 52:581–589. evers, s.w., p.m. barrett., and r.b.j. benson. 2019. anatomy of rhinochelys pulchriceps (protostegidae) and marine adaptation during the early evolution of chelonioids. peerj 7:6811. nicholls, e.l., and a.p. russell. 1990. paleobiogeography of the cretaceous western interior seaway of north america: the vertebrate evidence. palaeogeography, palaeoclimatology, palaeoecology 79:149–169. nicholls, e.l., t.t. tokaryk, and l.v. hills. 1990. cretaceous marine turtles from the western interior seaway of canada. canadian journal of earth sciences 27:1288–1298. street, h.p., e.l. bamforth, and m.m. gilbert. 2019. the formation of a marine bonebed at the upper cretaceous dinosaur park-bearpaw transition of west-central saskatchewan, canada. frontiers in earth science 7:209. potential preservation of keratinous tissues associated with frill ornamentation of an immature centrosaurus (ornithischia, ceratopsidae) caleb brown royal tyrrell museum of palaeontology, box 7500, drumheller, ab, canada, t0j 0y0; caleb.brown@gov.ab.ca the recognition and description of keratinized epidermal structures in dinosaurs is becoming increasingly common. within ornithischia these keratinous structures include bristles/filaments (psittacosauridae, heterodontosauridae, neornithischia), scaly skin (various taxa), keratinous osteoderm scales (ankylosauria), rhamphothecae (i.e., keratinized beaks) (hadrosauridae), and hooves (hadrosauridae/ankylosauria). the skulls of the ceratopsidae possess several bony (i.e., osseous) features which were likely capped by robust keratinized tissues including rhamphothecae on the rostral (i.e., rhinotheca) and predentary (i.e., gnathotheca), and keratinous sheaths for the nasal and postorbital horns, and likely the frill and jugal horns (i.e., epiossifications) as well. despite this high potential for keratinous preservation in ceratopsid skulls, and the abundant fossil record of this group, direct evidence of its preservation is rare to non-existent. in 2019, a small parietal of centrosaurus (tmp 2019.012.0122) was collected from low in the dinosaur park formation (campanian) of alberta. during preparation, the preparator discovered several flat, semi-circular to crescentic structures located under (i.e., stratigraphically beneath) the parietal within the jacket. importantly, a broken and displaced section of lateral ramus of the parietal was found at the same level as these structures. due to their shape and association they were initially thought to be unfused frill epiossifications (i.e., epiparietals), however breaks reveal their composition to be entirely ironstone with no bone component. a return to the quarry later in the season located more structures in the spoil pile of the jacket (i.e., matrix removed to lighten the jacket). canadian society of vertebrate palaeontology 2021 abstracts 11 in total eight structures are preserved. the specimens vary from semi-circular to crescentic in shape, with the curved/convex margins having a rounded beveled edge, while the flat/concave ‘basal’ margin often shows a concave facet-like edge. the basal margin of one specimen also shows a bi-lobed facet reminiscent of the epiossification spanning the parietal squamosal contact. the specimens vary in size, with basal widths of 30-80 mm, basalapical heights of 21–41 mm, and thickness of 6–11 mm, with these three measurements scaling approximately isometrically. the surface texture of the structures is distinctive, bearing parallel ridges and grooves, approximately 1 mm in width. in particular, on the rounded margins these striae form a distinctive braided or ropey appearance with parallel lineation showing a larger-scale sigmoidal pattern along the periphery of the elements. more centrally, one of the flat surfaces of each element shows a radial pattern of striae, while the opposite side has a subtler and more random pattern. the parietal preserves the midline bar, right lateral ramus and much of the posterior ramus, missing the left side. p1 loci (the medial-most parietal horn positions) are preserved on both left and right sides of the parietal, with a gap in the right p2 (and p3?) area, followed by four right lateral loci (p3–p6 or p4–p7 — lateral parietal horn positions) to the squamosal suture, with all loci expressed as thin, subtle scallops. the parietal is 391 mm long (sagittal length) and 317 mm wide (right half width), one of the smallest known for centrosaurus. the thickness and convex rounded bevel of the posterior and lateral edge of the parietal correlate well with both the thickness and concave facets on the flat edge of the structures. the size, shape, ornamentation development, and mottled texture of the parietal are consistent with an early subadult stage, comparable to, but smaller and potential earlier than, tmp 1995.175.0064 (470 mm x 335 mm) and cmn 11839 (496 mm x 366 mm). centrosaurine parietals of similar, or younger, ontogenetic stage are not known to have preserved epiossifications, whereas larger/older specimens show associated and then fused epiossifications. these structures are tentatively identified as fossils preserving the shape, but not organics, of keratinous sheaths associated with parietal horn loci. if this interpretation is correct, this specimen indicates that that keratinous horns may ontogenetically precede the development of the epiossification at parietal loci. further, the size of these keratinous horns is larger and more exaggerated than would be expected for a specimen at this ontogenetic stage. alternate interpretations or identifications of these structures are welcome. development and evolution of regionalization within the avian axial column hoai-nam n. bui and hans c.e. larsson redpath museum, mcgill university, montreal, qc, h3a 2k6, canada; hoai-nam.bui@mail.mcgill.ca; hans.ce.larsson@mcgill.ca the origin of birds from their terrestrial antecedents was accompanied by a wholesale transformation of their skeleton as they transitioned from a terrestrial to an aerial realm. a significant aspect of this dramatic transformation is the reduction of separate vertebral elements into regional fusions to increase axial rigidity. specifically, the transition from non-avialian theropods to highly derived birds is accompanied with the loss of an elongate tail, fusion of posterior caudals into a pygostyle, a broadly fused synsacrum and, sometimes, a notarium. this is partially mirrored within the development of the axial column, with the axial column experiencing increasing regionalization and the loss of individual skeletal elements through vertebral fusions. using a detailed description of the morphological development of the axial column in the model domestic chicken, gallus gallus, we present a map of axial chondrification and ossification based on discrete characters. we find that delays in ossification occur in conjunction with the formation of fusions. our study shows that the pattern and sequence of fusion and ossification during development may reflect the presence of independent modules, or functional units, as subsets vertebrate anatomy morphology palaeontology 9:1–39 12 within the typical regions of the avian axial column. interestingly, few of these fusion modules correspond to the initial axial hox expression patterns, suggesting another patterning mechanism is driving axial fusion regionalization. additionally, two regions of fusion are discovered in the synsacrum. the anterior region of seven fused synsacrals may correspond to the non-ornithuran pygostylian synsacrum of the same number of vertebrae. this work provides further insight into the evolution of modern birds utilizing an integration of anatomical, developmental and evolutionary perspectives that can be used for future applications in paleontology. first definitive occurrence of polycotylidae (shortnecked plesiosaurians) from non-marine sediments of the dinosaur park formation of alberta: evidence for a multi-taxic, freshwater plesiosaurian assemblage james a. campbell1 and caleb m. brown2 1department of biological sciences, university of calgary, 2500 university drive nw, calgary, ab, t2n 1n4, canada; james.campbell2@ucalgary.ca 2royal tyrrell museum of palaeontology, box 7500, drumheller, ab, t0j 0y0, canada; caleb.brown@gov.ab.ca non-marine to paralic sediments of the dinosaur park formation (dpf) have produced a stratigraphically extensive record of plesiosaurian remains (n = 105 individuals). the majority of this material comes from dinosaur provincial park (dpp), where the dpf is approximately 70 m thick. about 42% of this material is diagnostic to the family level, of which the majority (95%) is referable to elasmosauridae (i.e., long-necked plesiosaurians). about 19% of the elasmosaurid material is referable to the recently named fluvionectes sloanae, whose remains extend from 25 to 56 m above the base of the dpf. in addition to these elasmosaurid occurrences, three isolated teeth (tmp 1987.048.0042, 2001.012.0151, and 2002.012.0051) from the dpf of dpp were tentatively identified as polycotylid (i.e., short-necked plesiosaurians) in 2005. these teeth represent the only published evidence that polycotylids inhabited non-marine to paralic environments of the dpf. juvenile polycotylid remains are also known from marginal marine sediments of the dpf near herschel, saskatchewan. we re-examined these teeth and found that they are labiolingually compressed and have smooth (i.e., lacking enamel ridges) labial surfaces, as in elasmosaurids but not polycotylids, and are morphologically similar to those of fluvionectes; we therefore identify them as elasmosaurid. although this would bring the occurrence of polycotylids from the dpf of alberta into doubt, we also report on two previously undescribed isolated polycotylid centra (tmp 1980.016.0422 and 2020.012.0008) from the dpf in dpp. both specimens are identified as cervical centra, based on the presence of rib facets, and a ventral keel separating two foramina subcentralia. the neural arch appears to be unfused in both specimens, suggesting that these individuals had not reached full osteological maturity, as is the case for most plesiosaurian remains from the dpf. these centra are nearly circular in articular view and are anteroposteriorly short, both of which are characteristic of polycotylids. these centra would have been slightly longer in life, as the articular rims have been lost to abrasion. taking this into account, these centra are proportionately shorter than most other polycotylid taxa, so this may represent a diagnostic feature. both specimens were collected from an interval between 30 and 40 m above the base of the dpf, overlapping with fluvionectes, from palaeochannel sediments that are thought to have been deposited at least 100 km inland from the western interior seaway. it is likely that these centra were transported a considerable distance downriver, given their isolated and moderately abraded conditions. canadian society of vertebrate palaeontology 2021 abstracts 13 we believe that the low ratio of polycotylids relative to elasmosaurids (1:21) in non-marine to paralic sediments of the dpf likely represents an ecological signal and not a sampling or taphonomic bias, given the long history of plesiosaurians collected from this unit, and the two clades having similar taphonomic profiles. elasmosaurid remains are also more abundant than polycotylid remains in marginal marine sediments of the dpf near herschel, saskatchewan, and in the marine bearpaw formation. plesiosaurian remains are particularly common in the interval of the dpf that produced these two centra, which may in part explain why polycotylids have not yet been found elsewhere in this unit. the dpf represents one of only five multi-taxic, non-marine plesiosaurian assemblages known, the others being the late jurassic spilsby sandstone formation of england, the berriasian deister formation of germany, and the late campanian/early maastrichtian la colonia and allen formations of argentina. the differing diet and feeding strategies between polycotylids and elasmosaurids, as reflected in their tooth and cranial morphologies, may have enabled these two families to co-exist within the non-marine to paralic dpf, as they did in the marine realm. palaeopoems: a digital anthology highlighting a unique form of science communication brigid e. christison1, michael g.w. thompson2, and katrin emery3 1biology department, carleton university, 1125 colonel by drive, ottawa on, k1s 5b6, canada; brigidchristison. cmail.carleton.ca 2museum of natural sciences, university of saskatchewan, 114 science place, saskatoon sk, s7n 5e2, canada; michael.g.w.thompson@gmail.com 3ottawa, on, k1y 2v4, canada; katremery@gmail.com poetry is a form of science communication (scicomm) that is able to express the thoughts and feelings of those who study fossils in a unique way. poetry can communicate scientific concepts in a language that is accessible to a wider audience than academic writing alone. palaeopoems.com is a digital anthology founded in 2018 that aims to compile as many of these poems as possible. academics have written poetry to discuss complex scientific ideas, feuds, and even morphological descriptions since at least the 1800s and continue to do so. these poems are therefore both educational and historically significant, letting readers understand prevailing ideas about palaeontology from the times they were written. palaeopoems.com aims to make these poems as available as possible to both researchers and the public by presenting them alongside their primary sources. each month, palaeopoems.com features a poem related to the field of palaeontology, accompanied by analyses of the historical and scientific aspects of their written content. these breakdowns allow readers to understand the terminology used within and provide context for certain verses. featured poems are also accompanied by contemporary artwork from different artists. by including contemporary artwork with each poem, our goal is to show that historical poetry is not merely an outdated curiosity, but still retains value as a genuine form of modern scicomm. contemporary artwork highlights the scientific message of the poems themselves in ways that are also promotional for each featured poem, allowing the blog to reach a wider audience. another major goal of the palaeopoems project is to encourage poetry writing among academics and palaeontology enthusiasts. palaeopoems.com issues weekly poetry-writing prompts on social media, usually about a relatively broad palaeontological topic. for scientists not used to writing in verse, these poem prompts are an opportunity to think about topics in a less conventional way. our goal with this challenge is to promote the practice of writing palaeopoems so that academics, science communicators, and other people can become more familiar with these ways of writing and thinking and in turn inform them about the value of poetry and other writing styles as scicomm. vertebrate anatomy morphology palaeontology 9:1–39 14 evolution of marine ecosystems, a global view from the early cretaceous marine tetrapods of colombia dirley cortés1,2,3, hans c.e. larsson1, erin e. maxwell4, alexandre demers-potvin1, hoai-nam bui1, anthony smith1, and mary luz parra-ruge3 1redpath museum, biology department, mcgill university, 859 sherbrooke st. w., montréal qc h3a 0c4, canada; dirley.cortes@mail.mcgill.ca; hans.ce.larsson@mcgill.ca; alexandre.demers-potvin@mail.mcgill.ca; hoai-nam.bui@mail. mcgill.ca; anthony.smith2@mail.mcgill.ca 2smithsonian tropical research institute, balboa-ancón 0843–03092, panamá, panamá 3centro de investigaciones paleontológicas, kilómetro 5.2 vía santa sofía, villa de leyva, colombia; mlparra@centropaleo.com 4staatliches museum für naturkunde, rosenstein 1, 70191 stuttgart, germany; erin.maxwell@smns-bw.de this research investigates how the ancient marine ecosystems spanning the establishment of the hispanic corridor (a seaway linking the eastern pacific and western tethyan oceans) evolved, and assembles a comprehensive dataset from multiple diverse fossil localities that temporally and spatially span a time of large-scale global sea level rise, temperature rise, and tectonic rifting that connected the atlantic and pacific oceans during the early cretaceous, over 130 million years ago. these data will be used to estimate the aspects of these ecosystems that were most stable and which evolved during this dramatic environmental event. emphasis is placed on high ecological trophic levels, because as we know from the modern world, predators offer the most robust signals of ecosystem complexity and food web interactions. to address how marine reptiles responded to biogeographic changes (opening of the hispanic corridor), climate (temperature), and sea-level changes, the marine fauna from the paja formation (hauterivian-barremian) of colombia is being used as a model system to investigate evolutionary patterns of top predators (i.e., origination, extinction, anatomical rates) using accurate time-calibrated phylogenies. we propose a hypothesis that biotic factors will show significant signatures to support a hotspot of high origination rates, low extinction rates, high morphological rates of evolution, and high endemism. preliminary results show remarkable insights. first, the occurrence of a colombian barremian teleosauroid demonstrates that the thalattosuchian teleosauroid lineage, thought to be extinct, survived the jurassic / cretaceous extinction. with a body length of 9.6 m, this specimen is one of the largest known teleosauroids and the youngest known for the lineage. this finding supports the hypothesis that tropical water temperature played an important role in controlling the diversity and distribution of these large marine predators. second, the descriptions of ichthyosaur material reveal the first hypercarnivore ichthyosaur from the cretaceous, which opens up questions about food web structures for jurassic-cretaceous ecosystems. finally, a 3d surface scan of a pliosaur from the paja formation reveals numerous cranial autapomorphies, which provide distinguishable information to place this new genus in a taxonomic and systematic context and to evaluate its phylogenetic and paleobiogeographic relevance. while most pliosaurs were certainly extinct by this time, the clade including kronosaurus and brachauchenius survived well into the late cretaceous, thus the evaluation of this sauropterygian material from the same rocks suggests the paja formation of colombia may be where some of the last pliosaurs and first elasmosaurs ever known occur. this project will set the stage for continued explorations of large-scale patterns in species diversity for other taxonomic levels for a better understanding of the consequences of the jurassic-cretaceous extinction on marine vertebrate faunas, and ultimately of the advent of today´s marine ecosystems. canadian society of vertebrate palaeontology 2021 abstracts 15 morphological analysis of a nectridean lepospondyl, diceratosaurus, from linton and five points, ohio jamey h.m. creighton1 and jason s. anderson2 1department of biological sciences, university of calgary, 2500 university dr. nw, calgary, ab, t2n 1n4, canada; jhcreigh@ucalgary.ca 2department of comparative biology & experimental medicine, university of calgary, 3330 hospital dr. nw, calgary, ab, t2n 4n1, canada; janders@ucalgary.ca lepospondyli is a group of small-bodied tetrapods traditionally including five paleozoic groups: microsauria, lysorophia, nectridea, aistopoda, and adelosondyli, united by the presence of elongate trunks and holospondylous vertebrae. however, more recent studies have shown these taxa show few consistent similarities and are likely a polyphyletic assemblage. for example, recent analyses have placed aïstopods deep on the tetrapod stem (with animals showing a progression from ‘fish’ to terrestrial tetrapod features) and lysorophia and microsauria (in part) with amniotes. nectridea, which is thought to be quite basal in the early tetrapod phylogeny, has not yet been included in some of these studies. more information needs to be collected to test the interrelationships of nectrideans among early tetrapod groups. this study focuses on diceratosaurus, a nectridean solely known from linton and five points, ohio. latex peels of the skull roof and the palate are being analyzed and illustrated by using photography and light microscopy. preliminary results suggest that diceratosaurus comprises two distinct morphs that altogether range from 14–25 cm in skull length: a broad, round-snouted morph, and a small, narrow-snouted morph which has never been seen in nectrideans before. we test several hypotheses to explain this variation including ontogenetic change, polymorphism, and the presence of multiple species. examining the smallest specimens, which are the narrow-snouted morphs, to the largest specimens which are the broad-snouted morphs, there seems to be no signs of an ontogenetic difference; the dermal ornamentation is organized with distinct pits and ridges, all bones in the skull roof are ossified, and the sutures are tightly closed in the smaller narrow-snouted morphs. this is not what one would expect if this were a juvenile form of diceratosaurus. although more work remains to be done documenting the anatomy of the palate, there are differences in the bones of the pre-orbital region of the skull and in the ornamentation around the tabular horn region. we believe multiple species to be the most likely explanation. the discovery of a second morph and these results could further support the conclusion that not only nectrideans, but lepospondyls as a group, are more diverse than originally thought. vertebrate anatomy morphology palaeontology 9:1–39 16 a morphometric analysis of the turtle manus and its implications for the palaeoecology of extinct turtles thomas w. dudgeon1,2, marissa c.h. livius3, and jordan c. mallon3,4 1department of ecology and evolutionary biology, university of toronto, 27 king’s college circle, toronto, on m5s 1a1, canada; thomas.dudgeon@mail.utoronto.ca 2department of natural history, royal ontario museum, 100 queen’s park, toronto, on, m5s 1c6, canada 3department of earth sciences, carleton university, 1125 colonel by drive, herzberg laboratories, ottawa, on, k1s 5b6, canada; marissalivius@cmail.carleton.ca 4beaty centre for species discovery and paleobiology section, canadian museum of nature, p.o. box 3443, station d, ottawa, on k1p 6p4, canada; jmallon@nature.ca among the most widely used predictors of palaeohabitat in fossil turtles is the skeletal proportions of the forelimb (humerus:ulna:manus), yet its application has been criticized on the grounds that the ternary diagrams used to represent those proportions neither control for phylogenetic effects, nor provide statistical likelihood estimates for palaeohabitat assignment. in this study, we apply linear statistical modeling to investigate the relationship between forelimb proportions and habitat among turtles, and use them to infer the palaeohabitats of problematic fossil species. we performed three morphometric analyses: the first focusing on the major components of the forelimb (humerus, ulna, and manus), the second on the manus proper (metacarpals, phalanges, and unguals), and the third combining these two datasets (humerus, ulna, metacarpals, phalanges, unguals). for each of these datasets, we used phylogenetic generalized least squares regression to extract the residuals for subsequent analysis, which are corrected for both size and the phylogenetic non-independence of taxa. each set of residuals was subjected to a linear discriminant analysis (lda) to determine the predictive accuracy of these measurements on habitat, which was divided into the following six bins: ‘all bodies of water’, ‘moving or large bodies of water’, ‘primarily on land’, ‘primarily on land often in water’, ‘primarily on land seldom in water’, and ‘stagnant or small bodies of water’. we then used the discriminant functions to predict the palaeohabitats of the extinct basilemys variolosa, palaeochersis talampayensis, proganochelys quenstedti, eunotosaurus africanus, and odontochelys semitestacea. the manual dataset and combined forelimb and manual dataset performed similarly well, with classification accuracies of approximately 82% and 83%, respectively. the forelimb dataset performed poorest, with a classification accuracy of just 72%. based on these analyses, basilemys variolosa is resolved as a fully terrestrial turtle that preferred dry environments with welldrained substrates; palaeochersis talampayensis and proganochelys quenstedti are similarly recovered as highly terrestrial; eunotosaurus africanus was likely primarily terrestrial, occasionally venturing to the water; and odontochelys semitestacea was likely semi-aquatic, spending significant periods of time both on land and in the water. taken together, these results suggest that manual proportions provide a particularly powerful habitat proxy in turtles, and provides still further evidence that stem turtles were primarily terrestrial in nature. canadian society of vertebrate palaeontology 2021 abstracts 17 a new plastomenine trionychid (testudines: pantrionychidae) from the milk river formation of southern alberta (cretaceous: santonian) shauna c. edgar1, don b. brinkman2, michael j. ryan3, and david c. evans1,4 1department of ecology and evolutionary biology, university of toronto, 25 willcocks street, toronto, on, m5s 3b2, canada; shauna.edgar@mail.utoronto.ca 2royal tyrrell museum of palaeontology, p.o. box 7500, drumheller, ab t0j 0y0, canada; don.brinkman@gov.ab.ca 3department of earth sciences, carleton university, 1125 colonel by drive, ottawa, on, k1s 5b6, canada; michaelj.ryan@carleton.ca 4department of natural history, royal ontario museum, 100 queen’s park, toronto, on, m5s 1c6, canada; d.evans@utoronto.ca the pre-campanian trionychid fossil record in north america comprises highly fragmentary specimens, which are often not identifiable beyond pan-trionychidae. here, we describe a new species of plastomenine soft shell turtle based on a partial carapace and plastron (rom 56647) from the santonian milk river formation of southern alberta, dated at approximately 84 ma. plastomeninae is characterized by the complete suturing of the plastral bones along the midline, a crescent-shaped entoplastron, and enlarged eighth costals. rom 56647 has a unique combination of plastomenine characters (i.e., midline contact of posterior plastral elements, dorsoventrally long eighth costal) and apomorphies (emarginate nuchal, enlarged tubercles on the carapace, wide pygal notch with a straight anterior edge, and fused hyo-hypoplastron) that allows us to identify it as a new taxon. phylogenetic analysis using parsimony places the new taxon within plastomeninae as the sister taxon to a clade containing plastomenus, helopanoplia and hutchemys. this phylogenetic position implies that aspideretoides foveatus, atoposemys, and gilmoremys, all of which have a more basal position within plastomeninae, and had ghost lineages extending at least to the santonian. as the oldest pan-trionychid that can be described to the species level in north america, the new taxon represented by rom 56647 offers novel insights into both the early evolution of trionychids in north america and the pre-campanian biodiversity of turtles in what is now southern alberta. life history of an archaic placental mammal, pantolambda bathmodon (placentalia, pantodonta) gregory f. funston1, paige e. depolo1, sarah l. shelley1, john r. wible2, thomas e. williamson3, and stephen l. brusatte1 1school of geosciences, university of edinburgh, edinburgh, uk; gregory.funston@ed.ac.uk 2carnegie museum of natural history, pittsburgh, pennsylvania, usa 3new mexico museum of natural history and science, albuquerque, new mexico, usa the rise of mammals after the extinction of the dinosaurs remains one of the most enigmatic intervals in the evolution of mammals. a relatively sparse paleocene fossil record and confusing interrelationships between taxa means that little is known of the evolution, ecology, and biology of these animals. as a result, the life history of these organisms is completely unstudied, despite likely playing a key role in the ability of these clades to rapidly proliferate and increase in body size in recovering ecosystems. however, intensive collection efforts in vertebrate anatomy morphology palaeontology 9:1–39 18 the san juan basin of new mexico in the last decade have drastically improved the record of many paleocene mammals, and offer the first opportunity to address questions about the life history of these animals. here, we present preliminary results of an in-depth paleohistological analysis of pantolambda bathmodon, an early, possibly gregarious pantodont, using an ontogenetic series of individuals. pantodonts were bizarre, herbivorous eutherians of unknown phylogenetic affinity, and were among the first mammal lineages to reach large body sizes in the paleocene. in examining both dental and skeletal records of growth from the same individuals, including a juvenile still bearing deciduous teeth, our study is among the most comprehensive paleohistological analyses of any fossil mammal. this intensive approach allows for unprecedented insights into the life history of this species. neonatal lines in the teeth indicate that the deciduous premolars and the first upper molar were erupted prior to birth, similar to precocious, nidifugous mammals today. daily incremental lines in the enamel and dentine suggest rapid crown formation times (~45–70 days) and a gestation period of at least 15 weeks. a stress line in the postcranial bones, recording an anomalous decrease in growth towards the end of this individual’s life, may represent the weaning event. in the absence of geochemical evidence, it is unclear which of two stress lines in the teeth corresponds to this event, but these lines occur roughly one and two months after birth, respectively. the weanling perished approximately 2.5 months after birth, weighing about 17 kg. an adult individual exhibiting severe wear on the dentition allows us to estimate maximum longevity in pantolambda bathmodon at about 7 years. in comparison with life history data on living mammals from the pantheria dataset, pantolambda bathmodon had a gestation length and weaning duration below average for a placental of its adult body size (42 kg), but within the range of known variation. however, its lifespan was exceptionally short, falling outside the bounds of comparable living mammals. together, these lines of evidence suggest a relatively rapid pace of life in pantolambda bathmodon, despite its relatively large body size. ongoing sampling of more individuals and geochemical analyses should allow for estimation of time to sexual maturity and help to confirm the identity of the weaning line, completing our picture of the life history of this pioneering species. revisiting the sedimentology and depositional evolution of the cypress hills formation (eocene – miocene) in southwestern saskatchewan, canada: implications for vertebrate microfossil assemblages meagan m. gilbert saskatchewan geological survey, box 104, la ronge, saskatchewan, s0j 1l0 meagan.gilbert@gov.sk.ca the eocene to miocene cypress hills formation (chf) spans 28 million years, and forms the conglomeratic caprock of the cypress hills plateau in southwestern saskatchewan. the formation records one of the last major sedimentation events in the western plains of north america at a time when the world was undergoing major climate fluctuations. as well, the chf contains the only high latitude, non-polar mammalian fossil assemblage known (uintan to whitneyan land mammal stages) in north america. several palaeontologic studies have largely focused on taxa recovered from vertebrate micro and macrofossil sites, which have shed light on diversity and faunal turnover during this critical time. in contrast, the chf has been the focus of few detailed geologic studies, reflected in the relatively poor constraint on the regional stratigraphy and timing of depositional events. recently a field program has been underway to establish a depositional model for the chf immediately north of eastend, saskatchewan augmented by fauna recovered from vertebrate microfossil sites. preliminary results have illustrated a canadian society of vertebrate palaeontology 2021 abstracts 19 complex network of multi-episode cut-and-fill braided channel deposits and their associated channel bars and floodplains. this complexity has serious implications for understanding the stratigraphic relationships between fossil sites and the strata they are recovered in, particularly regarding vertebrate microfossil assemblages. this ongoing study highlights the importance of high-level sedimentology and stratigraphy for understanding fossil assemblages in time and space, and will provide invaluable context for future paleontologic work undertaken in the region. dinosaur fossil discovery using remotely piloted aircraft systems and spectral mixture analysis sean herridge-berry1, caleb m. brown2, derek r. peddle1, brian j. pickles3, and craig a. coburn1 1department of geography & environment, and alberta terrestrial imaging centre (atic), university of lethbridge, lethbridge, ab, t1k 3m4, canada; s.herridgeberry@uleth.ca; derek.peddle@uleth.ca; craig.coburn@uleth.ca 2royal tyrrell museum of palaeontology, p.o. box 7500, drumheller, ab, t0j 0y0, canada; caleb.brown@gov.ab.ca 3school of biological sciences, university of reading, whiteknights, reading, rg6 6ex, uk; b.j.pickles@reading.ac.uk prospecting for new fossil sites remains an integral part of palaeontological research. given that fossil discoveries generally rely on exposed bedrock, the most productive areas are often associated with similar geophysical features, including low vegetation cover, high topographic relief, and high rates of erosion, such as badlands, deserts, and/or arctic outcrop. these regions also tend to have limited transportation infrastructure, are remote and rugged, and can be geographically extensive in area, posing limitations to terrestrial access. given these limitations, potential fossil-bearing areas may represent prime areas for remote sensing where imagery can be collected in a relatively short amount of time from platforms such as satellites, airplanes, helicopters, or remotely piloted aircraft systems (rpas, a.k.a. drones). the sensors aboard these platforms measure the amount of solar radiation in different wavelengths as reflected by the ground surface to provide information about the unique reflectance patterns of the target. these technologies have revolutionized the acquisition of large-area georeferenced imagery useful for ecological interpretation and resource exploration. they may have utility in detecting exposed fossil resources that are indicative of a larger area (10–100 m), high-density (10–100 bones/m2) accumulations of large bones, representing monodominant or multi-taxic bonebeds. to date, the use of these aerial platforms in palaeontology has been minimal, and when used, has been restricted to mapping known fossil occurrences – primarily trackways such as in petti et al. (2018). however, it remains to be tested if, and to what extent, remote sensing can perform in the original detection of these extensive fossil resources. this research represents a laboratory and field-based proof-of-concept test for the remote sensing of fossil resources, specifically vertebrate bonebeds, using the campanian-aged dinosaur park formation (dpf), dinosaur provincial park, alberta, as a case study. the markers used in this study include weathered fossil bones and modern lichen colonies (xanthoria sp.), which may preferentially colonize fossil bone relative to other substrates. fossil bones can possess diverse microbial communities (saitta et al. 2019), and a study of antarctic eocene fossils revealed colonisation by several lichen species (garcía et al. 2020). distinct geological features such as palaeo-channels and point bar deposits may also represent markers to be detected. due to the small size of most fossil targets, spectral mixture analysis (sma), an advanced image processing technique, is being investigated as a sub-pixel scale analytical approach following some of the key sma protocols developed by peddle and smith (2005). to test this, high-resolution spectral measurements of these characteristic fossil targets were collected in a controlled laboratory setting at the alberta terrestrial imaging centre (atic). fossils, lichen-covered fossils, and geologic samples were loaned from the royal tyrrell vertebrate anatomy morphology palaeontology 9:1–39 20 museum of palaeontology (rtmp) and provided representative examples of targets found from dpp for spectral measurement at atic. spectral measurements were acquired in the atic remote sensing lab at the university of lethbridge using an analytical spectral devices (asd) fieldspec-3 full-range spectroradiometer (350–2500 nm). spectra to derive reflectance were acquired with reference to a calibrated white spectralon panel (pressed polytetrafluoroethylene — ptfe). the spectra were post-processed and adjusted to account for multi-detector noise at sensor boundaries of 1000 nm and 1900 nm. amongst the samples, there were four distinct patterns of reflectance: fossil bone, sediment, modern lichen, and teeth. this shows that these representative targets are sufficiently different spectrally and suitable for input to sma for spectral separation with pixel-scale targets. these data provide a basis for laboratory spectral analysis and as a planned input for sma of imagery from rpas missions (described below). for example, we expect that the unique reflectance signatures of fossil bone and teeth, sediment, and lichen are suitable endmember spectra for input to sma. in september 2020, field deployment of a rpas took place at dpp with atic, rtmp and alberta parks staff, and following covid-19 protocols. five sites were imaged at two altitudes (30 m and 100 m above ground level, or agl) using two camera systems. multispectral images were acquired using a micasense rededge-m five-band camera, with simultaneous rgb images acquired using a dji x4s gimble-mounted camera. the multispectral camera captured images in five bands allowing data to be collected from the blue, green, red, near-infrared, and red-edge areas of the electromagnetic spectrum while the rgb camera acquired images in the blue, green, and red portions of the spectrum. after images were mosaicked using stitching procedures in pix4d software, the resulting images had nominal ground sample distances as small as 0.8 cm at 30 m agl. based on analysis of these remote sensing lab and rpas products to date, the high spatial resolution imagery combined with the spectroradiometer data provides appropriate inputs to sma. using these data and algorithms together offers new opportunities for detecting fossil resources in the dpf and may have utility in other similar but more remote, extensive, and challenging fossil-bearing outcrops. literature cited garcía, r., g. márquez, and c. acosta hospitaleche. 2020. richness of lichens growing on eocene fossil penguin remains from antarctica. polar biology 43:2011-2019. doi 10.1007/s00300-020-02761-9 peddle, d.r., and a.m. smith. 2005. spectral mixture analysis of agricultural crops: endmember validation and biophysical estimation in potato plots. international journal of remote sensing 26:4959-4979. doi 10.1080/01431160500213979 petti, f.m., m. petruzzelli, j. conti, l. spalluto, a. wagensommer, m. lamendola, r. francioso, g. montrone, l. sabato, and m. tropeano. 2018. the use of aerial and close-range photogrammetry in the study of dinosaur tracksites: lower cretaceous (upper aptian/lower albian) molfetta ichnosite (apulia, southern italy). palaeontologia electronica 21:118. doi 10.26879/845 saitta, e.t., r. liang, m.c.y. lau, c.m. brown, n.r. longrich, t.g. kaye, b.j. novak, s.l. salzberg, m.a. norell, g.d. abbott, m.r. dickinson, j. vinther, i.d. bull, r.a. brooker, p. martin, p. donohoe, t.d.j. knowles, k.e.h. penkman, and t. onstott. 2019. cretaceous dinosaur bone contains recent organic material and provides an environment conducive to microbial communities. elife 8:e46205. doi 10.7554/elife.46205 canadian society of vertebrate palaeontology 2021 abstracts 21 feeding ecology of the bearpaw formation mosasaur community femke m. holwerda royal tyrrell museum of palaeontology, drumheller, alberta, t0j 0y0, canada; f.m.holwerda@gmail.com the campanian sediments of the bearpaw formation yield a rich marine fauna from the northern exposures of the western interior seaway. many well-preserved mosasaur skeletons, representing most of the mosasaur taxa from this geological unit in alberta, including skulls and dentition, are housed at the royal tyrrell museum of palaeontology. good preservation of tooth-bearing bones not only allows for the study of tooth morphology, but also for analysis of dental microwear, or microscopic wear on dental surfaces, generated by tooth-tooth or tooth-food occlusion/abrasion, and geochemical analyses. microwear is categorized as small scratches, large scratches (gouges) and pits. the three most common mosasaurs from the collections were sampled for two-dimensional microwear: mosasaurus missourensis, prognathodon sp., and plioplatecarpus primaevus. the most common and large mosasauroids, mosasaurus and prognathodon, show differences in microwear between their upper and lower jaws. mosasaurus missourensis shows a high total and average number of small scratches in the premaxillary and maxillary teeth, and a low number in the dentary. prognathodon sp. shows a large amount of pits in both upper and lower tooth rows, and a high number of gouges in the maxilla. as scratches indicate feeding on softer prey, and gouges show feeding on harder prey items, this could already reveal a difference in feeding ecology between these two large mosasaurs. teeth of the less common and smaller plioplatecarpus primaevus also show a high average number of gouges and pits, in contrast to its small piscivorous tooth morphology. this could indicate regular feeding on ammonites and belemnites for this taxon. using energy-dispersive x-ray spectroscopy (edx) analysis as another independent line of evidence of mosasaur feeding in the alberta bearpaw fm., the elements strontium, calcium and barium are measured on isolated teeth. mosasaurus missouriensis plots on the resulting pca scatterplot together with elasmosaurid plesiosaurs, hybodont and cretodus sharks, indicating mainly piscivory and sarcophagy. prognathodon sp. mainly plots together with sawfish, indicating durophagy. finally, plioplatecarpus plots away from both of the larger mosasaurs, and overlaps with hybodont sharks, possibly indicating piscivory. this study hints at an efficient level of niche partitioning amongst the mosasaurs of the northern western interior seaway. a follow-up study using isotopes and three-dimensional microwear analysis will seek to confirm these findings. vertebrate anatomy morphology palaeontology 9:1–39 22 osteohistology of a thescelosaurid (dinosauria, ornithischia) fibula from the wapiti formation (campanian) of northern alberta: implications for diversity of growth strategies and osteohistological features within thescelosauridae michael naylor hudgins1, phil r. bell2, nicolás e. campione2, federico fanti3, robin l. sissons1, matthew j. vavrek4, derek w. larson⁵, and cor win sullivan1,6 1department of biological sciences, university of alberta, edmonton, ab, t6g 2e9, canada; hudgins@ualberta.ca; robin.sissons@gmail.com; corwin1@ualberta.ca 2school of environmental and rural science, university of new england, armidale, nsw, 2351, australia; pbell23@ une.edu.au; campion@une.edu.au 3dipartimento di scienze della terra e geologico-ambientali, alma mater studiorum, università di bologna, 40216 bologna, italy; federico.fanti@unibo.it 4cutbank palaeontological consulting, grande prairie, ab, t8w 0h6, canada; matthew@matthewvavrek.com 5royal british columbia museum, victoria, bc, v8w 9w2, canada; dlarson@royalbcmuseum.bc.ca 6philip j. currie dinosaur museum, wembley, ab, t0h 3s0, canada bone histological studies have provided detailed information about the diversity of, and variation in, growth strategies, life history, and behaviour in non-avian dinosaurs. however, only a few osteohistological (i.e., analyses focusing on the microscopic structure and function of bones) analyses of thescelosauridae have been conducted. here we present new histological data from a partial fibula (ualvp 50999) of a thescelosaurid from the late campanian (~73.5 ma) wapiti formation of northern alberta. the partial fibula consists of well-vascularized fibrolamellar and parallel-fibred bone with longitudinal and lamellar vasculature, as well as primary and secondary osteons, throughout. extensive secondary remodeling occurred on the posteromedial margin of the section, likely due to biomechanical stresses from locomotion as the animal grew. seven lines of arrested growth (lags) were deposited, suggesting that the individual was at least seven years old at the time of death. the individual likely reached sexual maturity based on prior growth models of reptilians and dinosaurs, although this is difficult to determine with certainty. the onset of sexual maturity in ualvp 50999 coincides with bone texture changes from the inner to outer cortex, and growth deceleration reflected in narrowing inter-lag spaces towards the periosteum. however, the individual had not reached skeletal maturity at the time of death, based on extensive secondary remodeling and the absence of an external fundamental system. this inference is consistent with prior research indicating that dinosaurs reached sexual maturity before skeletal maturity. the histology of the partial fibula suggests that the growth rate of the wapiti thescelosaurid was similar to that of haya, jeholosaurus, and oryctodromeus, and faster than that of orodromeus, but slower than that of hypsilophodon and derived ornithischians. in ualvp 50999, an interval of rapid growth appears to have taken place following deposition of the fifth lag, although growth abruptly slowed again with deposition of the last two lags. some specimens of haya and jeholosaurus show evidence of a similar growth pattern, involving ‘moderate’ growth in early life, followed by a period of rapid growth, and then slow growth later in life. however, the increases and decreases in growth rate inferred from ualvp 50999 may also indicate changing environmental conditions, niche partitioning between juveniles and adults, or random variation in the individual’s growth rate. the skeletal immaturity canadian society of vertebrate palaeontology 2021 abstracts 23 of ualvp 50999 adds to the evidence, from previous histology-based age estimates for other taxa, that most small-bodied ornithischian specimens in the fossil record represent individuals that did not live to reach skeletal maturity. whether this pattern results from an r-selected reproductive strategy in thescelosaurids, a taphonomic bias, or a random signal is unclear. a larger histological data set is necessary for future research addressing a range of fundamental questions pertaining to thescelosaurid palaeobiology, but the present analysis represents a step towards this goal and provides evidence that should prove useful in future studies of bone tissue variation and diversity of growth strategies among small-bodied ornithischians in general. impacts of miocene tectonism and climate change on diversity dynamics of carnivoran and ungulate mammals in north america blue hunter-moffatt1, and danielle fraser2 1department of earth sciences, carleton university, 1125 colonel by drive, ottawa, ontario, canada k1s 5b6; bluehuntermoffatt@cmail.carleton.ca 2palaeobiology, canadian museum of nature, po box 3443 stn “d”, ottawa on k1p 6p4; dfraser@nature.ca across modern landscapes, tectonically active, topographically complex environments (e.g., mountain ranges) support greater mammalian biodiversity than tectonically quiescent lowlands at the same latitude. one possible explanation for topographic diversity gradients is that tectonic processes promote diversification of mammals by increasing habitat heterogeneity. additionally, climate warming may increase species richness in mountainous regions as lowland taxa track their climatic niche to higher elevations. in this study, we assess the influence of landscape evolution, involving both tectonic and climatic change, on the diversity dynamics of miocene carnivoran and ungulate faunas in north america. using capture-mark-recapture (cmr) methods and fossil occurrence data from the miomap database, we calculated origination and extinction rates of carnivoran and ungulate species in five north american study regions with unique landscape histories. cmr involves repeatedly sampling, marking, and releasing organisms thus creating an “encounter history” for each individual. in palaeobiology, occurrences of fossil species divided among discrete time bins comprise the encounter histories that are used to estimate the number of species present in each time bin, sampling probabilities, and diversification rates. three regions, the columbia basin, the rocky mountains, and the southwest (i.e., california, arizona, new mexico, nevada), were tectonically active during parts of the miocene. two regions, the great plains and the gulf coast, were tectonically quiescent. we did not detect pulses of origination coincident with tectonic events in any active region, contra to our prediction. however, we found extinction peaks in the rocky mountains and southwest during the middle miocene climate optimum. this is consistent with extinction of high elevation taxa during global warming, which is predicted for numerous high latitude taxa today. we used biogeographic stochastic mapping to test for rates of dispersal among regions and found that biogeographic processes during the miocene were dominated by dispersal of species from the great plains to other study regions likely reflecting habitat tracking during climate change. together, these results suggest that interactions between climate change and topographic complexity influence mammalian dispersal and extinction dynamics, but that tectonic activity alone has not promoted speciation of large mammals at least in north america. vertebrate anatomy morphology palaeontology 9:1–39 24 new material of the oldest metamorphic salamander (amphibia, urodela) from the middle jurassic of china yields insights into palaeoecological disparity jia jia1,2,3, jason s. anderson3, and ke-qin gao1 1school of earth and space sciences, peking university, 5 yiheyuan road, beijing 100871, china; jia_jia@pku.edu.cn; kqgao@pku.edu.cn 2state key laboratory of palaeobiology and stratigraphy (nanjing institute of geology and palaeontology, cas), 39 east beijing road, nanjing, jiangsu province, 210008, china 3department of comparative biology and experimental medicine, university of calgary, 3330 hospital drive, calgary, ab, canada, t2n 4n1; janders@ucalgary.ca salamanders (total-group named caudata; crown-group named urodela) are a group of extant tailed amphibians that are ecologically diversified with individuals at adult stage living in water (aquatic), on land (terrestrial), in a tree (arboreal) or migrating between water and land (semiaquatic). how and when these ecological preferences differentiated among salamanders remains unclear because of a poor fossil record. the origin of caudata was estimated by molecular studies to have occurred during the late paleozoic, whereas the geologically oldest salamander triassurus sixtelae was documented from the middle/late triassic (~230 ma) in southwestern kyrgyzstan. the next oldest known fossil records of salamanders are found from the middle jurassic bathonian (~168–166) in several localities of eurasia (uk, russia, kyrgyzstan and china). most of these middle jurassic, and the only known triassic, salamanders are stem members of urodela as evidenced by the absence of the spinal nerve foramina in the atlas that characterize urodela. only five contemporary taxa have been found as basalmost urodeles, including kiyatriton krasnolutskii from siberia, russia; ‘kirtlington salamander b’ from kirtlington, uk and three taxa (chunerpeton, jeholotriton and liaoxitriton daohugouensis) from the daohugou fossil locality in northern china. the morphological evolutionary histories of early salamanders are insufficiently understood because most middle jurassic or earlier taxa are represented either by immature specimens (triassurus) or fragmentary/disarticulated bones (e.g., k. krasnolutskii), but the three taxa from china are represented by complete and articulated skeletons. moreover, patterns of palaeoecological disparity among early salamanders remain unclear because all stem-group and most crown-group urodeles are neotenic, except liaoxitriton daohugouensis, which represents the oldest known metamorphic salamander as evidenced by its moderate size, absence of internal and external gills, anterolaterally oriented palatal ramus of pterygoid, and extensively ossified limb structures. to date, liaoxitriton daohugouensis is known from three specimens from the middle jurassic haifanggou formation at the daohugou fossil locality, inner mongolia, china. it was originally misclassified as congeneric with the early cretaceous liaoxitriton zhongjiani from the yixian formation at the xintaimen fossil locality, liaoning province, china, but this attribution raised doubts. here we report a new, complete, and almost fully-grown specimen from the type locality. micro-ct scanning and visual examination reveal details of the dermal skull roof, suspensorium, braincase, mandible, autopodium, and tail that were previously unclear. five autapomorphies of this taxon are identified, including: parietal elongate; palatal process of pterygoid expanded; vomer expanded posteriorly, reaching close to anteroposterior ventral midpoint of cranium; cultriform process of parasphenoid shortened anteroposteriorly; and scapular blade shortened to slightly more than onehalf width of coracoid. our cladistic analyses based on a data matrix of 108 morphological characters (24% newly identified) and 22 taxa find that “l. daohugouensis” is crownward of linglongtriton and is not the sister taxon to l. zhongjiani, which enable us to transfer “l. daohugouensis” into a new genus. our results further identify “l. daohugouensis” and several mesozoic taxa including linglongtriton, liaoxitriton sensu stricto, nuominerpeton and regalerpeton from northern china as stem members of the asiatic salamander family hynobiidae, and therefore predates the origination time of hynobiidae previously estimated by molecular studies by at least 8 myr. canadian society of vertebrate palaeontology 2021 abstracts 25 the new specimen of “l. daohugouensis” has a wrinkled caudal fin and several features commonly seen in extant terrestrial hynobiids, including anteroposteriorly short skull, rounded snout, many vomerine teeth with vomerine teeth rows spanning most of the transverse dimension of the palate, and extensively ossified limb. the combination of these features suggests “l. daohugouensis” is a semi-aquatic at adult stage, a previously unknown palaeoecological preference among mesozoic salamanders. comparisons with both contemporary taxa (chunerpeton and jeholotriton) and other stem hynobiids, including the metamorphic and terrestrial nuominerpeton and the neotenic regalerpeton suggest that both life history strategies and ecological disparities have taken place by the middle jurassic bathonian stage among urodeles. this research was supported by national science foundation of china grants nsfc 41702002 and 41872008; and the state key laboratory of palaeobiology and stratigraphy (nanjing institute of geology and palaeontology, cas) 193111. vertebrate diversity trends and chrono-, litho-, chemo-, and cyclostratigraphy of the late cretaceous manitoba escarpment in saskatchewan and manitoba, canada aaron a. kilmury1, michelle p.b. nicolas2, and kirstin s. brink1 1department of geological sciences, university of manitoba, winnipeg, mb, canada; kilmurya@myumanitoba.ca; kirstin.brink@umanitoba.ca 2manitoba geological survey, winnipeg, mb, canada; michelle.nicolas@gov.mb.ca stratigraphic correlations of late cretaceous western interior seaway (wis) deposits of the manitoba escarpment with coeval deposits across north america have proven historically challenging due to poor surface exposures and the repeating nature of calcareous and non-calcareous, massive mudstone units bound by unconformable contacts. stratigraphic work over the last two decades, including an improved lithostratigraphic framework, radiometric ages of several horizons, chemostratigraphic profiles of drillcore, and timing and duration estimates of transgressive-regressive mega cycles, have significantly improved the accuracy of regional correlations. a correlation chart consisting of several types of stratigraphic profiles was constructed and correlated with recently estimated trends of vertebrate generic diversity in order to provide insight into potential relationships between changes in relative sea level and vertebrate diversity over a broad temporal range (cenomanian-maastrichtian) from a biogeographically important, north-central locality along the wis eastern margin. transgressive-regressive mega cycles are recognized in the lithoand chemostratigraphic profiles of the upper cretaceous deposits in manitoba. deposition of lithologic units with the highest estimates of vertebrate generic diversity, the cenomanian belle fourche and early campanian pembina members, respectively coincide with an unnamed mega cycle referred to here as the belle fourche mega cycle and the claggett mega cycle. a significant change in community structure is also apparent between the shark-dominated communities of the belle fourche mbr and the marine reptile-dominated communities of the lower pembina mbr. differences of average water depth between the mid-cenomanian and early campanian wis could partially explain the apparent change in vertebrate community structure. other likely contributing factors to the difference in community structure include the feeding habits of apex predators, with mainly piscivorous sharks and pliosaurs dominant in the mid-cenomanian and mosasaurs with comparatively more diverse feeding habits dominant in the early campanian. taken together, these data are helping to elucidate the dynamics of community structure in the wis through time. vertebrate anatomy morphology palaeontology 9:1–39 26 the internal cranial anatomy of panoplosaurus mirus (dinosauria: nodosauridae) marissa c.h. livius1, hillary c. maddin1, michael j. ryan1, 2, and jordan c. mallon1, 3 1department of earth sciences, carleton university, 1125 colonel by drive, herzberg laboratories, ottawa, on, k1s 5b6, canada; marissalivius@cmail.carleton.ca; hillary.maddin@carleton.ca; michaelj.ryan@carleton.ca 2palaeobiology section, canadian museum of nature, po box 3443, station d, ottawa, on, k1p 6p4, canada 3beaty centre for species discovery and palaeobiology section, canadian museum of nature, po box 3443, station d, ottawa, on, k1p 6p4, canada; jmallon@nature.ca the heavily armoured and hyperossified skulls of ankylosaurs have presented challenges for the description of their internal anatomy which is, therefore, poorly known. the quality of data that can be obtained using computed tomography (ct) imaging has increased in recent years, providing a valuable tool for examining endocranial features that are otherwise inaccessible. even so, highly detailed endocranial descriptions are available for only a very few ankylosaurid ankylosaurs; data for the sister clade, nodosauridae, are also scarce. here we present a digital reconstruction and description of the holotype skull for panoplosaurus mirus (cmn 2759) and compare it to published data for other ankylosaur taxa. preliminary results reveal that the endocast of cmn 2759 exhibits a less pronounced flexure between the main structures of the brain (forebrain, midbrain, and hindbrain) than has been reported in other nodosaurids and more closely resembles those of ankylosaurids. we also found convoluted nasal passages with distinct rostral and caudal loops that correspond to those described for the nodosaurid specimen rom 1215 (variably attributed to panoplosaurus or edmontonia). similarly convoluted nasal passages have also been described for the basal nodosaurid pawpawsaurus campbelli. although the nasal morphology of cmn 2759 is not as complex as that of the ankylosaurid euoplocephalus tutus, this specimen demonstrates that highly sophisticated nasal passages were also present and more complex in nodosaurids than previously reported. these findings provide the first insights into the endocranial anatomy of panoplosaurus mirus, and will facilitate comparisons with other ankylosaurs to assess both systematic and paleobiological trends within ankylosauria. first record of a parasaurolophin hadrosaur from the oldman formation of southern alberta bradley d. mcfeeters1, david c. evans2,3, michael j. ryan1, and hillary c. maddin1 1department of earth sciences, carleton university, 1125 colonel by drive, ottawa, on, k1s 5b6, canada; bradleymcfeeters@cmail.carleton.ca; michaelj.ryan@carleton.ca; hillary.maddin@carleton.ca 2department of natural history, royal ontario museum, 100 queen’s park, toronto, on, m5s 2c6, canada 3department of ecology and evolutionary biology, university of toronto, 25 willcocks street, toronto, on, m5s 3b2, canada; d.evans@utoronto.ca hollow-crested hadrosaurs (hadrosauridae: lambeosaurinae) are well represented in the dinosaur park formation of alberta, but are poorly known from older units, including the underlying oldman formation (upper cretaceous: campanian). a new braincase from the comrey sandstone (middle unit) zone at the milk river ridge reservoir locality in southern alberta represents the first diagnostic cranial material of an adult canadian society of vertebrate palaeontology 2021 abstracts 27 lambeosaurine from the oldman formation. it shares with other lambeosaurines an anteroposteriorly short parietal and short supraoccipital-exoccipital shelf. derived characters shared with parasaurolophus include a thickened and steeply angled frontonasal contact, and the wide angle of the anterior frontals without a median cleft, allowing for the identification of the first definitive record of parasaurolophini in the oldman formation. however, in contrast to a previously described adult parasaurolophus braincase from the dinosaur park formation, the nasal contact of the frontal lacks the pronounced posterodorsal extension that underlies the posteriorly projecting crest. the posterior margin of the contact has only a small vertical projection, resembling the condition described in juvenile parasaurolophus, despite the large size and fused interfrontal contact of the milk river ridge reservoir braincase, indicating its adult ontogenetic status. this difference may be attributable to heterochrony, with the ancestral adult development of the nasofrontal contact being attained in the juvenile stage of the stratigraphically higher form. as one of the stratigraphically lowest records of the clade parasaurolophini, the milk river ridge reservoir specimen is a significant source of new information concerning the timing and process of this clade’s phylogenetic and morphological divergence from other derived lambeosaurines. palaeobiodiversity statistics and paleoenvironmental implications of microvertebrate localities from the frenchman formation (latest cretaceous, maastrichtian) of saskatchewan, canada jack r. milligan1, and emily l. bamforth1,2 1department of geological sciences, university of saskatchewan, saskatoon, sk, s7n 5e2; jrm451@mail.usask.ca 2royal saskatchewan museum, t. rex discovery centre, eastend, sk, s0n 0t0; emily.bamforth@gov.sk.ca the latest mesozoic rocks of chambery coulee in southwest saskatchewan have offered insight into the paleobiodiversity and paleoenvironment leading up to the end-cretaceous (k-pg) mass extinction event. the late maastrichtian (lancian) frenchman formation, coeval with the hell creek and lance formations in the usa contain a mixture of fluvial-floodplain and terrestrial paleoenvironments less than 20 m below the k-pg boundary. these strata are well-known for producing notable specimens of large trionychid turtles, as well as large non-avian dinosaurs including a large specimen of tyrannosaurus rex (rsm p2523.8) from chambery coulee. within the vicinity of the t. rex site, there are microvertebrate fossil localities that contain an assemblage of taxa useful in paleoecological studies. here we present the alpha and beta diversity statistics from several microvertebrate sites found within chambery coulee including the ‘kangaroo down,’ ‘bingo,’ ‘hairpin,’ and ‘west-point’ sites. analysis of the sedimentary stratigraphy and biodiversity statistics were integrated together to determine the paleobiodiversity patterns of these microvertebrate sites and how the paleoenvironment reflects patterns of diversity at the regional level of chambery coulee immediately prior to the k-pg mass extinction event. a ~9.5 m stratigraphic section at the kangaroo down site was correlated with previously studied sections at hairpin, bingo, and west-point. the kangaroo down and bingo sites are higher in section than the hairpin and westpoint sites with the former being interpreted as low energy inland fluvial environments and the latter being interpreted as higher energy coastal environments. raw abundance data were used to calculate alpha diversity indices including chao-1 and jackknife-2, and occurrence data were used to calculate beta diversity indices including the bray-curtis similarity and whittaker’s global beta diversity. when we compare the statistics of each of the chambery coulee microvertebrate sites, we find a high diversity of microvertebrates represented across all the vertebrate anatomy morphology palaeontology 9:1–39 28 sites we studied after accounting for preservation bias and collection methods. the kangaroo down and bingo sites appear to include a high abundance and greater occurrence of terrestrial taxa including salamander and trionychids (soft-shelled turtles), and semiaquatic taxa including champsosaurus, whereas the hairpin and westpoint sites seem to include a high abundance and higher occurrence of aquatic taxa including myledaphus and lepisosteus. this suggests that paleobiodiversity statistics including alpha and beta diversity based on abundance and occurrence data can be used as a probable measure for discerning microhabitats at stratigraphically similar microvertebrate sites within a larger paleoenvironment. this will help elucidate biodiversity patterns across a wide range of taxa in chambery coulee during the time just before to the k-pg mass extinction event. a bird coracoid from the horseshoe canyon formation (earliest maastrichtian) of alberta, canada sydney r. mohr1, gregory f. funston2, and thomas a. stidham3 1department of biological sciences, university of alberta, edmonton, ab, canada; smohr@ualberta.ca 2school of geosciences, university of edinburgh, edinburgh, uk; gregory.funston@ed.ac.uk 3key laboratory of vertebrate evolution and human origins of the chinese academy of sciences, institute of vertebrate paleontology and paleoanthropology, chinese academy of sciences, beijing, china; presbyornis@gmail.com a new fragmented left avian coracoid represents the first confirmed avian skeletal element from the early maastrichtian (71.8–71.5 ma) of the horseshoe canyon formation of alberta, canada. this specimen also represents one of the largest fossil bird coracoids found in the province. a number of features, including a prominent acrocoracoid process and a well-defined procoracoid process, places this specimen within the ornithurae. in addition to several neornithine-like features, it retains numerous ornithurine plesiomorphies, and this mosaic of traits indicates it is unlikely to represent a neornithine bird. as its fragmentary nature prevents a specific diagnosis, we therefore refer to it here as ornithurine h (ualvp 59403). this specimen bears particular resemblance to four unassigned ornithurine coracoids from other campanian and maastrichtian localities in north america, all of which share numerous distinctive traits not found in other contemporaneous ornithurine coracoids. these include a shallow and weakly-defined triangular scapular cotyle, a humeral articular facet positioned lateral to the scapular cotyle, and a prominent, hooked procoracoid process. however, several features including its larger body size (~3.0 kg), a large supracoracoideus nerve foramen situated midway on the coracoid shaft, and a dorsally-projecting caudal rim of the scapular cotyle distinguish this specimen from other coracoids and indicate that ornithurine h likely represents a new taxon. the projecting rim of the cotyle and laterally-oriented humeral articular facet are also present in the coracoid of the turonian ornithurine ichthyornis dispar, underscoring the distinct combination of features that characterizes ornithurine h. whereas this new specimen adds to the growing list of north american fossil birds represented primarily by isolated and incomplete material, it nevertheless expands on our understanding of early maastrichtian paleobiodiversity in alberta, and provides further evidence of a widespread and diverse assemblage of ornithurine birds throughout the late cretaceous of north america. canadian society of vertebrate palaeontology 2021 abstracts 29 a quantitative analysis of morphological variation in dentition among thescelosauridae with implications for thescelosaurid palaeoecology, macroevolution, and microsite identification nathaniel e.d. morley1, michael naylor hudgins1, caleb m. brown2, philip j. currie1, han feng-lu3,4, and corwin sullivan1,5 1department of biological sciences, university of alberta, edmonton, ab, t6g 2e9, canada; nmorley@ualberta.ca, hudgins@ualberta.ca, pjcurrie@ualberta.ca, corwin1@ualberta.ca 2royal tyrrell museum of palaeontology, drumheller, ab, t0j 0y0, canada; caleb.brown@gov.ab.ca 3school of earth sciences, china university of geosciences, wuhan, 430074, china; hanfl@cug.edu.cn 4key laboratory of evolutionary systematics of vertebrates, institute of vertebrate paleontology and paleoanthropology, chinese academy of sciences, beijing, 100044, china; hanfl@cug.edu.cn 5philip j. currie dinosaur museum, wembley, ab, t0h 3s0, canada; corwin1@ualberta.ca thescelosauridae is a poorly studied clade of small, herbivorous ornithischians that existed from the aptian until the end of the cretaceous in asia and western north america. although fossils of these gracile taxa are generally rare, isolated thescelosaurid teeth are common at microfossil sites. however, due to their generalized morphology, their teeth are easily confused with those of other contemporaneous small-bodied ornithischians. we use twelve linear measurements to document morphometric variation among the unworn, heterodont teeth of various thescelosaurid taxa based on teeth preserved in identifiable skeletons of haya griva, jeholosaurus shangyuanensis, parksosaurus warreni, thescelosaurus neglectus, thescelosaurus sp. (sdsm 7210; formerly bugenosaura), and zephyrosaurus schaffi. in a principal components analysis (pca) of the measurements, pc1 and pc2 accounted for 77% and 12% of the total variation, respectively. in a canonical variates analysis (cva), cv1 and cv2 explained 73% and 12% of the separation among the groups, respectively, and an associated confusion matrix correctly classified 92% of the teeth. this accurate confusion matrix classification holds promise for the identification of isolated thescelosaurid teeth using morphometrics. a permanova showed statistically significant separation among thescelosaurid taxa (f = 3.72, p(a) > 0.01). in both the pca and the cva, p. warreni, t. neglectus, t. sp. and z. schaffi clustered closely together with significant overlap among the premaxillary, maxillary, and dentary teeth. however, the premaxillary teeth of h. griva and maxillary teeth of j. shangyuanensis formed discrete clusters on the same plots. the morphometric overlap among the north american taxa (p. warreni, t. neglectus, t. sp. and z. schaffi) suggests that they may have shared similar feeding strategies and dietary preferences. in contrast, the disparate morphologies of the asian taxa (h. griva and j. shangyuanensis), relative both to the north american taxa and to each other, suggest that they had divergent feeding strategies and dietary preferences. this morphometric analysis should facilitate the identification of thescelosaurid teeth from microsites and the testing of hypotheses on the biogeography, macroevolution, palaeoecology, and temporal distribution of thescelosauridae using microsite data. vertebrate anatomy morphology palaeontology 9:1–39 30 new data on the distal tarsals of ornithomimidae provided by a partially articulated specimen from the kaiparowits formation (late campanian) of southern utah, usa rachel e. nottrodt1 and andrew a. farke2 1department of geoscience, university of calgary, 2500 university dr. nw, calgary, ab, t2n 1n4, canada; rachel. nottrodt@ucalgary.ca 2raymond m. alf museum of paleontology at the webb schools, 1175 west baseline road, claremont, ca, 91711, usa; afarke@webb.org the ankle in non-avian theropod dinosaurs consists of the astragalus and calcaneum proximally and a distal series of tarsal bones capping the metatarsals. nearly all theropod taxa have only two distal tarsals, identified as distal tarsals 3 and 4. historically, the morphology and anatomical relationships of these distal tarsals is uncertain in ornithomimosaurs due to lack of preservation and/or disarticulation, but even in articulated specimens, the bones can be difficult to access. a previously undescribed, partially articulated ornithomimid hind limb fossil from the kaiparowits formation (late campanian) of southern utah, usa, uniquely preserves both distal tarsals completely and in articulation with their surrounding elements. this is the first ornithomimid specimen from north america for which the distal tarsals can be described in comprehensive detail from multiple views. distal tarsal 3 contacts both metatarsals ii and iii, whereas distal tarsal 4 contacts only metatarsal iv. distal tarsal 4 also shows a tab-like process that projects laterally. comparison of the new fossil specimen with other ornithomimosaurs shows that distal tarsals in ornithomimosauria can be generalized as: i) paired, representing distal tarsals 3 and 4; ii) not fused to one another or to the proximal metatarsals; and iii) proximo-distally compressed. furthermore, tarsal morphology and position across ornithomimosauria vary in: i) shape of the posterior surface of distal tarsal 3; ii) antero-posterior position of the distal tarsals relative to the proximal ends of the metatarsals; iii) extent of distal tarsal coverage of the proximal metatarsal surfaces; and iv) presence of a lateral flange on distal tarsal 4. as the first ornithomimid specimen from north america to reveal both the proximal and distal surfaces of both distal tarsals, and one of the very few ornithomimids for which tarsal morphology can be seen in articulation from multiple views, this fossil shows the importance of articulated specimens for tracking tarsal evolution and variation. canadian society of vertebrate palaeontology 2021 abstracts 31 new shallow snouted species of velociraptor sheds light on intraspecific variation in velociraptor mongoliensis and possible niche partitioning between species mark j. powers1, mark a. norell2, and philip j. currie1 1department of biological sciences, university of alberta, cw-405 biological sciences building, edmonton ab, t6g 2e9, canada; powers1@ualberta.ca; pjcurrie@ualberta.ca 2macaulay curator, division of paleontology, american museum of natural history, new york, ny 10024, usa; norell@amnh.org despite being some of the largest representatives of dromaeosauridae, eudromaeosaurians were small to medium sized predators in their respective ecosystems. predatory adaptations such as serrated teeth, recurved claws, and a specialized sickle claw on the end of their second pedal digit would have allowed them to flourish in smallto medium-sized predator niches, as well as providing variability among close relatives. this makes understanding their phylogenetic relationships and morphological disparity of utmost importance to addressing broad scoping questions about dinosaur ecology. unfortunately, in north america the fossil skeletons of dromaeosaurids are generally rare and are largely incomplete when found. this has been largely attributed to preservation biases for large-bodied animals in many depositional environments (particularly fluvial systems). strata with dinosaur fossils in the djadokhta formation of mongolia are represented by aeolian deposits associated with sand accumulation or large dune collapses. within this depositional environment, small-bodied vertebrates are preserved more readily. half a dozen skeletons, varying between 60 to 95% completeness, and numerous more isolated specimens have been collected and assigned to velociraptor mongoliensis. referral of these specimens to v. mongoliensis has been based on general morphological similarity and paleogeographical provenance and variation has been assumed to be intraspecific without any formal analysis. the holotype of v. mongoliensis was discovered at the flaming cliffs locality in mongolia. however, most referred specimens come from further west, at or near the tögrögiin shiree locality. one nearly complete specimen collected from the flaming cliffs locality in 1995 (mpc-d 100/982), has morphological features distinct from all other specimens referred to v. mongoliensis in possessing an antorbital region of the skull (snout) that is distinctly shallow dorsoventrally. examination of the temporal region of the skull and postcranium, reveals at least four features distinct from other specimens referred to v. mongoliensis. these include an anteriorly abbreviated cerebellar fossa with an elongate olfactory canal, a lacrimal notch of the frontal that is more vertically oriented as opposed to transverse in v. mongoliensis, a subvertical ridge on the ilium anterodorsal to the acetabulum. this specimen has been referred to v. mongoliensis in several previous publications and its morphological differences from v. mongoliensis specimens were suggested to be individual variation; however, despite the striking profile of the skull of mpc-d 100/982 no tests of variation were performed. up to 15 linear measurements were taken from velociraptorine and non-velociraptorine eudromaeosaurian maxillae — a highly complex and diagnostic element within eudromaeosaurians — to perform principal component analysis (pca) and examine phenetic clustering within morphospace. the results show that mpc-d 100/982 falls well outside the range of variation observed in other specimens referred to v. mongoliensis. the degree to which mpc-d 100/982 varies from v. mongoliensis specimens is even greater than that observed for the holotype of velociraptor osmolskae (imm99nm-bym-3/3a), supporting the separation of mpc-d 100/982 on a species level. a notable linear spread of v. mongoliensis specimens in the pca shows a positively allometric trend, with smaller specimens plotting more negatively along pc 1 and pc 2 and may represent an ontogenetic shift. to examine possible ontogenetic trends in v. mongoliensis further, linear regressions of individual maxillary variables with a high degree of taxonomic variance (maxillary height, anterior ramus length, antorvertebrate anatomy morphology palaeontology 9:1–39 32 bital fossa length, and lateral lamina height below the antorbital fossa anteriorly) were performed. these features show positive allometry in relation to maxillary length across velociraptor mongoliensis specimens. mpc-d 100/982 does not fit with these trends and falls well outside the 95% confidence regression intervals. mpc-d 100/982 possesses a long antorbital fossa, a distinct maxillary fenestra morphology, and the most elongate (high length/height ratio) snout of any eudromaeosaurian known. discrete morphological characters and morphometric analyses support separating mpc-d 100/982 from v. mongoliensis as representing its own distinct species. variation in the snouts of v. mongoliensis and the new species may have allowed them to have some overlap in home ranges with reduced competition. in modern terrestrial ecosystems, snout shapes are shown to often correlate to preferred prey size. this is most notably demonstrated in canids, a clade with carnivorous members of similar size to most eudromaeosaurians. the advantage of snout shapes in prey capture, for canids and many other vertebrates, is supported by functional morphology studies. such studies have demonstrated that longer jaws are more effective for rapid biting and limited power, whereas stout jaws perform more efficiently in biting and handling. the former being more effective at catching small-bodied, fast-moving prey, while the latter is better for taking prey of larger body size that may put up more of a fight. although we cannot observe the preferred prey of eudromaeosaurians directly, we can use the principles of functional morphology relating to jaw biomechanics, examine the faunal composition of ecosystems containing eudromaeosaurians, and make preliminary hypotheses about drivers for variation in snout shape within the clade through time and space. small-bodied vertebrates are common in the djadokhta formation and the shallow condition in the rostrum of the new species of velociraptor may have been an adaptation for specializing on these prey items. conversely, v. mongoliensis possessed a deeper snout that became deeper as they grew and may have allowed members of this species to have a more diverse diet as suggested by the ‘fighting dinsaurs’ specimen (a protoceratops and v. mongoliensis locked in combat) reconstructing life history of the sabre-toothed cat smilodon fatalis using bone histology ashley r. reynolds royal ontario museum, department of natural history, 100 queen’s park, toronto, on, m5s 2c6, canada, and university of toronto, department of ecology and evolutionary biology, 25 willcocks st, room 3055, toronto, on, m5s 3b2, canada; ashraereynolds@gmail.com the life history strategy (e.g., growth rate, time to maturity) of an organism is a fundamental aspect of its biology that may be correlated with other ecological traits such as the degree of sociality exhibited by a species. however, assessing the life history strategy of extinct vertebrates is difficult because their growth and behaviour must be estimated using limited material, usually hard tissues. osteohistology, the histological study of bone, is increasingly being used by palaeobiologists to study life history strategies in extinct vertebrates (specifically, assessing time to maturity using growth curves), though there has historically been a heavy focus on reptiles. studies of mammalian osteohistology have become more common, but the rigorous mathematical methods for growth curve reconstruction used for reptiles have not been adequately tested in any major mammalian group. the purpose of this study was to test the viability of these methods on extant felids and reconstruct the growth of the sabre-toothed cat smilodon fatalis using osteohistological data. specifically, two hypotheses were tested relating to the palaeobiology of s. fatalis: that it was not as sexually dimorphic as extant felids and that it was social. canadian society of vertebrate palaeontology 2021 abstracts 33 age and weight data were collected from wild and captive individuals from 71 extant species in the carnivoran suborder feliformia, from which growth curves were calculated. additionally, osteohistology of the extant lion (panthera leo) and tiger (panthera tigris), the two extant felids closest in body mass to s. fatalis, were documented. to conduct growth curve reconstruction for s. fatalis, 20 femora from pit 3 of the rancho la brea tar pits were thin sectioned at the minimum circumference of the diaphysis and lines of arrested growth (lags) were counted and their circumferences measured. growth curves for extant feliforms and s. fatalis were created using the bestfit model from the richards family of growth models, as determined using the akaike information criterion. curves generated for extant felids perform well in capturing the overall pattern of growth typical of a species but tend to overestimate body mass at birth. sexual dimorphism in adult body mass is common among extant feliforms, with the predominant mode of sexual dimorphism being male-biased. the age at which adult body mass is reached is positively associated with large adult body mass, while maximum daily growth rate (kg/day) is negatively associated with social behaviour, such that social species like p. leo have a lower maximum daily growth rate than solitary species like p. tigris. collectively, these results suggest that sex differences in body mass and the varying correlates with growth rate should be considered in the analysis of s. fatalis growth. osteohistology of p. leo and p. tigris femora indicate that lines of arrested growth (lags) are deposited during femoral growth and may be reliably used to determine approximate age at death and growth curves. s. fatalis femora classified as juvenile never had more than two lags preserved, and adults had a variable number of lags greater than two. specimens with three or more preserved lags were included in a growth curve reconstruction using a mixed-effects process-error richards growth model. there is a large amount of variation in the adult body mass of the sabre-toothed cat, ranging from 160 to 255 kg, suggesting that these cats may have showed a similar degree of sexual dimorphism in body mass as extant felids. growth periods were prolonged relative to extant big cats, with individuals taking around five years to reach adult body mass. comparatively, asymptotic body mass is reached in p. leo and p. tigris at 2.4 and 1.8 years, respectively. maximum daily growth rates in s. fatalis are lower than in p. leo and p. tigris. this may indicate gregarious social behaviour in the sabre-toothed cat. additionally, such low growth rates and long time to maturity are known to increase risk of extinction in extant animals. this should therefore be explored as a contributing factor to the end-pleistocene extinction of s. fatalis. overall, this study has produced the first growth curve for any fossil carnivoran, and the methods used provide a framework within which the evolution of life history strategies in felids can be examined. identifying competitive exclusion in the vertebrate fossil record: lessons from early vertebrate morphometrics bradley scott and philip anderson 101 shelford vivarium, 608 east healey street champaign, il 61820, usa; brscott2@illinois.edu; andersps@illinois.edu competition with gnathostomes is the most common hypothesis for the extinction of the ostracoderms (janvier 1996; long 2011); however, it is not clear whether competition between clades is even testable in the fossil record (purnell 2001). we review different qualitative and quantitative methods for differentiating competition from alternative hypotheses of extinction and whether competition between gnathostomes and agnathans, specifically, can be rejected using the fossil record. competition in the fossil record is often recognized by the appearance of one taxon followed by the disappearance of another morphologically similar taxon in the same geographic region. as one taxon increases in abundance the other taxon should decrease (tilman 1987; purnell 2001; anderson et al. 2011). explicitly this is competitive exclusion (e.g., krause 1986). competitive exclusion can only include coexistence for an ecologically brief time, because lengthy coexistence of two taxa followed by the disappearance of vertebrate anatomy morphology palaeontology 9:1–39 34 one taxon requires cause beyond presence of the remaining taxon. the problem with hypothesizing competitive exclusion as a cause of extinction is that patterns in the fossil record attributed to competitive exclusion are nearly identical to extinction of an incumbent followed by invasion by a new species (replacement), unless there is fine spatial and temporal resolution of first and last appearance of each taxon. character displacement (changes in each taxon so they are less similar over time) is another method for identifying hypothetical competition between taxa (tyler and leighton 2011); however, character displacement is not suitable as a test of competition as a cause of extinction because it cannot reject predation, environmental changes or other alternative causes of extinction. early vertebrate fossil bearing sequences rarely possess the temporal and spatial resolution necessary to reject replacement or coexistence between taxa, and even partially complete specimens are too rare to test for character displacement. even if alternatives to competition cannot be rejected, rejecting competition may still be feasible. methods for rejecting competition in the fossil record will rely on clear definitions of competition. one challenge is that ecological definitions of competition are rarely explicit and are often broadly inclusive of any negative interactions between two taxa (tilman 1987). in order to create falsifiable criteria for competition with broad utility in this study, we constrain our definition of competition to the following: the use of the same resources (food or habitat) by more than one taxon in the same place at the same time, distinct from predation, bioengineering, or other indirect negative interactions. under this definition, competition between two or more taxa can be rejected if any of the following are true: 1. taxa are not present at the same time, 2. taxa are not present in the same place, 3. taxa do not use the same habitat, or 4. taxa do not consume the same food. identifying criteria 1 and 2 depends on the temporal and spatial resolution of the fossil record. while criteria 3 and 4 can never be known for certain in fossil taxa, they can be estimated using functional morphology and biomechanics. neontological studies have shown competition is often stronger between morphologically similar taxa and weaker between morphologically different taxa (e.g. montoya and burns 2007; adams 2004). if two taxa are sufficiently different from each other, then competition can be rejected. we present preliminary morphometric analysis of ostracoderms and early gnathostomes with discussion of how we intend to establish a standard for morphological difference sufficient to reject competition among early vertebrates. our standard will be based on comparison with ecomorphology in extant sharks (neoselache). by rejecting competition, we can focus on alternative hypotheses, as well as narrow the range of taxa for which extinction due to competition is a plausible hypothesis. literature cited adams, d.c. 2004. character displacement via aggressive interference in appalachian salamanders. ecology 85:3664–3670. anderson, p. s. l., m. friedman, m.d. brazeau, and e.j. rayfield. 2011. initial radiation of jaws demonstrated stability despite faunal environmental change. nature 476:206–209. janvier, p. 1996. early vertebrates. clarendon press, oxford, 408 pp. krause, d.w. 1986. competitive exclusion and taxonomic displacement in the fossil record: the case of rodents and multituberculates in north america; pp. 95–117 in k.m. flanagan, and j.a. lillegraven (eds.). contributions to geology special paper 3, vertebrates, phylogeny, philosophy. university of wyoming, laramie, wy. long, j. 2011. the rise of fishes—500 million years of evolution. 2nd ed. john hopkins university press, baltimore, md, 224 pp. montoya, i., and k.c. burns. 2007. community-wide character displacement in new zealand skinks. journal of biogeography 34:2139–2147. purnell, m. a. 2001. scenarios, selection, and the ecology of early vertebrates; pp. 188–208 in p.e. ahlberg (ed.). major events in early vertebrate evolution. taylor & francis, london, uk. tilman, d. 1987. the importance of the mechanisms of interspecific competition. the american naturalist 129:769–774. tyler, c.l., and l.r. leighton. 2011. detecting competition in the fossil record: support for character displacement among ordovician brachiopods. paleogeography, paleoclimatology, paleoecology 307:205–217. canadian society of vertebrate palaeontology 2021 abstracts 35 a hesperornithiform (avialae: ornithuromorpha) from the upper cretaceous nemegt formation (lower maastrichtian) in mongolia tomonori tanaka1, 2, yoshitsugu kobayashi3, yuong-nam lee4, robin sissons5, michael ryan6, tsogtbaatar chinzorig7, and khishigjav tsogtbaatar8 1tamba dinosaur fossil lab, 1110, tanigawa, sannan, tamba, hyogo, japan; tomotanaka2020@gmail.com 2university of hyogo, yayoigaoka 6, sanda, hyogo, japan 3hokkaido university museum, kita10, nishi 8, sapporo, hokkaido, japan; ykobayashi@museum.hokudai.ac.jp 4seoul national university, bldg #25-1, rm #510, 1 gwanak-ro, gwanak-gu, seoul, korea; ynlee@snu.ac.kr 5university of alberta, edmonton, alberta, t6g 2e9, canada; robin.sissons@gmail.com 6carleton university, 2115 herzberg laboratories, ottawa, ontario, k1s 5b6, canada; michaelj.ryan@carleton.ca 7north carolina state university, 121 west jones street, raleigh, north carolina, 27601, usa; ctsogtb@ncsu.edu 8institute of paleontology of mongolian academy of sciences, chingeltei district-4, sambuu street, ulaanbaatar-14201, mongolia; tsogtmondin@gmail.com. hesperornithiforms have been predominantly reported from the marine cretaceous deposits of the western interior seaway of north america, although sparse records of this group have also been reported from fluvial deposits in asia and north america especially from the maastrichtian. because asian hesperornithiform fossils are extremely rare compared to north american specimens, the diversity of asian taxa remains unclear. here, we report a complete right tibiotarsus (kid 310) of a hesperornithiform from the inner continental fluvial deposits of the nemegt formation (lower maastrichtian) in the gobi desert of southwestern mongolia, which was collected in 2008 during the korea-mongolia international dinosaur expedition. the proximal tarsals (the astragalus and the calcaneum) are completely fused to the distal epiphysis, indicating that it is an adult individual. it has a fibular crest extending to the mid-shaft and a laterally angled proximolateral articular surface. these characters are only seen in hesperornithiformes. a shallow tibial incision further suggests the specimen can be assigned as a non-hesperornithid hesperornithiform. although the phylogenetic position of kid 310 within the clade of hesperornithiformes is ambiguous due to its preservation as an isolated bone, it presents unique morphological characters such as the lateral margin of the cnemial crest being pointed and expanded laterally, and the fibular crest being remarkably expanded laterally. however, it is not clear if it is a new taxon because two other hespeornithiforms (judinornis nogontsavensis and brodavis mongoliensis) from the same formation do not preserve the tibiotarsus. the body size of kid 310 is estimated to have been similar to that of brodavis mongoliensis, which is one of the smallest hesperornithiforms known. inland hesperornithiforms in the maastrichtian such as judinornis nogontsavensis, brodavis mongoliensis, brodavis americanus, and brodavis baileyi have smaller body sizes in comparison to the contemporary taxa from marine deposits (e.g., asiahesperornis sp. and canadaga sp.), indicating that hesperornithiform body sizes maybe related to their habitat environment (freshwater or marine). vertebrate anatomy morphology palaeontology 9:1–39 36 a kinetic model of the palaeognath ribcage with implications for understanding avian ventilation yan-yin wang1 and corwin sullivan1,2 1department of biological sciences, university of alberta, edmonton, ab, t6g 2e9, canada; yanyin@ualberta.ca; corwin1@ualberta.ca 2philip j. currie dinosaur museum, wembley, ab, t0h 3s0, canada, in respiratory biology, ventilation is typically regarded as the process of transporting gas between the respiratory organ and the external environment. scholars have acquired extensive knowledge of many aspects of ventilation in archosaurs, including the anatomy of respiratory organs, the activity patterns of relevant muscles, and the kinematics of the ribcage during ventilation. however, the kinetic forces and moments involved in ventilation have been addressed in few studies, and most of these have been two-dimensional in scope and have focused on only a portion of the thorax. a three-dimensional kinetic model can examine the thorax comprehensively and has the potential to incorporate knowledge from other studies of respirations. here we present a kinetic model of the paleognathic ribcage to represent the condition of the flightless birds. the skeletal elements were created by scanning the disarticulated thoracic bones of an ostrich using a flexscan 3d surface scanner. the model was set up for analysis in autodesk maya and simm (software for interactive musculoskeletal modelling). the kinematics of skeletal elements were described in terms of three kinematic rotations (‘caliper’, ‘bucket handle’, and ‘pump handle’) around the relevant joint centres, whose positions and orientations could only be estimated but were consistently positioned using anatomical landmarks in both maya and simm. the muscles of the left thorax were modelled as a total of 122 muscle vectors, based on dissection of an emu and avian anatomical literature . most hypaxial muscles have broad insertions on the ribs and cannot be accurately represented as single vectors. instead, individual muscles were modelled as multiple vectors spaced throughout the area of insertion, with each vector representing a bundle of similarly oriented fibres. muscle properties used in the model were based on data from human studies, as comparable information was not available for avians. when a single skeletal element moves relative to the rest of the ribcage, the kinetic model indicates that some muscles undergo substantial changes in moment arms which influences the efficiency of the muscles at rotating the rib segments. overall, muscle moment arms change according to non-linear curves (e.g., hyperbola, hyperbolic tangent) as joint rotation occurs. for a given vertebral rib, the moment arms of some muscles (e.g., mm intercostales externi) follow similar curves for all three kinematic rotations, but for other muscles (e.g., m levator costarum) the three types of rotation cause moment arms to change in distinct ways. for a given m intercostalis connecting two adjacent vertebral ribs, the moment arms change sign (and therefore the direction of the angular acceleration) at different stages of rib rotation. the moment arm curves for some muscles suggest they may not function exclusively in inspiration or in expiration, as previously indicated by experimental studies of caiman crocodilus and gallus domesticus. however, the moment arm curves for mm appendicocostales suggest these muscle slips are solely inspiratory, which agrees with previous studies. moment arm curves for mm appendicocostales resemble those for mm intercostales externi, suggesting that mm appendicocostales may have originated as distinct slips of mm intercostales externi like those present in crocodylians. examinations of the muscle moment arms suggest that m. appendicocostalis in paleognathes inherited from their archosaur ancestors may have originated to improve the efficiency in avian ventilation in response to high metabolic demands. refining the current kinetic model should provide further insights into the drivers of ventilatory motions. furthermore, applying this modelling approach to other archosaurs may shed light on the evolution of ventilation in this major amniote group. canadian society of vertebrate palaeontology 2021 abstracts 37 taxonomy of a new goniopholidid specimen from the upper jurassic morrison formation and their diversity in north america junki yoshida1, atsushi hori1, yoshitsugu kobayashi1, michael j. ryan2, yuji takakuwa3, and yoshikazu hasegawa3 1hokkaido university, sapporo, hokkaido, japan; junkiyoshida9@gmail.com; ykobayashi@museum.hokudai.ac.jp 2carleton university, ottawa, ontario, canada; michaelj.ryan@carleton.ca 3gunma museum of natural history, tomioka, gunma prefecture, japan; takakuwa@gmnh.pref.gunma.jp; hasegawa@ gmnh.pref.gunma.jp goniopholididae is a group of basal neosuchians found in the northern hemisphere during the jurassic and early cretaceous, and is closely related to the clade of paralligatoridae and eusuchia. goniopholididae is the earliest crocodyliform group to acquire the modern crocodylian body plan and an inferred semi-aquatic lifestyle. understanding the anatomy, phylogeny, and functional morphology of this group is important for revealing the origin of the modern crocodylian body plan (e.g., platyrostrum and secondary palate) and lifestyle. here we describe a well-preserved, nearly complete skeleton of a goniopholidid (gmnh-pv229), discovered from the sandstone of the brushy basin member of the upper jurassic morrison formation at the east camarasaurus quarry, wyoming, usa, in 1993, and examine its phylogenetic relationships within the family. although most of the cranial and neurocentral sutures of the caudal vertebrae are fused, the cervical, dorsal, and sacral vertebrae remain unfused, indicating the immaturity of the individual at death. the rostral skull length (preorbital length) is 42 cm, one of the largest in goniopholidids, and 60% of the skull length, indicating a medium long rostrum. the ratio of rostral width at the midpoint of the maxilla to the skull width is 0.64, while other goniopholidids (e.g., a. stovalli) show a ratio of less than 0.5. the number of subfossae in the maxillary depression is five as in goniopholis simus, while it is four in amphicotylus lucasii and three in goniopholis kiplingi and anteophthalmosuchus hooleyi. posterior to the nasopharyngeal passage, the pterygoid has a small, shallow, rectangular-shaped postchoanal fossa that is not perforated or connected to the passage and sinus. our data matrix for the phylogenetic analyses was composed of 486 characters and 102 ingroup and one outgroup (gracilisuchus) taxa, including gmnh-pv229. a heuristic search was performed to obtain the most parsimonious trees using paup v. 4.0a. our initial analysis produced 2592 most parsimonious trees with tree lengths of 2400. strict consensus trees in both analyses place gmnh-pv229 within goniopholididae. a sister-taxa relationship of gmnh-pv229 and amphicotylus stovalli is supported by four synapomorphies: the anterior end of the frontal is posterior to the prefrontal, the palatal shelves of the palatines do not fully contact at the mid-line, the anterior border of the internal naris is positioned anterior to the suborbital fenestra, and the internal choana is lanceolated. however, gmnh-pv229 differs from amphicotylus stovalli in having a broad rostrum, a straight lateral border of the nasals, a rounded anterior margin of the palatine, and lacking ‘crest c’ on the ventral surface of the quadrate. gmnh-pv229 has a unique combination of the following features: broad rostrum, five subfossae in the maxillary depression, anterior projection at the posterior margin of the naris, triangular palpebral, lack of ‘crest c’ on the quadrate, presence of postchoanal fossa, perichoanal fossa being wider than the nasopharyngeal passage, and the posterior border of the internal choana located at the midpoint of the pterygoid. these characters suggest that gmnh-pv229 is a new species of amphicotylus. our results show a greater diversity of goniopholidids than previously known in the upper jurassic morrison formation, which currently comprises eutretauranosuchus, amphicotylus stovalli, and a. lucasii, by adding the taxon represented by gmnh-pv229. gmnh-pv229 is characterized by its broad rostrum, suited for feeding on vertebrate anatomy morphology palaeontology 9:1–39 38 large and agile prey, as in some derived cretaceous goniopholidids such as goniopholis simus, goniopholis kiplingi, and anteophthalmosuchus hooleyi. we infer that a broad rostrum may have evolved much earlier than previously suggested within goniopholidids for feeding on large, highly mobile animals in the freshwater environment. how to make monsters: cladistic analysis of ontogeny recovered evidence of anagenesis in north american tylosaurines amelia r. zietlow richard gilder graduate school – american museum of natural history, 200 central park west, new york, ny 10024, usa; azietlow@amnh.org mosasaurs were large, globally distributed aquatic lizards that lived during the late cretaceous. despite numerous specimens of varying maturity, a detailed growth series has not been proposed for any mosasaur taxon. tylosaurus is a genus of particularly large mosasaurs with long, edentulous anterior extensions of the premaxilla and dentary that lived in europe and north america during the late cretaceous (90 to 66 million years ago). three taxa—tylosaurus proriger, t. kansasensis, and t. nepaeolicus—have robust fossil records with specimens spanning a wide range of sizes. furthermore, because they lived in the same place and at the same time, and t. kansasensis are generally smaller than t. nepaeolicus, previous work has hypothesized that they are a single taxon, and t. kansasensis are juveniles. therefore, these species are ideal for testing hypotheses of ontogeny, synonymy (t. kansasensis with t. nepaeolicus), sexual dimorphism, anagenesis, and heterochrony. fifty-nine hypothetical growth characters were identified, including size-dependent, size-independent, and phylogenetic characters. quantitative cladistic analysis was used to recover a growth series for each taxon: t. proriger, 23 specimens and 17 growth stages (consistency index = 0.6, homoplasy index = 0.4); and t. nepaeolicus/ kansasensis, 19 specimens and 12 growth stages (consistency index = 0.6, homoplasy index = 0.4. the results supported the synonymy of t. kansasensis with t. nepaeolicus and that t. kansasensis are juveniles of t. nepaeolicus. a spearman rank-order test resulted in a significant (p < 0.05) correlation between size (skull length and quadrate height) and maturity for both taxa, and evidence for skeletal sexual dimorphism was not found. eleven growth characters, including the development of a knob-like rostrum and increase in quadrate height relative to skull length, were shared by both taxa. finally, a novel hypothesis of anagenesis (i.e., evolution within a single lineage) in western interior seaway tylosaurus species, driven by peramorphy (extension of growth), was tested and supported by a third cladistic analysis including specimens of both t. proriger (15 specimens) and t. nepaeolicus/kansasensis (13 specimens), which recovered evidence of intermediate morphologies in both taxa and peramorphy of skull size and development in t. proriger. canadian society of vertebrate palaeontology 2021 abstracts 39 many thanks to csvp 2021 virtual local organizing committee members: bassel arnaout emily bamforth julien divay annie mcintosh hallie street yan-yin wang thanks also to the following people who served as abstract reviewers: hoai-nam bui james campbell nicola howard sydney mohr vertebrate anatomy morphology palaeontology issn 2292-1389 vertebrate anatomy morphology palaeontology is an open access journal http://ejournals.library.ualberta.ca/index.php/vamp article copyright by the author(s). this open access work is distributed under a creative commons attribution 4.0 international (cc by 4.0) license, meaning you must give appropriate credit, provide a link to the license, and indicate if changes were made. you may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use. no additional restrictions — you may not apply legal terms or technological measures that legally restrict others from doing anything the license permits. published 13 may, 2023 editors: alison m. murray, robert b. holmes, and mark j. powers © 2023 by the authors doi 10.18435/vamp29391 meeting logo design: many thanks to ashan ayanarajan for creating our 2023 csvp logo! this year’s csvp meeting logo is courtesy of carleton university msc student ashan ayanarajan. the logo features the skull of a beluga whale (delphinapterus leucas) over a backdrop of the ancient champlain sea (ca. 10,000 years ago). beluga fossils from this time have been throughout eastern ontario and southern quebec, including in the ottawa area. canadian society of vertebrate palaeontology 2023 abstracts 3 11th annual meeting canadian society of vertebrate palaeontology may 24–26, 2023 ottawa abstracts vertebrate anatomy morphology palaeontology 11:1–41 4 acknowledgements many thanks to csvp 2023 local organizing committee members of the canadian museum of nature: danielle fraser marisa gilbert tetsuto miyashita jordan mallon shyong en pan scott rufolo xiao-chun wu thanks also to the following people who served as abstract reviewers: mark powers colton coppock emily bamforth ashan ayanarajan joshua wasserlauf trystan warnock-juteau denny maranga michael thompson greg funston ryan wilkinson taia wyenberg-henzler christiana garros misha whittingham howard huynh lea veine-tonizzo khoi nguyen aaron dyer henry sharpe tom dudgeon talia lowi-merri danielle fraser canadian society of vertebrate palaeontology 2023 abstracts 5 table of contents horn size variation with latitude in bison bison ashan ayanarajan, danielle fraser, and jordan mallon ........8 middle and late cretaceous forests of northern alberta: new fossils and new insights into boreal dinosaur paleoecology emily l. bamforth ........8 discovery of a new permian ichnofossil assemblage from les iles-de-la-madeleine louis-philippe bateman, hans c.e. larsson, jérôme dubé, dirley cortés, andré mueller, and richard cloutier ........11 revisiting caudal vertebral fusion in mosasaurs (squamata: mosasauridae) using paleohistology: functional implications michael e. burns, jun ebersole, and sahara gonzalez ........12 first pleistocene tetraodontid fish (teleostei, tetraodontiformes) from tanegashima island, japan mori chida and yoshitaka yabumoto ........12 comparison of the efficacy of 2d and 3d tooth shape morphometrics for predicting the diets of carnivorous mammals brigid e. christison and danielle fraser ........13 immature daspletosaurus (tyrannosauridae, tyrannosaurinae) material from the dinosaur park formation of alberta, canada colton c. coppock, mark j. powers, jared t. voris, and philip j. currie ........14 a new pliosaur from the early cretaceous paja formation of colombia: insights into the diversification of brachaucheniinae dirley cortés, mary luz parra-ruge, alexandre demers-potvin, and hans c.e. larsson ........14 habitat heterogeneity and ape evolution in the early miocene of eastern africa susanne m. cote, alan l. deino, david l. fox, john d. kingston, rahab n. kinyanjui, william e. lukens, laura m. maclatchy, kieran p. mcnulty, daniel j. peppe, james b. rossie, and caroline a.e. strömberg ........15 first definitive occurrence of centrosaurus apertus in saskatchewan reported from a multigeneric bonebed within the easternmost outcrop of the dinosaur park formation alexandre v. demers-potvin, emily l. bamforth and hans c.e. larsson ........17 disparate life histories contributed to the palaeocene rise of eutheria gregory f. funston, sofia holpin, sarah l. shelley, thomas e. williamson, and stephen l. brusatte ........18 mosasaur feeding ecology of the bearpaw formation, alberta, canada: the final chapter femke m. holwerda ........18 comparative dental microwear analyses of north american ursids to infer the dietary palaeoecology of extinct pleistocene short-faced bears from the yukon howard m. huynh, prieyankaa nirmalan, and danielle fraser ........19 size reduction in beringian equus throughout the late pleistocene leading up to their extinction zoe landry, clément p. bataille, and danielle fraser ........20 vertebrate anatomy morphology palaeontology 11:1–41 6 sense and sensibility: estimating the hearing capability of otophysan fish and implications for their fossil relatives juan liu ........20 the timing and ecological evolution of modern ant lineages elyssa loewen, caelan libke, christine sosiak, phillip barden, christopher somers, and ryan c. mckellar ........21 a petrified struggle for survival from the lower cretaceous deposits of china jordan c. mallon, gang han, aaron j. lussier, xiao-chun wu, robert mitchell, and ling-ji li ........22 insights and limitations in reconstructing the musculature and skeletal arrangement of the foot in tyrannosaurids and other non-avian theropod dinosaurs annie p. mcintosh, corwin sullivan, john acorn, and philip j. currie ........22 bioerosion trace fossils on triceratops bones from the latest cretaceous frenchman formation, southwestern saskatchewan, canada jack r. milligan, emily l. bamforth, luis a. buatois, and m. gabriela mángano ........24 the head, heart, and fins of a jawless stem gnathostome tetsuto miyashita, michael i. coates, kristen tietjen, pierre gueriau, and philippe janvier ........25 a juvenile pachycephalosaur (dinosauria: ornithischia) skeleton from the upper maastrichtian frenchman formation of saskatchewan, canada bryan r.s. moore, david c. evans, michael j. ryan, r. timothy patterson, and jordan c. mallon ........25 a multivariate comparison of the vertebrate faunas of the horseshoe canyon and wapiti formations of alberta, canada with implications for vertebrate biogeography nathaniel e.d. morley, lindsey r. leighton, eva b. koppelhus, and philip j. currie ........26 identification of acanthomorph diversity in microvertebrate fossil sites alison m. murray and donald b. brinkman ........27 madtsoiidae: monophyletic clade or grouping of convenience? mark j. powers, fernando f. garberoglio, and michael w. caldwell ........28 vertebral pathology: a primer addressing its definitive features in the paleontological record bruce rothschild ........28 a small early permian parareptile with a lateral temporal fenestra from richards spur, oklahoma dylan rowe, erin beauchesne, joseph bevitt, and robert reisz ........29 a plesiosaur representing the first published vertebrate material from the foraminifera-dominated peace river formation, alberta, canada maximilian scott ........30 duck-faced and eagle-eyed: a well-developed visual system in a high-latitude hadrosaur henry s. sharpe, philip j. currie, and corwin sullivan ........31 quantitative reconstruction of feeding mechanics in leptoceratops gracilis brown, 1914 using novel digital methods: a proof-of-concept emilia l. silvestre, louis-philippe bateman, and hans c.e. larsson ........31 new and expanded preparation techniques from pipestone creek material leads to insights about this late cretaceous wapiti formation locality jackson sweder, emily l. bamforth, and maximilian scott ........33 canadian society of vertebrate palaeontology 2023 abstracts 7 changes in emplacement pattern and organization of the palatal dentition accompanied the evolution of herbivory in edaphosauridae (synapsida, eupelycosauria) andrew l. traynor, aaron r.h. leblanc, and kenneth d. angielczyk ........34 evaluation of enamel microstructures in small theropod dinosaurs ashley verstraete, derek w. larson, and kirstin s. brink ........35 redescription of a juvenile hadrosaurid from the upper cretaceous of alberta using computed tomography trystan m. warnock-juteau, michael j. ryan, r. timothy patterson, and jordan c. mallon ........36 isotope palaeoecology of duck-billed dinosaurs (ornithischia: hadrosauridae) from the upper campanian dinosaur park formation joshua wasserlauf, jordan mallon, thomas cullen, françois therrien, brian cousens, and clément bataille ........37 a new archosaurian skeleton from the middle triassic of china: shedding light on the phylogenetic position of wangisuchus (pseudosuchia, gracilisuchidae) xiao-chun wu, zhi-shuai kang, li-yang dong, jian-ru shi, and hai-lu you ........38 hadrosaurid skull from the wapiti formation preserves evidence of new feeding behaviours in tyrannosaurids taia c.a. wyenberg-henzler, nicolas e. campione, phil r. bell, and corwin sullivan ........39 investigating genetic mechanisms of early limb development in ambystoma mexicanum and xenopus laevis jeffrey a. yee, tetsuto miyashita, and hillary c. maddin ........40 vertebrate anatomy morphology palaeontology 11:1–41 8 horn size variation with latitude in bison bison ashan ayanarajan1,2, danielle fraser1,2,3, and jordan mallon1,2 1palaeobiology, canadian museum of nature, po box 3443 stn “d,” ottawa, on, k1p 6p4, canada, dfraser@nature. ca, jmallon@nature.ca, ashanayanarajan@cmail.carleton.ca 2 department of earth sciences, carleton university, 1125 colonel by dr, ottawa, on k1s 5b6, canada. 3department of biology, carleton university, 1125 colonel by dr, ottawa, on k1s 5b6, canada. ecometrics is a method used to evaluate the relationship between the observable traits of organisms and environmental parameters. by selecting traits whose structures are tightly related to their functions, and whose functions directly interact with the environment, it is possible to estimate climatic and other environmental parameters (e.g., mean annual temperature, and dominant local vegetation type) from morphology. horns may be one such trait because they are composed of living tissue and have thermoregulatory functions that constrain their morphology; larger horns have a larger surface area through which body heat may be lost to the environment, which can be problematic in colder environments where lost body temperature can prove detrimental—even life-threatening—to the individual. given that increased thermoregulatory demand may ultimately reduce overall fitness, we expect animals from colder environments to possess smaller horns with lower surface areas. this prediction is supported by a correlation between horn size and latitude for 15 species of bovid, with larger horn sizes observed in tropical and smaller horns in temperate regions. however, the phenomenon has never been studied within a species across a continuous latitude. we aim to test for a relationship between horncore size (horncore length, circumference, and surface area) and climate (i.e., mean annual temperature, and precipitation) for the north american bison (bison bison) by analysing their horn morphology across the latitudes of 35°–65°n. although not statistically significant (p = 0.427), preliminary regression analyses suggest a negative correlation between horn size and latitude in b. bison from 50°–55°n and 60°–65°n (n = 37), possibly indicating that b. bison horns may be used as climate proxies for the past. ongoing work is aimed at testing for a relationship of horncore size with mean annual precipitation, temperature, and dominant local vegetation type. middle and late cretaceous forests of northern alberta: new fossils and new insights into boreal dinosaur paleoecology emily l. bamforth philip j. currie dinosaur museum, wembley, ab, t0h 3s0, canada, and department of geological sciences, university of saskatchewan, saskatoon, sk, s7n 5e2, canada; ebamforth@dinomusuem.ca fossil plant assemblages are of critical importance for recreating paleoenvironments and understanding paleoecology. the diversity and nature of paleofloral assemblages can yield information on climate, photoperiod, latitudinal gradients, and seasonality, as well as providing information on the possible diets of animals living concurrently. assemblages of woody angiosperm dicot leaves and gingkoes can also be an invaluable proxy for paleoclimate reconstruction (spicer 2006). herein are described new paleofloral sites from the late cretaceous wapiti formation and the middle cretaceous dunvegan formation, and their implications for understanding paleoecological and paleoenvironmental patterns. canadian society of vertebrate palaeontology 2023 abstracts 9 the late cretaceous (80 – 68ma) wapiti formation of northwestern alberta and northeastern british columbia spans an interval of geologic time from the lower campanian to the upper maastrichtian. the formation is well known for its vertebrate fossils, containing one of densest dinosaur deposits in north america known as the pipestone creek pachyrhinosaurus bonebed. other finds include additional dinosaur bonebeds (e.g., fanti et al. 2015), microvertebrate localities (fanti and miyashita 2009; fanti et al. 2022), dinosaur trackway sites (fanti et al. 2013; enriquez et al. 2022), and soft-tissue preservation (bell et al. 2014). while the dinosaur fossils and trackways have been well studied, the fossil plant deposits of the wapiti formation have received comparatively less attention. the middle cretaceous (96 – 93 ma) dunvegan formation is a package of middle cenomanian-aged rocks from northwest alberta and northeast british columbia. these rocks were deposited in nearshore and estuarine environments along the coast of the western interior sea (burns and vavrek 2014). vertebrate fossils from the dunvegan formation are rare, but include a trionychid turtle (brinkman 2003), shark remains (cook et al., 2008), ankylosaur bone fragments (burns and vavrek 2014; arbour et al. 2020), a sturgeon fish (vavrek et al. 2014) and dinosaur footprints (mccrea et al. 2001). the paleofloral record from the formation is little known, with published references limited to arbour et al.’s (2020) note of leaf fossils in a paper describing ankylosaur fossils from the dunvegan formation of british columbia. herein is described four new paleofloral assemblages from the wapiti formation, collected in 2022, and one from the dunvegan formation, collected in 2016. the first wapiti assemblage, the spring creek paleofloral site, is dominated by the fronds and cones of the conifers metasequoia and parataxodium. common leaves in this assemblage include platanus and menispermities morphotypes, three types of gingko (including an unknown taxon), and a potential water plant (cf. ceratophyllum). the wapiti assemblage at the dc bonebed paleofloral site contains comparatively few gymnosperms and is dominated by broad-leafed angiosperm fossils (colocasia, menispermities, vitus morphotypes). the wapiti assemblage at the pipestone creek mouth paleofloral site has a lower diversity assemblage containing well-preserved fossils of an angiosperm tree (c.f. menispermities morphotype) and at least one large gingko taxon. at the beaverlodge river paleofloral site, the wapiti assemblage is dominated by the conifers metasequoia and parataxodium and contains well-presented fossils of both terrestrial and aquatic angiosperms (c.f. menispermities, vitis and cercidiphyllum morphotypes). the dunvegan paleofloral assemblage, known as the mccoy leaf site, was collected in 2016 by staff at the philip j. currie dinosaur museum. despite a small sample of 20 specimens, the assemblage is surprisingly diverse, containing at least five morphotypes. the most common leaves were palmately lobed, similar to the sassafras morphotype. other leaves are similar to the morphotypes described as 122, 143 and 144 by ash et al. (1999). interestingly, the mccoy leaf site is entirely made up of angiosperms, lacking the conifer fossils so common in later cretaceous forests. while the sample size is still relatively small, these new paleofloral sites begin to create an interesting narrative about the development of forests in the late cretaceous of northern alberta. the plant fossil record of the middle cretaceous albian period in alberta has been well documented. kalyniuk et al. (2023) described the paleoflora from the albian grande cache formation, and the stomach contents of the coeval nodosaur borealopelta markmitchelli from the fort mcmurray area was described by brown et al. (2020). these forests appear to have been dominated by seed ferns, horsetails, and cycads, with very few angiosperms. some 40 million years later when the wapiti formation was deposited, the forests were fundamentally different, dominated by metasequoia and abundant angiosperms. although the sample size is small, the mccoy leaf site assemblage hints that the replacement of seed ferns and cycads may have occurred relatively rapidly as early as the cenomanian, rather than as a gradual replacement across the intervening turonian, coniacian and santonin periods. more cenomanian palaeofloras will be needed to support this hypothesis. both vegetation type and forest structure greatly influence the type of animals these late cretaceous forests could support. dinosaur body fossils from the albian and cenomanian deposits in northern alberta are dominated by ankylosaurids (burns and vavrek 2014; brown et al. 2020; arbour et al. 2020), a taxon that are almost entirely absent from the campanian wapiti formation. the same is largely true in the trace fossil (footprint) recvertebrate anatomy morphology palaeontology 11:1–41 10 ord. ankylosaurids such as borealopelta may have been fern specialists (brown et al., 2022), and the replacement of ferns by angiosperms may help to explain their demise. as we begin to understand the evolution of forests in northern alberta, the evolutionary and diversity of patterns of megaherbivores may become more apparent. literature cited arbour, v.m., d. larson, m. vavrek, l. buckley, and d. evans. 2020. an ankylosaurian dinosaur from the cenomanian dunvegan formation of northeastern british columbia, canada. fossil record 23:179–189. ash, a., b. ellis, l.j. hickey, k. johnson, p. wilf, and s. wing. 1999. manual of leaf architecture, smithsonian institution, washington, d.c., smithsonian institution, 65 pp. bell, p.r., f. fanti, p.j. currie, and v.m. arbour. 2014. a mummified duck-billed dinosaur with a soft-tissue cock’s comb. current biology 24:70–75. brinkman, d.b. 2003. a review of nonmarine turtles from the late cretaceous of alberta. canadian journal of earth sciences, 40: 557–571. brown, c.m., d.r. greenwood, j.e. kalyniuk, d.r. braman, d.m. henderson, c.l. greenwood, and j.f. basinger. 2020. dietary palaeoecology of an early cretaceous armoured dinosaur (ornithischia; nodosauridae) based on floral analysis of stomach contents. article 200305. royal society open science 7(6). burns, m.e., and m.j. vavrek. 2014. probable ankylosaur ossicles from the middle cenomanian dunvegan formation of northwestern alberta, canada. plos one 9(5):e96075. cook, t.d., m.v.h. wilson, and a.m. murray. 2008. a middle cenomanian euselachian assemblage from the dunvegan formation of northwestern alberta. canadian journal of earth sciences 45:1185–1197. enriquez, n.j., n.e. campione, m.a. white, f. fanti, r.l. sissons, c. sullivan, m.j. vavrek, and p.r. bell. 2022. the dinosaur tracks of tyrants aisle: an upper cretaceous ichnofauna from unit 4 of the wapiti formation (upper campanian), alberta, canada. plos one, 17(2), p.e0262824. fanti, f., and t. miyashita. 2009. a high latitude vertebrate fossil assemblage from the late cretaceous of west-central alberta, canada: evidence for dinosaur nesting and vertebrate latitudinal gradient. palaeogeography, palaeoclimatology, palaeoecology 275:37–53. fanti, f., p.r. bell, and r.l. sissons. 2013. a diverse, high-latitude ichnofauna from the late cretaceous wapiti formation, alberta, canada. cretaceous research 41:256–269. fanti, f., p.j. currie, and m.e. burns. 2015. taphonomy, age, and paleoecological implication of a new pachyrhinosaurus (dinosauria: ceratopsidae) bonebed from the upper cretaceous (campanian) wapiti formation of alberta, canada. canadian journal of earth sciences 52:250–260. fanti, f., p.r. bell, m. vavrek, d. larson, e. koppelhus, r.l. sissons, a. langone, n.e. campione, and c. sullivan. 2022. filling the bearpaw gap: evidence for palaeoenvironment-driven taxon distribution in a diverse, non-marine ecosystem from the late campanian of west-central alberta, canada. palaeogeography, palaeoclimatology, palaeoecology 592:110923. kalyniuk, j.e., c.k. west, d.r. greenwood, j.f. basinger, and c.m. brown. 2023. the albian vegetation of central alberta as a food source for the nodosaurid borealopelta markmitchelli. palaeogeography, palaeoclimatology, palaeoecology 611:111356. mccrea, r.t., m.g. lockley, and c.a. meyer. 2001. global distribution of purported ankylosaur track occurrences; pp. 413–454 in: k. carpenter (ed.), the armoured dinosaurs. indiana university press, bloomington. vavrek, m.j., a.m. murray, and p.r. bell. 2014. an early late cretaceous (cenomanian) sturgeon (acipenseriformes) from the dunvegan formation, northwestern alberta, canada. canadian journal of earth sciences 51:677–681. spicer, r.a. 2006. clamp. www.open.ac.uk./earth-research/spicer/clamp/clampset1.html6/3/2006. canadian society of vertebrate palaeontology 2023 abstracts 11 discovery of a new permian ichnofossil assemblage from les iles-de-la-madeleine louis-philippe bateman1, hans c.e. larsson1, jérôme dubé2, dirley cortés1,3,4, andré mueller1, and richard cloutier2 1redpath museum, biology department, mcgill university, montreal, qc ,h3a 0c4, canada; louis-philippe.bateman@ mail.mcgill.ca; dirley.cortes@mail.mcgill.ca; andre.mueller@mail.mcgill.ca; hans.ce.larsson@mcgill.ca 2université du québec à rimouski, rimouski, qc, canada; richard_cloutier@uqar.ca; jerome_dube@uqar.ca 3smithsonian tropical research institute, balboa-ancón 0843–03092, panamá, panamá 4centro de investigaciones paleontológicas, km. 5.2 vía santa sofía, villa de leyva, colombia over the past two decades, locals, tourists, and geologists have found well-preserved early permian ichnofossils in the cap-aux-meules formation of les iles-de-la-madeleine, québec. to follow up on these discoveries, fieldwork was conducted in october 2022. this led to the discovery of several in situ and ex situ tetrapod trackways preserved mainly on sandstone horizons representing at least eight distinct ichnofossil morphotypes and some other unidentifiable traces, possibly produced by invertebrates. all vertebrate trackways are from quadrupedal animals and footprint lengths range from 2 to 6 cm. the trackways are preserved at various depths and taphonomic levels, which may suggest multiple walking events of several individuals in one and/or several levels. a few samples preserve footprints displacing the sediment outwards in anterior portions of the footprints which may correspond to events of higher speeds or made over substrate of varied inclination. others have characteristic downward tilted footbeds that we interpret as displacements during the end of the step cycle in wet but not saturated sands. the relatively similar footprint sizes suggest the tracks were produced by individuals of roughly similar body sizes. the tetrapod morphotypes preliminarily identified include potentially relatively well-known ichnotaxa such as dromopus, chelichnus, laoporus, dicynodontipus, and ichniotherium. preliminary comparisons with other ichnofossil assemblages from fossil collections in eastern canada, the united states, and europe suggest that les iles-de-la-madeleine had a typical euramerican ichnofauna. the age of the cap-aux-meules formation remains to be determined, but based on previous research, and the potential presence of dromopus, we suggest it to be equivalent to the dromopus biochron, which is early permian in age. the depositional environment of the site is still unresolved due to the complex maritimes basin history. specifically, the lack of bioturbation, the presence of the taphotaxon chelichnus, and the presence of large scale cross-bedding suggests that the site was deposited in an aeolian, sand dune environment overall referrable to the chelichnus ichnofacies. however, some ichnofossils show evidence of animals sinking into a presumably humid substrate, which would suggest a wetter depositional environment. for this reason, we suggest that the depositional environment may have been variable through time. future expeditions focused on the geology of the area will allow us to better understand the depositional paleoenvironments of the cap-aux-meules formation and its concordant units. altogether, this new ichnofossil site sheds new light on early permian ecosystems in the maritimes basin. these ichnofossils are also the first tetrapod fossils from quebec that date from before the quaternary glaciations. they therefore showcase the potential of les iles-de-la-madeleine for becoming a fossil hotspot in the province. ties were built with the municipal government during our visit, and we hope to set up a collaborative inter-institutional exhibit displaying these fossils on the islands in the near future to help support the education, culture, and science of the region. vertebrate anatomy morphology palaeontology 11:1–41 12 revisiting caudal vertebral fusion in mosasaurs (squamata: mosasauridae) using paleohistology: functional implications michael e. burns1, jun ebersole2, and sahara gonzalez3 1department of biology, jacksonville state university, jacksonville, al, 36265, usa; mburns3@jsu.edu 2mcwane science center, birmingham, al, 35203, usa; jebersole@mcwane.org 3lincoln memorial university college of veterinary medicine, harrogate, tn, 37752, usa; xsahara7@hotmail.com mosasaurs were large-bodied predatory marine squamates, exhibiting a hypocercal caudal morphology rare among extinct and extant vertebrates. secondary caudal functions, in addition to locomotion, have been ascribed to this anatomy as it pertains to mosasaurs. a high incidence of vertebral fusion has also been noted in their caudal regions since the 1870s. little research has investigated the etiology of these abnormalities, although most diagnoses have been based on gross anatomy. those that have examined bone microstructure have suggested etiologies such as avascular necrosis and healed injury, albeit on those specimens with clear gross signs of injury/pathology. alabama is rich in cretaceous marine fossils, with at least 1,300 individual specimens collected to date. in this study, we test three hypotheses to explain the occurrence of caudal vertebral fusion: normal development, pathology (e.g., infectious spondylitis), or healed injury. three specimens, collected from the upper cretaceous mooreville chalk formation, were used for paleohistological analysis. to perform this analysis, they were molded and cast, stabilized by resin impregnation, and petrographically on frosted plexiglass slides. externally, these specimens exhibit no indication of macroscopic abnormalities or healed injury. our analysis indicates incomplete in vivo fusion in two of the specimens; however, an unfused specimen shows trabecular bone in the medullary regions of the vertebrae. towards the cortex of the anterior and posterior margins, the bone tissue becomes denser, histology typical for normal vertebral development. a third specimen shows complete fusion. trabecular bone density is constant, and no evidence of woven bone (indicative of injury or a pathology) can be observed. histological evidence thus supports that this is indicative of normal bone development, and shares similarities with normal pygostyle development in birds; however, we cannot rule out remodeling as having erased some record of healed lesion or fracture. future work should expand the histological sample size available for mosasaur vertebrae, regardless of their gross anatomy. first pleistocene tetraodontid fish (teleostei, tetraodontiformes) from tanegashima island, japan mori chida1, and yoshitaka yabumoto2 1department of life and environmental engineering, university of kitakyushu, japan; gozdmori@gmail.com 2kitakyushu museum of natural history and human history; yabumoto@kmnh.jp tanegashima island is located in southwest japan and belongs to the kagoshima prefecture. many fossil specimens were excavated in 1988 and 1989 from the marine deposits of the pleistocene masuda formation of katanoyama in the northern part of the island. these fossils were named the ‘katanoyama fossil assemblage’ and contain various groups including plants, bivalves, crustaceans, amphibians, mammals, and a lot of fishes. the approximate age of canadian society of vertebrate palaeontology 2023 abstracts 13 the deposits is 1.3 ma. currently, at least 7 orders, and 13 families with 18 species of fishes have been recognized, including clupeiforms, anguilliforms, osmeriforms, beloniforms, mugiliforms, perciforms, and pleuronectiforms. however, only two species have been formally named, the clupeiform clupanodon tanegashimaensis (saheki, 1929) and the perciform percichthys chibei saheki, 1929. most of the fish specimens are now housed in the kitakyushu museum of natural history and human history (kmnh). in this study, we report on specimens that were rediscovered in the collections of the kmnh as the first well-preserved pleistocene tetraodontids. tetraodontidae is a family of pufferfish that includes 28 extant genera with more than 180 species that live in marine, brackish, and freshwater environments of the temperate to tropical zones. most tetraodontids have a unique neurotoxin called tetrodotoxin in their skin and organs, as well as in the muscles of some species. diagnostic features of this group include having four beak-like fused teeth, lacking pelvic girdles, ribs, and intermuscular bones, and possessing 7-18 dorsal and anal fin rays with no fin spines. the fossil record of tetraodontids spans the eocene of italy, oligocene of russia, miocene of ukraine, and pliocene of the united states, and some fragmentary specimens have also been found in oligocene to miocene deposits of the middle east. the specimens found in tanegashima consist of five individuals. all of them are nearly complete except for one that lacks the anterior part of the skull. two of the specimens lack small spines called prickles on the body, whereas the other three possess prickles on the anterior part of the body. based on the overall osteology, presence/ absence of prickles, and the number of fin rays and vertebrae, the specimens appear similar to the extant genus takifugu. however, the specimens also possess some characters that differ from takifugu, such as the morphology of the bones of the caudal skeleton. thus, these specimens expand our knowledge of the pufferfish that lived in southwestern japan and the northwest pacific ocean a million years ago. comparison of the efficacy of 2d and 3d tooth shape morphometrics for predicting the diets of carnivorous mammals brigid e. christison1 and danielle fraser2 1canadian museum for human rights, winnipeg, mb, r3c 0l5, canada; brigid.christison@outlook.com 2canadian museum of nature natural heritage campus, gatineau, qc, j9j 3n7, canada; dfraser@nature.ca digital scanning and 3d models have revolutionized the study of morphological evolution. in some fields, 3d analyses have nearly supplanted more traditional studies based on 2d linear measurements. digital scanning is more costly than 2d methods, yet few studies have compared the efficacy of 3d to 2d methods in the analysis of surface morphology. the objective of the present study is therefore to make direct comparisons of 3d and 2d methods for inferring diet based on tooth shape. tooth shape reflects the average diets of extant mammals and has been applied to close relatives for the purpose of inferring the diets of extinct species. here, we compare the efficacy of dietary inference among extant carnivorans between 3d metrics of dental shape complexity (orientation patch count and relief index), with several 2d metrics of quantifying surface shape. we compared rates of correct dietary classification using linear discriminant analyses and tests for statistically significant differences among dietary groups. the sample size and selection of included species also influences the separation of species by diet. though higher sample sizes in this study correspond with lower percent correct classification, they are likely more accurate in terms of determining the true efficacy of the methods. we found that 2d and 3d metrics combined yielded the highest rates of correct classification, but that 2d metrics relating to the form of the carnassial tooth (lower first molar). we therefore suggest that 2d metrics are a valid means of inferring carnivorous mammal diet in the fossil record. vertebrate anatomy morphology palaeontology 11:1–41 14 immature daspletosaurus (tyrannosauridae, tyrannosaurinae) material from the dinosaur park formation of alberta, canada colton c. coppock1, mark j. powers1, jared t. voris2, and philip j. currie1 1department of biological sciences, university of alberta, b edmonton, alberta, t6g 2r3, canada 2 department of geoscience, university of calgary, calgary, alberta, t2n 1n4, canada understanding the extent to which ontogeny altered tyrannosaurid cranial morphology remains integral when referring tyrannosaurid specimens at varying life stages to a taxon. yet, elements diagnostic to a tyrannosaurid species that belong to an immature tyrannosaurid specimen remain exceedingly elusive. over the last century the university of alberta has collected two isolated immature cranial elements referable to daspletosaurus from the dinosaur park formation of dinosaur provincial park, alberta: a pathologic jugal (ualvp 61561) and a lacrimal (ualvp 47955). to assess the diagnosability of these elements, they were compared to additional tyrannosaurid material from the dinosaur park formation. this provided an opportunity to examine size-independent discrete characters in tyrannosaurid crania. the results of this study suggest that many jugal and lacrimal discrete characteristics observed in daspletosaurus are constrained throughout ontogeny despite disparity in size. ontogenetically invariant characters present on the daspletosaurus jugal include, but are not limited to, the presence of a postorbital fossa and an anteroposteriorly broad medial flange along the postorbital contact shelf. the most axiomatic invariant lacrimal characters include a restricted pneumatic recess opening that does not approach the cornified region of the lacrimal horn and a lateral surface of the ventral ramus that is broadly confluent with the jugal ala. the presence of invariant characters on two cranial elements allows specimens of the tyrannosaurine daspletosaurus and the albertosaurine gorgosaurus to be confidently distinguished regardless of ontogenetic stage. a new pliosaur from the early cretaceous paja formation of colombia: insights into the diversification of brachaucheniinae dirley cortés1,2,3, mary luz parra-ruge3, alexandre demers-potvin1, and hans c.e. larsson1 1redpath museum, biology department, mcgill university, montreal, qc, h3a 0c4, canada; dirley.cortes@mail.mcgill.ca; hans.ce.larsson@mcgill.ca; alexandre.demers-potvin@mail.mcgill.ca 2smithsonian tropical research institute, balboa-ancón 0843–03092, panamá, panamá. 3centro de investigaciones paleontológicas, villa de leyva, boyaca, colombia; mlparra@centropaleo.com pliosaurid plesiosaurs are large-bodied, marine apex predators that lived throughout the jurassic and cretaceous. only brachaucheniine pliosaurs survived the end-jurassic extinction with this clade radiating during the early cretaceous. their radiation during this period is poorly documented with only a few known taxa. canadian society of vertebrate palaeontology 2023 abstracts 15 this study presents a new early cretaceous pliosaur from the paja formation of colombia. this new, exquisitely preserved pliosaur consists of a large complete skull about 1.2 m long with complete dentition. it features many autapomorphies, including a laterally constricted dentary and upper jaw near the orbits, similar to an odontocete whale, with a nearly tubular snout for almost half the skull length, and a hypertrophied frontal-parietal contact with rugose, striated ornamentation over the interorbital region, constructing a wide dorsal interorbital surface. these features are remarkable in comparison to morphological traits known in the other pliosaurs described from the formation. a phylogenetic analysis places the new pliosaur within brachaucheniinae, contributing to the taxonomic diversity of this clade. this new taxon is coeval, or nearly at the same horizon in the paja formation, with stenorhychosaurus, kronosaurus (=monquirasaurus), and sachicasaurus. the well-preserved nature of these taxa helps clarify phylogenetic hypotheses during the early cretaceous radiation of the clade. most notably, this radiation is characterized not only by high morphological disparity, but also a high upper range of body sizes for all plesiosauria. the high diversity of top predators in the paja formation is striking and differs from that of most other mesozoic marine ecosystems. the different skull shapes and tooth morphologies suggest niche partitioning among these taxa. this implies an equally complex apex predator ecosystem for the paja biota, despite the paucity of smaller vertebrate fauna. we present morphometric comparisons across the teeth of these paja brachaucheniines and hypothesize their feeding guilds within the known ecosystem. our work on this new pliosaur taxon provides new data on the paja’s ecosystem complexity and food web interactions and sheds light on the ecological roles of the brachaucheniines, the last surviving pliosaur top predators, during the late mesozoic before their imminent extinction. funding: the bess-neo program, nserc create 46283-2015, the smithsonian tropical research institute, the anders foundation, the 1923 fund, and gregory d. and jennifer walston johnson, the redpath museum’s delise alison award-2019, the sigma xi grant-in-aid-of-research (giar), canada-2019, and the quebec center for biodiversity science excellence award-2019, frqnt, canada. habitat heterogeneity and ape evolution in the early miocene of eastern africa susanne m. cote1, alan l. deino2, david l. fox3, john d. kingston4, rahab n. kinyanjui5, william e. lukens6, laura m. maclatchy4, kieran p. mcnulty7, daniel j. peppe8, james b. rossie9, and caroline a.e. strömberg10 1department of anthropology and archaeology, university of calgary, calgary, ab, t2n 1n4, canada; scote@ucalgary.ca 2berkeley geochronology center, berkeley, ca, 94709, usa; adeino@bgc.org 3department of earth & environmental sciences, university of minnesota, minneapolis, mn, 55455, usa; dlfox@umn.edu 4department of anthropology, university of michigan, ann arbor, mi, 48109, usa; jkingst@umich.edu; maclatch@umich.edu 5department of earth sciences, national museums of kenya, nairobi, 0100, kenya; rkinyanj@gmail.com 6department of geology & environmental science, james madison university, harrisonburg, va, 22807, usa; lukenswe@jmu.edu 7department of anthropology, university of minnesota, minneapolis, mn ,55455, usa; kmcnulty@umn.edu 8department of geosciences, baylor university, waco, tx, 76706, usa; daniel_peppe@baylor.edu 9department of anthropology, stony brook university, stony brook, ny, 11794, usa; james.rossie@stonybrook.edu 10department of biology, burke museum of natural history and culture, university of washington, seattle, wa, 98195, usa; caestrom@uw.edu vertebrate anatomy morphology palaeontology 11:1–41 16 research on eastern african catarrhine and hominoid evolution (reache) is a consortium of paleontologists and geologists that work together to study the early miocene (23–16 ma) in eastern africa. early miocene fossil localities in this region provide a critical window into early ape evolution, as this is the region in which the first clear hominoids occur. fundamentally, we seek to understand what kinds of environments early apes were living in, and how those environments shaped their morphological adaptations and ecology. apes today are largely confined to forested habitats, which is often assumed to represent the ancestral habitat for hominoids, but there is little data from the fossil record to support or refute this hypothesis. in two recently published papers (maclatchy et al. 2023; peppe et al. 2023), we provide paleoenvironmental reconstructions for early miocene fossil localities from across eastern africa, with a particularly detailed reconstruction at moroto, the oldest of the fossil sites (21 ma). our approach is multi-proxy, incorporating information from not only carbon isotopes in multiple paleosol-derived substrates (pedogenic carbonates, soil organic matter, and plant wax biomarkers) but also phytoliths, the silica remains of plant cells or cell walls, which can be diagnostic for different plant taxa. at moroto, we combined these data with revised dating, stable carbon and oxygen isotopes from mammalian enamel, and detailed reconstructions of the locomotor and dietary adaptations of the early large-bodied hominoid, morotopithecus (21 ma). our results demonstrate that the early miocene of eastern africa was characterized by heterogeneous environmental conditions. notably, we document that c4 grasses appear in africa more than 10 myr earlier than previously thought. these grasses are widespread in the region and can be locally abundant. they contribute to diverse habitats that range from forests to wooded grasslands, including the oldest grass-dominated habitats (roughly 30% c4 biomass or more) both in africa and globally. furthermore, multiple dietary and paleoecological proxies demonstrate that the oldest postcranially derived ape, morotopithecus, which shows clear specializations for othogrady combined with vertical climbing abilities, lived in a seasonal woodland habitat with a fragmented canopy and significant c4 grass cover and fed largely on leaves. in conclusion, this research demonstrates that early miocene apes were not confined to forested habitats, but lived in heterogeneous environments that included open habitats with sparse tree cover (wooded grasslands). postcranial adaptations for suspensory locomotion and acrobatic climbing may not have evolved to help apes feed on fruit in a continuous canopy, but to forage for leaves in a habitat characterized by large gaps between trees. literature cited maclatchy, l.m., s.m. cote, a.l. deino, r.m. kityo, a.t. mugume, j.b. rossie, w.j.sanders, m.n. cosman, s.g. driese, d.l. fox, a.j. freeman, r.j.w. jansma, k.e.h. jenkins, r.n. kinyanjui, w.e. lukens, k.p. mcnulty, a. novello, d.j. peppe, c.a.e. strömberg, k.t. uno, a.j. winkler, and j.d. kingston. 2023. the evolution of hominoid locomotor versatility: evidence from moroto, a 21 ma site in uganda. science 380:eabq2935. peppe, d.j., s.m. cote, a.l. deino, d.l. fox, j.d. kingston, r.n. kinyanjui, w.e. lukens, l.m. maclatchy, a. novello, c.a.e. strömberg, s.g. driese, n.d. garrett, k.r. hillis, b.f. jacobs, k.e.h. jenkins, r.m. kityo, t. lehmann, f.k. manthi, e.n. mbua, l.a. michel, e.r. miller, a.t. mugume, s.n. muteti, i.o. nengo, k.o. oginga, s.r. phelps, p. polissar, j.b. rossie, n.j. stevens, k.t. uno, and k.p. mcnulty. 2023. oldest evidence of significant c4 grasses and habitat heterogeneity in eastern africa. science 380:173–177. canadian society of vertebrate palaeontology 2023 abstracts 17 first definitive occurrence of centrosaurus apertus in saskatchewan reported from a multigeneric bonebed within the easternmost outcrop of the dinosaur park formation alexandre v. demers-potvin1, emily l. bamforth2 and hans c.e. larsson1 1redpath museum, mcgill university, montréal, qc, h3a 0c4, canada; alexandre.demers-potvin@mail.mcgill.ca; hans.ce.larsson@mcgill.ca 2philip j. currie museum, wembley, ab, t0h 3s0, canada; curator@dinomuseum.ca after more than a century of exploration, most of our knowledge on canadian late campanian communities comes from the fluvial-paralic deposits of the dinosaur park formation (dpf) in dinosaur provincial park (dpp), alberta. however, a growing list of localities from isolated dpf outcrops offers a glimpse into palaeocommunities that evolved closer to the western interior seaway, in approximate co-occurrence with the dpp biotas along an inland-coastal gradient. these include the muddy lake bonebed near unity, an associated ceratopsid skeleton near herschel, and a multigeneric bonebed located along lake diefenbaker in saskatchewan landing provincial park. over six field seasons from 2012 to 2018, field crews based in mcgill university collected fossils from the latter locality as part of an annual palaeontology field course. the specimens were subsequently prepared and studied at the redpath museum, montréal, on loan from the royal saskatchewan museum. a palaeoecological analysis of this ancient coastal ecosystem based on the palynomorphs and vertebrate microfossils collected between 2012 and 2015 has now lain a foundation for the current study of its macrofossil assemblage. over a total of ~50 m2 uncovered at the lake diefenbaker bonebed, around 300 vertebrate macroand microfossils found in the same bone layer were excavated (not including surface-collected microfossils). 73 of these macrofossils were identified as ceratopsid, one of which consists in an incomplete right lateral parietal bar that bears the hooked p1 and p2 parietal processes diagnostic of centrosaurus apertus. other ceratopsid elements are assigned to cf. centrosaurus due to anatomical similarities with albertan specimens combined with an absence of diagnostic characters. we refrain from classifying the lake diefenbaker bonebed as a centrosaurusdominated catastrophic death assemblage because ceratopsid remains represent a minority of its identifiable fossils. nonetheless, the description of the macrofauna from the most extensive dinosaur bonebed known from saskatchewan to date increases the known diversity of the community that evolved in this coastal outpost of the dpf and represents a major contribution to the palaeontological heritage of this province. the aforementioned parietal bar is shown to fall well within the range of variation in parietal process angulation observed in centrosaurus apertus specimens from alberta, which precludes its assignment to a new centrosaurus species. therefore, it constitutes the first diagnostic morphological evidence for the presence of c. apertus in saskatchewan. the unequivocal presence of this ceratopsid on the eastern coast of laramidia suggests that the lake diefenbaker bonebed is closer in age to the lower dpf in dpp, which is at odds with a previous correlation to the upper dpf in dpp based on the palynoflora. considering evidence of temporal turnover among centrosaurine species within dpp, as well as highly documented shifts in the geographic distributions of extant floral assemblages in response to environmental change, the presence of centrosaurus in the lake diefenbaker bonebed is proposed to be a more reliable indicator of relative age for this locality’s campanian deposits than its palynofloral composition. this contribution demonstrates how evidence from multiple localities in the dpf along a spatial gradient, beyond the temporal gradient available within dpp alone, completes the picture of this extensively studied metacommunity at a regional scale. vertebrate anatomy morphology palaeontology 11:1–41 18 disparate life histories contributed to the palaeocene rise of eutheria gregory f. funston1,2, sofia holpin2, sarah l. shelley2, thomas e. williamson3, and stephen l. brusatte2 1royal ontario museum, toronto, on, canada; greg.funston@rom.on.ca 2school of geosciences, university of edinburgh, edinburgh, uk; sofia.holpin@ed.ac.uk, sarah.shelley@ed.ac.uk, stephen.brusatte@ed.ac.uk 3new mexico museum of natural history and science, albuquerque, nm, usa; thomas.williamson@state.nm.us the early palaeocene (66.0–61.6 mya) witnessed the establishment of mammal-dominated terrestrial ecosystems after the extinction of the non-avian dinosaurs. understanding the mammals that formed these communities is crucial not only for disentangling the origin of living mammal clades, but also the dynamics that shaped these first antecedents of modern ecosystems. the potential role of life history as a driving factor in the composition of early mammalian ecosystems has long been appreciated but has historically been difficult to evaluate. a central focus thus far has been on differences in reproductive strategy between major mammal clades, particularly multituberculates, metatherians, and eutherians. however, virtually no work has considered whether variable reproductive strategies existed within these clades, and what effect it may have had on ecosystem dynamics. recent advances combining palaeohistology with geochemistry have now opened a new window into the life histories of extinct mammals, revealing a highly precocial (rapidly-developing) lifestyle in the eutherian pantodont pantolambda, but it is unclear whether this is representative of eutherians more broadly. here we present preliminary results for another eutherian, the phenacodontid tetraclaenodon, which is represented by several skeletons with deciduous dentition. surprisingly, consilient evidence from both cementochronology and postcranial osteohistology indicate a much slower life history in tetraclaenodon, at virtually the opposite end of the eutherian spectrum from pantolambda, despite only minor differences in body mass. after a relatively short gestation period (~2 months), tetraclaenodon retained the slow-growing deciduous teeth for as long as four years. the oldest individual in our sample grew exceptionally slowly towards the end of its life, which spanned at least 8–9 years. the intersection of gestation period and body size (10–15 kg) in tetraclaenodon is similar to small-bodied carnivorans like the coyote (canis latrans), caracal (caracal caracal), and african civet (civettictis civetta). however, these extant species vary significantly in the duration of suckling (1.5–4 months), so determination of the closest modern analogue for tetraclaenodon awaits trace element geochemical work in progress. nonetheless, these results indicate that eutherian life histories were already diverse in the early palaeocene, and raise doubts that a more precocial ‘placental’-style life history is responsible for the greater proliferation of eutherians than other mammal clades during this interval. mosasaur feeding ecology of the bearpaw formation, alberta, canada: the final chapter femke m. holwerda royal tyrrell museum of palaeontology, drumheller, ab, t0j 0y0, canada; femke.holwerda@gov.ab.ca the campanian bearpaw formation (~80–75 ma) deposits of southern alberta host a score of large marine reptiles: mosasaurs (typically mosasaurus missouriensis, tylosaurus proriger, prognathodon overtoni, and canadian society of vertebrate palaeontology 2023 abstracts 19 plioplatecarpus primaevus), elasmosaurs, and turtles. other vertebrate inhabitants were sharks, sawfish, other predatory fish like enchodus, and invertebrates such as lobsters, ammonites, and bivalves. previously, microwear, energy dispersive x-ray (edx) analysis, and isotope pilot studies were used to demonstrate niche partitioning amongst the large marine predators. however, δ18o range (indicative of salinity levels and water temperature), and 87sr/86sr isotopes (indicative of migratory patterns) suggest that habitat partitioning is the main key to reducing competition for these large marine predators. prognathodon shows the largest range in both oxygen and strontium isotopes, indicating migration, followed by plioplatecarpus. platecarpines have been suggested in prior studies to migrate between fresh and saltwater bodies. the δ18o range of marine turtles is equally wide. interestingly, mosasaurus shows a narrow range, and tylosaurus shows an equally narrow, but decidedly offset range of values from all other mosasaurs. the latter overlaps with ammonites, showing a possible preference for foraging in the upper water column. all lines of evidence together suggest that some mosasaurs had preferred foraging depths, and that others, like prognathodon, foraged between offshore and nearshore habitats. it is interesting to note, however, that oxygen isotope studies across various localities of the western interior seaway tend to find slightly offset values. this could reflect local water body differences, i.e., small differences in salinity, runoff, and temperatures. comparative dental microwear analyses of north american ursids to infer the dietary palaeoecology of extinct pleistocene short-faced bears from the yukon howard m. huynh1, prieyankaa nirmalan2, and danielle fraser1,3,4 1beaty centre for species discovery, canadian museum of nature, po box 3443 stn “d”, ottawa, on k1p 6p4, canada; hhuynh@nature.ca, dfraser@nature.ca 2department of biology, university of ottawa, ottawa, on, k1n 9a7, canada 3department of biology, carleton university, ottawa, on, k1s 5b6, canada ⁴department of earth sciences, carleton university, ottawa, on, k1s 5b6, canada the extinction of the majority of north america’s mammal megafauna occurred at the end of the pleistocene approximately 11.7 ka. short-faced bears (arctodus simus), the largest carnivoran members of the mammalian megafauna at the end of the pleistocene, were amongst those that became extinct. however, the ecological characteristics (e.g., diet, behavior, life history) that may have increased extinction risk for a. simus, relative to the other extant north american bears, remain unresolved. dietary specialization is particularly known to enhance extinction risk among mammals. thus we aim to reconstruct the diet of a. simus from the yukon, canada using dental microwear analysis and compare it to extant sympatric north american ursids. lower molars (m1 and m2) were molded, cast, and imaged using scanning electron microscopy from vouchers of a. simus, brown bear (ursus arctos), black bear (ursus americanus), and polar bear (u. maritimus). the number of pits and scratches were counted and statistically compared. analyses of variance showed significant differences in mean numbers of pits (df = 3, f = 7.343, p < 0.05) and scratches (df = 3, f = 6.182, p < 0.05) among all species. despite previous isotopic characterization of a. simus as a highly specialized carnivore, we show that this species may have had a more varied diet consisting of meat and hard foods such as leaves, seeds, and fruit similar to u. arctos. hence, we surmise that a. simus may not have been a dietary specialist but rather a generalist omnivore, which means that diet may not have been an inherent extinction risk factor that contributed to their extinction. vertebrate anatomy morphology palaeontology 11:1–41 20 size reduction in beringian equus throughout the late pleistocene leading up to their extinction zoe landry1,2, clément p. bataille1,3, and danielle fraser2,4,5,6 1department of earth sciences, university of ottawa, ottawa, on, k1n 6n5, canada; zland032@uottawa.ca 2beaty centre for species discovery, canadian museum of nature, ottawa, on, k1p 6p4, canada; dfraser@nature.ca 3department of biology, university of ottawa, ottawa, on, k1n 9a7, canada; cbataill@uottawa.ca ⁴department of earth sciences, carleton university, ottawa, on, k1s 5b6, canada ⁵department of biology, carleton university, ottawa, on, k1s 5b6, canada ⁶paleobiology smithsonian national museum of natural history, washington, dc, 20560, usa body mass changes in response to global climatic shifts are well-documented phenomena in mammals; large mammals tend to exhibit rapid decreases in body mass as temperatures rise, consistent with bergmann’s rule. body mass estimates from limb bones suggest that beringian horses (equus ferus) from alaska underwent a considerable decline in body mass (~15%) over approximately 25 ka leading up to their extinction near the end– pleistocene. here, we investigate whether the same trend can be observed in the teeth of beringian horses from the yukon, as, much like limb bones, mammalian teeth are considered good predictors of body mass. we took measurements from 3rd and 4th premolars of beringian equus lambei and equus sp. specimens from the collections of the canadian museum of nature to generate body mass estimates, and we subsequently radiocarbon dated the specimens at the a.e. lalonde ams laboratory. preliminary analyses show that yukon beringian horses underwent a drastic reduction in body mass (~60%) from >44–4 ka. we suggest that, consistent with previous work, the decrease in body mass was likely driven primarily by either: 1) changes in climatic and/or vegetation regimes, or 2) by species-specific differences in body mass and species turnover, although we acknowledge that further research is required in order to determine which of these two possible explanations is better supported. these early results lend support for bergmann’s rule in perissodactyls and could help to inform future research regarding extinction drivers of northern north american pleistocene megafauna. sense and sensibility: estimating the hearing capability of otophysan fish and implications for their fossil relatives juan liu department of integrative biology, university of california, berkeley, berkeley, ca 94720, usa; and university of california museum of paleontology, berkeley, ca 94720, usa) sensory biology is an area of vertebrate evolution and paleontology that has remained relatively inaccessible because of the rarity of preservation. recent advances in imaging and computational modelling have permitted a renewed research program focusing on sensory system structure and function. here i introduce a new framework for studying auditory system variation and adaptation in fishes using dynamic finite element analysis (dfea). the model organism utilized in this study was zebrafish (danio rerio) which allowed for creation of a baseline and 3d geometric models of weberian ossicles of a sample of otophysans were constructed from high-resolution x-ray computed tomographic data. the 3d models were subjected to modal and harmonic dynamic finite element analyses to evaluate how ossicle chains respond to a range of auditory frequencies. results indicate that the simucanadian society of vertebrate palaeontology 2023 abstracts 21 lated resonance frequency in the dfea models matches hearing frequencies obtained from behavioral and electrophysiological audiogram data. furthermore, resonance frequency exhibits a negative covariation with ossicle size but appears to be isometric after size correction. these findings suggest that dfea demonstrates potential to permit improved estimation and reconstruction of the hearing capability of extinct otophysan fish taxa. this approach forms a basis for future applications to analyzing hearing ossicles in other vertebrates in non-aquatic habitats such as terrestrial, subterranean, and aerial environments. the timing and ecological evolution of modern ant lineages elyssa loewen1,4, caelan libke1, christine sosiak2, phillip barden2, christopher somers1, and ryan c. mckellar1,3,4 1biology department, university of regina, regina, sk, s4s 0a2, canada; elyssa.loewen18@gmail.com; caelan.libke@ gmail.com; chris.somers@uregina.ca 2federated department of biological sciences, new jersey institute of technology, rutgers-newark university, newark, new jersey, 07102, usa; ces43@njit.edu, barden@njit.edu 3department of ecology & evolutionary biology, university of kansas, lawrence, kansas, 66045, usa ⁴royal saskatchewan museum, regina, sk, s4p 2v7, canada; ryan.mckellar@gov.sk.ca ants are an integral and ubiquitous component of modern ecosystems where they play an outsized role as ecosystem engineers due their significant phylogenetic and ecological diversity, and sheer abundance. our understanding of ant evolution and how they came to dominate modern ecosystems is severely limited by a 17-million-year gap in the ant fossil record spanning the maastrichtian to the early eocene. during this gap, which buffers the end-cretaceous (k-pg) mass extinction (66 ma), all stem ant lineages appear to go extinct; when the fossil record resumes in the eocene, only crown lineages (i.e., lineages that diverged from the common ancestor of modern ants) remain. here, we report two crown ants (formicidae) from a diverse late cretaceous (67.04 ± 0.16 ma) amber assemblage in the big muddy badlands of saskatchewan that fills this critical faunal gap. the unexpectedly high abundance of crown ants in big muddy amber suggests that the stem-to-crown ant faunal turnover occurred, or at least was underway, before the k-pg extinction. these two ant fossils represent only the second record of aneuretinae from cretaceous amber, and the oldest record for the genus tetraponera (pseudomyrmecinae), pushing their estimated age and split from other pseudomyrmecinae genera back into the cretaceous. both ants also have relictual modern relatives: aneuretinae is restricted to a single species in sri lanka, aneuretus simoni, and the genus tetraponera is restricted to the palaeotropics and australia. we reconstructed the palaeoecology of the big muddy ants and compared them to the ecological occupations of their modern relatives using a predicted random forest model. we determined that the ecology of these now relictual lineages has shifted since the maastrichtian when these ants lived in the northern hemisphere. we recovered the big muddy aneuretinae as a carton-nesting arboreal omnivore (out-of-bag (oob) error 21.4%), in contrast to modern aneuretus simoni, which is a leaf-litter omnivore. the fossil tetraponera species appears to be a leaf-litter nesting epigaeic omnivore (oob error 16.25%) in contrast to modern tetraponera species, which are lignicolous arboreal phytophages. these results indicate that, in addition to occupying a larger geographic distribution in the cretaceous, both ant lineages occupied a wider range of ecological niches. it is likely that palaeoenvironmental and biotic changes in the late cretaceous and throughout the cenozoic impacted the evolution and ecological occupations of these ant lineages, resulting in their extirpation from large portions of their ancestral range. the faunal turnover of ecologically dominant ant groups may indicate significant changes within terrestrial environments and biotic communities one million years before the k-pg mass extinction. vertebrate anatomy morphology palaeontology 11:1–41 22 a petrified struggle for survival from the lower cretaceous deposits of china jordan c. mallon1,2, gang han3,4, aaron j. lussier5, xiao-chun wu1, robert mitchell6, and ling-ji li7 1beaty centre for species discovery and palaeobiology section, canadian museum of nature, ottawa, on, canada; jmallon@nature.ca; xcwu@nature.ca. 2department of earth sciences, carleton university, ottawa, on, canada 3hainan vocational university of science and technology, haikou city, hainan province, china; hg0805@126.com ⁴hainan tropical ocean university, sanya city, hainan province, china ⁵beaty centre for species discovery and mineralogy section, canadian museum of nature, ottawa, on, canada; alussier@nature.ca ⁶department of geography, university of calgary, calgary, ab, canada; robert.mitchell1@ucalgary.ca ⁷weihai ziguang shi yan school, weihai city, shandong province, china; lilingji@unisedu.com dinosaurs and mammals arose during the late triassic, and have coexisted for the last 230 million years (the former as birds, following the end-cretaceous mass extinction). mesozoic dinosaurs are commonly depicted as having overshadowed the contemporaneous mammal fauna, and several examples of fossil gut contents reveal that small mammals were regularly incorporated into the diets of the larger dinosaurs. it was not until the cenozoic that mammals eventually outgrew and regularly preyed upon the available avifauna. however, the interaction of dinosaurs and mammals during the mesozoic was not always so unilateral. in 2005, a fossil was described from the lower cretaceous lujiatun beds of china showing the opossum-sized mammal repenomamus robustus with gut contents consisting of the juvenile remains of the parrot-beaked dinosaur psittacosaurus cf. p. lujiatunensis. here, we report on a yet more impressive find from the same beds, showing these two species locked in mortal combat. the dinosaur is approximately three times larger than the mammal by body mass, estimated from standard limb scaling relationships. their skeletons are intimately intertwined, with the mammal gripping both the lower jaw and hindleg of the dinosaur as it bites into the dinosaur’s ribcage. we consider various hypotheses for this unique association, but conclude that the evidence on balance supports the interpretation that this fossil represents a predation attempt on the part of the mammal, suddenly entombed by a lahar-type volcanic debris flow, approximately 125 million years ago. insights and limitations in reconstructing the musculature and skeletal arrangement of the foot in tyrannosaurids and other non-avian theropod dinosaurs annie p. mcintosh1, corwin sullivan1, john acorn2, and philip j. currie1 1department of biological sciences, university of alberta, edmonton, ab, t6g 2e9, canada; apmcinto@ualberta.ca; corwin1@ualberta.ca; pjcurrie@ualberta.ca 2department of renewable resources, university of alberta, edmonton, ab, t6g 2e9, canada; jacorn@ualberta.ca canadian society of vertebrate palaeontology 2023 abstracts 23 the reconstruction of the skeleton and its associated musculature in fossil taxa depend on the ability to identify the locations of the tendinous muscle insertions and ligamentous bone-to-bone contacts on the fossilized skeletal elements. however, researchers have not agreed on the identifications of various rugose marks on the bones of the foot in tyrannosaurids and other non-avian theropods, resulting in inconsistent reconstructions of the foot, and specifically of the contact between the first and second metatarsals (tarsitano 1984; norell and makovicky 1997; carrano and hutchinson 2002; hattori 2016). at some point during the evolution of birds, the first digit (hallux) migrated distally along the second metatarsal from the ankle and became reversed to oppose the other digits (botelho et al. 2015). additionally, whereas the gastrocnemius muscle (m. gastrocnemius) inserts onto the tarsometatarsus in modern birds, it inserts onto the calcaneum in crocodilians and other tetrapods (reilly and blob 2003; klinkhamer et al. 2017). this indicates that a distal migration of the insertion of m. gastrocnemius occurred at some point on the evolutionary line to birds. ligaments and tendons, which attach bone to bone and to muscle, respectively, are structurally similar and both composed of collagen (zschäbitz 2005), and studies have found it difficult to accurately identify osteological correlates of these types of soft tissue insertions on bone and to distinguish between them (petermann and sander 2013; rothschild et al. 2016). therefore, any rugose marks present on the bones of the foot in fossil taxa could in principle represent either muscle attachments or contacts with other bones, and osteological evidence of these attachments may not be present at all in some taxa. in extant birds, m. gastrocnemius leaves proximally-positioned rugose patches on the medial and lateral edges of the posterior surface of the tarsometatarsus and the contact of the first metatarsal is easily identifiable by a distinct fossa located posterodistally on the tarsometatarsus (botelho et al. 2017). however, such clear osteological correlates are not always evident in fossil taxa, and undistorted, articulated specimens are relatively scarce. although reconstructions remain somewhat speculative and should be made cautiously, assumptions can be made based on the skeletal morphology and musculature of modern birds while recognizing the limitations of those assumptions. the morphology of the metatarsals is fairly consistent across late cretaceous north american tyrannosaurids, which have two posterior-facing rugose patches on the second metatarsal and one on the fourth metatarsal that is consistent with the proximal patch on the second metatarsal. based on the relative positions of the insertion of m. gastrocnemius and the contact of the hallux to the tarsometatarsus in modern birds, it is likely that the rugose patch on the fourth metatarsal and the proximal patch on the second metatarsal represent the insertions of m. gastrocnemius, whereas the distal patch on the second metatarsal represents the contact with the first metatarsal. this indicates that the hallux was distally positioned on the second metatarsal in tyrannosaurids and was to some degree reversed to oppose the other digits, similar to the conditions seen in modern birds. the metatarsals of dromaeosaurids and troodontids, however, are relatively smooth and lack distinct rugose patches like those found in tyrannosaurids, and more research is needed to more accurately reconstruct their morphology. literature cited botelho, j.f., d. smith-parades, s. soto-acuña, j. mpodozis, v. palma, and a.o. vargas. 2015. skeletal plasticity in response to embryonic muscular activity underlies the development and evolution of the perching digit of birds. scientific reports 5:1–11. botelho, j.f., d. smith-parades, s. soto-acuña, d. núñez-león, v. palma, and a.o. vargas. 2017. greater growth of proximal metatarsals in bird embryos and the evolution of hallux position in the grasping foot. journal of experimental zoology part b: molecular and developmental evolution 338:106–118. carrano, m.t., and j.r. hutchinson. 2002. pelvic and hindlimb musculature of tyrannosaurus rex (dinosauria: theropoda). journal of morphology 253:207–228. hattori, s. 2016. evolution of the hallux in non-avian theropod dinosaurs. journal of vertebrate paleontology 36:e1116995. klinkhamer, a.d., d.r. wilhite, m.a. white, and s. wroe. 2017. digital dissection and three-dimensional interactive models of limb musculature in the australian estuarine crocodile (crocodylus porosus). plos one 12:e0175079. norell, m.a., and p.j. makovicky. 1997. important features of the dromaeosaur skeleton: information from a new specimen. american museum novitates 3215:1–28. vertebrate anatomy morphology palaeontology 11:1–41 24 petermann, h., and m. sander. 2013. histological evidence for muscle insertion in extant amniote femora: implications for muscle reconstruction in fossils. journal of anatomy 222:419–436. reilly, s.m., and r.w. blob. 2003. motor control of locomotor hindlimb posture in the american alligator (alligator mississippiensis). journal of experimental biology 206:4327–4340. rothschild, b.m., d.r. wilhite, d.s. mcleod, and h. ting. 2016. historical biology 28:842–848. tarsitano, s. 1983. stance and gait in theropod dinosaurs. acta palaeontologica polonica 28:251–264. zschäbitz, a. 2005. anatomie und verhalten von sehnen und bändern. der orthopäde 34:516–525. bioerosion trace fossils on triceratops bones from the latest cretaceous frenchman formation, southwestern saskatchewan, canada jack r. milligan1, emily l. bamforth1,2, luis a. buatois1, and m. gabriela mángano1 1department of geological sciences, university of saskatchewan, saskatoon, sk, s7n 5e2, canada; jrm451@mail.usask.ca; luis.buatois@usask.ca; gabriela.mangano@usask.ca 2philip j. currie dinosaur museum, wembley, ab, t0h 3s0, canada; curator@dinomuseum.ca bioerosion trace fossils are biogenic structures that record evidence of behaviour in hard substrates, including rocks, wood, shells, and bones. vertebrate fossils with associated osteic bioerosion structures have been well documented globally throughout the mesozoic and cenozoic (251.90–66.0 ma, 66.0–0.0 ma). invertebrate and vertebrate trace makers have been identified in many instances, offering unique insights into taphonomy and paleoecology. while non-avian dinosaurs are commonly the focus of these studies elsewhere in the world, documented cases of bioeroded dinosaur material are less common in canada. herein, we present several triceratops specimens that feature a suite of bioerosion trace fossils from the maastrichtian frenchman formation in southwestern saskatchewan. several cranial fragments from one associated individual, rskm p3336, display large, unbranching tunnel-like structures that penetrate through the bone. these structures appear to be ornamented with bioglyphs as scratches and/or engravings inscribed in negative relief on the inner wall of the borings. a rib from another individual, rskm p3127.1, displays several trace fossils, including a deep, rounded chamber with constructed walls, and several smaller borings that are present on the cortical bone surface. these skeletal fragments occur in massive mudstones with abundant organic material interpreted as paleosols. trace fossils on vertebrate bones in continental settings have been commonly attributed to insects, dermestid beetles, and termites being the most cited. this assumption is partly due to the size of the trace fossils, and observations of modern dermestids as capable of necrophagous and osteophageous behaviour. these bioerosion structures were likely created post-mortem since there is no evidence of bone regrowth around the borings. analyzing the mechanisms behind the creation of these structures on triceratops bones is important for understanding the depositional setting and corresponding taphonomic pathway of these specimens, and the hidden diversity of invertebrate decomposers in the late cretaceous. this study hopes to serve as a template for future studies on the taphonomy of bioeroded vertebrate fossils using ichnology and sedimentology, especially when body fossil evidence of the trace maker is absent. canadian society of vertebrate palaeontology 2023 abstracts 25 the head, heart, and fins of a jawless stem gnathostome tetsuto miyashita1, michael i. coates2, kristen tietjen3, pierre gueriau⁴, and philippe janvier⁵ 1palaeobiology section, canadian museum of nature, ottawa, on, canada; tmiyashita@nature.ca 2department of organismal biology and anatomy, university of chicago, chicago, il, usa 3biodiversity institute and the museum of natural history, university of kansas, lawrence, ks, usa ⁴institut photonique d’analyse non-destructive européen des matériaux anciens, université paris-saclay, gif-sur-yvette, france ⁵centre de recherche en paléontologie – paris, museum national d’histoire naturelle, paris, france a conventional sister group to jawed vertebrates, osteostracans anchor synapomorphies and symplesiomorphies of the clade. this canonical view sets osteostracans in a mosaic of derived gnathostome traits (such as cellular bone) against the background of lamprey-like overall morphology (such as a blind nasohypophyseal canal). extensive studies of their perichondrally ossified endoskeletons have provided support for this interpretation. however, few ct scans have been undertaken for osteostracan internal anatomy. here we present preliminary results from a synchrotron x-ray tomography scan of a new specimen of norselaspis, and reveal surprisingly derived gnathostome traits in this osteostracan exemplar. contrary to the earlier interpretations, the vestibular sinus superiorsus is as tall in norselaspis as those in jawed vertebrates. the pericardial chamber is closed dorsally, which precludes the lamprey-like single midline cuvierian duct. there is no articular facet in the pectoral cavity, which suggests an entirely fleshy base of the pectoral fin. our three-dimensional model also enhances key findings from the previous reconstruction, including: configurations of the extraocular muscles and associated motor nerves, exogeneous infillings in the labyrinth, and brachial nerve arising as the most anterior spinal projections. these findings both refine and revise the stem-to-crown continuum of gnathostome characters. norselaspis has derived gnathostome conditions in the inner ear and circulatory system. however, we present evidence that endoskeletal joints emerge with the evolutionary origin of jaws; in this respect, norselapis remains resolutely plesiomorphic. interestingly, an apparent lack of the crown-like hypobranchial system in norselaspis implies its independent and divergent evolution in cyclostomes and gnathostomes. a juvenile pachycephalosaur (dinosauria: ornithischia) skeleton from the upper maastrichtian frenchman formation of saskatchewan, canada bryan r.s. moore1,2, david c. evans3,4, michael j. ryan1,5, r. timothy patterson1, and jordan c. mallon1,5 1department of earth sciences, carleton university, ottawa, on, k1s 5b6, canada; bryan.moore@ucalgary.ca 2department of biological sciences, university of calgary, calgary, ab, t2n 1n4, canada 3department of natural history, royal ontario museum, toronto, on, m5s 2c6, canada ⁴department of ecology and evolutionary biology, university of toronto, toronto, on, m5s 3b2, canada 5beaty centre for species discovery and paleobiology section, canadian museum of nature, ottawa, on, k1p 6p4, canada vertebrate anatomy morphology palaeontology 11:1–41 26 pachycephalosaurs are small (~2–6 m in length), bipedal, ornithischian dinosaurs that lived during the late cretaceous in asia and north america. they are best known for the characteristic fusion of their frontal and parietal bones into a thickened skull dome. these domes are their most commonly preserved element, in part because the less robust elements of their postcrania are more easily lost to post-mortem taphonomic processes. as a result, most inferences about pachycephalosaur growth, anatomy, and phylogenetics are based primarily on skull morphology. in this study we describe a small, partial pachycephalosaur postcranium (cmn 22039) from the uppermost maastrichtian frenchman formation of saskatchewan. the specimen was discovered by dale russell in 1973 at the base of a 6.7 m thick claystone unit, approximately 14 m below the ferris no. 1 coal seam (which approximates the k-pg boundary in this area). preserved elements include portions of the dorsal, sacral, and caudal vertebrae, assorted ribs, the complete pelvic girdle, and portions of the hind limb. the specimen was originally assigned to thescelosaurus, but was subsequently recognized as a pachycephalosaur based on several diagnostic characters, including the presence of a prominent flange projecting medially from the dorsal margin of the ilium, a double ridge-and-groove articulation of the preand post-zygapophyses of the dorsal vertebral arches, and an extremely reduced pubis that is nearly excluded from the acetabulum. osteohistological analysis of the tibia and fibula reveals an immature woven bone texture which lacks any lines of arrested growth or secondary remodeling. this, together, with the unfused neurocentral sutures of the vertebrae and the small size of the specimen (femur length = 84.5 mm), attest to the juvenile status of the individual. a cladistic parsimony analysis including cmn 22039 recovered it in a basal position in pachycephalosauridae, likely due to its lack of skull characters and its inferred juvenile status. based on its stratigraphic age, geographic location, size, and postcranial character states, we hypothesize that cmn 22039 represents a specimen of sphaerotholus buchholtzae and may be the first postcranial skeleton known for this genus. other possible taxonomic identities for cmn 22039 (alaskacephale gongloffi, pachycephalosaurus wyomingensis, and stygimoloch spinifer) either do not share diagnostic overlapping material with the specimen, or possess conflicting postcranial character states, and cannot be compared on this basis. cmn 22039 demonstrates that diagnostic pachycephalosaur characters are present in the postcranial skeleton even at the earliest stages of ontogeny, probably before the development of the characteristic skull dome. our study highlights the importance of evaluating the postcranial skeleton during taxonomic identification and shows that pachycephalosaur remains can be recognized at a young age even without cranial material. a multivariate comparison of the vertebrate faunas of the horseshoe canyon and wapiti formations of alberta, canada with implications for vertebrate biogeography nathaniel e.d. morley1, lindsey r. leighton1, eva b. koppelhus2, and philip j. currie1 1department of earth and atmospheric sciences, university of alberta, edmonton, ab, t6g 2e3, canada; nmorley@ ualberta.ca; lindseyrleighton@gmail.com 2department of biological sciences, university of alberta, edmonton, ab, t6g 2e9, canada; eva.koppelhus@ualberta. ca; pjcurrie@ualberta.ca the terrestrial biota of the latest campanian and early maastrichtian of alberta, canada is largely represented by two geological units: the horseshoe canyon formation and the wapiti formation. the strata of these formations were deposited in one geographically contiguous basin, with the former representing a coastal setting and canadian society of vertebrate palaeontology 2023 abstracts 27 the latter representing a somewhat more inland setting. the numerous well-sampled bonebeds from these formations provide an excellent opportunity to test whether a coastal-to-inland environmental gradient led to vertebrate endemism in the western interior basin, as has been previously hypothesised by qualitative studies. this study used ordination and multivariate statistical techniques on both occurrenceand abundance-based data to test for compositional heterogeneity among eight well-sampled (>100 identifiable specimens) bonebeds from the horseshoe canyon-wapiti system during a 2.7 ma time interval in the latest campanian. the results indicated that there is no significant compositional difference between the two formations, failing to support prior claims of vertebrate endemism resulting from a coastal-to-inland environmental gradient in the western interior basin. this study demonstrates the importance of assessing community-level data before drawing inferences on the community palaeoecology of a given system. identification of acanthomorph diversity in microvertebrate fossil sites alison m. murray1 and donald b. brinkman1,2 1department of biological sciences, university of alberta, edmonton, ab, t6g 2e9, canada; ammurray@ualberta.ca 2royal tyrrell museum of palaeontology, drumheller, ab, t0j 0y0, canada; don.brinkman@gov.ab.ca innumerable fossil fish specimens have been recovered from fossil microvertebrate sites – areas in which small, isolated elements of the skeleton from multiple individuals have been amassed. the accumulation of these skeletal elements is often the result of transportation by moving waters (e.g., rivers) for some distance prior to deposition, and thus they may be time averaged (i.e., accumulated over an unknown period of time). these accumulations provide an important window on the fauna that was present in a wider area during a broader period of time than that represented by individual articulated specimens. although microvertebrate sites provide important records of taxa, the disarticulated condition of the fossil elements can cause difficulties for taxonomical identification. this is particularly true for many fish. the most common fish element preserved in microfossil sites are vertebral centra; however, fish centra are notoriously difficult to identify at lower taxonomic levels, partly because of the vast numbers of living fish and lack of comparative collections. among one higher group, acanthomorpha, some progress is being made. arguably the most distinctive vertebral centrum among all fish is the first abdominal centrum of acanthomorpha. in acanthomorphs, the first centrum differs from that of all other groups of fishes in that it bears two distinct (separate left and right) facets for articulation with the exoccipitals, which are more or less dorsolateral to the articular facet for the basioccipital. this creates a unique tri-partite morphology of the first centrum in acanthomorphs. because there is only a single first vertebra in each fish, recognizing these first centra allows an accurate count of the minimum number of individual acanthomorph fishes that were present in the locality. these centra are also useful to identify the minimum number of different acanthomorph lineages present in the site, based on different morphologies of the first centrum. while different morphologies indicate the presence of different acanthomorph taxa, we are interested in gleaning more information from these elements by identifying the centra to lower taxonomic levels. this will allow us to gain an understanding of which acanthomorph lineages are present, rather than just numbers of lineages. to enable a better understanding of the acanthomorph taxonomic diversity in fossil sites, we are documenting the diversity of morphologies in extant taxa. ultimately, this research will lead to identifying specific features that are of phylogenetic value, and that will allow us to more narrowly identify which acanthomorphs are present in microvertebrate sites. vertebrate anatomy morphology palaeontology 11:1–41 28 madtsoiidae: monophyletic clade or grouping of convenience? mark j. powers1, fernando f. garberoglio2, and michael w. caldwell1 1department of biological sciences, university of alberta, edmonton, ab, t6g 2e9, canada; powers1@ualberta.ca 2conicet-fundación de historia natural félix de azara, centro de ciencias naturales ambientales y antropológicas, universidad maimónides, hidalgo 775, 1405 buenos aires, argentina madtsoiidae is currently defined as an extinct family of snakes that share several vertebral characteristics. they appeared in the late cretaceous of gondwana and reached a nearly global distribution by the eocene, frequently acquiring large body sizes and utilizing narrow intercontinental seaways for dispersal. early discovered specimens were referred to boiidae or pythonidae due to general similarities of vertebral proportions. however, frequent observations of several key vertebral features such as the absence of accessory prezygapophyseal processes, the presence of laterally expanded para-diapophyses and the presence of parazygantral foramina led to the hypothesis that madtsoiidae represents a valid clade of snakes. due to cranial material being quite rare, most named taxa within madtsoiidae are described from isolated or segments of articulated vertebrae, including the type species madtsoia bai from eocene deposits of the chubut province, argentina. because of the paucity of well-preserved specimens for madtsoiids, species diagnoses and phylogenetic relationships are resolved almost entirely on vertebral characters, which can show considerable variation along the vertebral column of an individual. the variability of madtsoiid synapomorphies across the vertebral column has not been critically assessed due to the lack of cervical (anterior trunk) and caudal (post-cloacal) vertebrae. an articulated series of madtsoiid cervicals from upper eocene deposits of the divisadero largo formation in the cuyo basin of the mendonza province, argentina, are referred to madtsoia sp. based on identified madtsoiid synapomoprhies (parazygantral foramina), age (mid-late eocene) and proximity to the holotype locality. comparison of this specimen to others from extinct and extant snake clades reveals a wide range of putative madtsoiid synapomophies are variably expressed in non-madtsoiid clades. the variability of these “synapomorphies” across a single vertebral series demonstrates problematic degrees of intraspecific variation when diagnosing isolated vertebrae. these observations reinforce the poor utility of vertebral characters in snake phylogenetics, and stress the importance of relatively complete specimens in constructing species diagnoses. vertebral pathology: a primer addressing its definitive features in the paleontological record bruce rothschild indiana university health, muncie, in, 47304, usa; spondylair@gmail.com with the increasing complexity of a skeletal system, more numerous are the opportunities for its structural integrity to be compromised. this is especially true for the vertebral column which consists of bones stabilized anteriorly/ventrally by their intervertebral anatomy and dorsally/posteriorly by zygapophyseal/facet joints. these two components are interdependent; alterations of one places stresses on the other, with the anticipated biomechanical response. vertebrae are predominantly, but not invariably, separated by discs in mammals, by diarthrodial (synovial lined) joints in lower vertebrates and are subject to both mechanical forces and hazards related to surrounding structures. vertebral pathology could potentially and not mutually exclusively be divided into bone loss and bone accretion. canadian society of vertebrate palaeontology 2023 abstracts 29 bone loss in the form of lysis or erosion is relatable to trauma, inflammatory arthritis infection, neoplasia, pressure phenomena and potentially osteoporosis (allowing vertebral collapse). the pressure phenomenon responsible for aneurysm formation can also leave a sharply defined imprint as can spondyloarthropathy and gout. infectious lesions tend to be less sharply defined, but it is the reactive filigree reaction and draining sinuses that allow confident diagnosis, at least of the “pyogenic” variety. space-occupying infections (often referred to as non-pyogenic or granulomatous) produce quasi-spheroid lesions, often with quite minimal bone response. specific among those is the endplate groove apparently related to brucellosis. neoplasia generally produces irregular-shaped damage, with residual normal trabeculae at edges. a major differential clue to distinguishing between infection and neoplasia is endplate involvement. neoplasia may affect multiple vertebrae but does not cross joint/disc spaces. last among the bone loss phenomena are the vertebral endplate depressions referred to as pressure derived schmörl’s nodes in mammals with intervertebral discs. most reptiles, however, seem to have synovia-lined cavities rather than discs separating/joining their vertebrae and thus their articular surface alterations represent erosions rather than pressure phenomena. differential considerations then are limited to inflammatory arthritis (e.g., spondyloarthropathy) and infectious arthritis. bone accretion is relatable to spondylosis deformans or osteoarthritis, inflammatory arthritis, infection, neoplasia and healing responses and paraspinal ligamentous [e.g., diffuse idiopathic skeletal hyperostosis (dish)] phenomena. endplate-derived overgrowths of bone that are perpendicular to the long axis of the vertebral column are referred to as osteophytes. if the vertebral endplates involved are separated by synovia-lined joints (diarthrodial), osteoarthritis is defined. since osteoarthritis is a disease of joints, it is not the appropriate term if the bones involved are not-so separated and the correct designation would be spondylosis deformans. with respect to fusion/ankylosis of vertebrae, any alteration that reduces joint stability may be associated with new bone formation that bridges the joint components, restoring stability. arthritis-related bridging, referred to as syndesmophytes, may appear as gracile or bulky bridging, always involving the edge of the vertebral endplate as well as ligamentous structures, in contrast to dish in which ossification is solely ligamentous. apposition of calcific material on endplate surfaces identifies calcium pyrophosphate depositional disease (cppd), an inflammatory arthritis. differential consideration includes what has been referred to as central osteophytes, a phenomenon in search of an explanation. as vertebrae are the “measure” of vertebrata, it seems appropriate to systematically examine related organismal “vulnerabilities” and to establish an epidemiological data base. a small early permian parareptile with a lateral temporal fenestra from richards spur, oklahoma dylan rowe, erin beauchesne, joseph bevitt, and robert reisz department of biology, university of toronto mississauga, toronto, on, canada a small, pristinely preserved specimen from the dolese brothers limestone quarry near richards spur, oklahoma provides evidence for the presence of a new early permian parareptile. the specimen includes an articulated, nearly complete skull roof with the right premaxilla, right quadratojugal and most of the right palate, as well as the right epipterygoid and the sphenethmoid. although similar in many respects to the other contemporary parareptiles acleistorhinus, delorhynchus and colobomycter from oklahoma, it can be distinguished from other acleistorhinids by the presence of autapomorphic dental characters. phylogenetic analysis places the specimen closer to delorhynchus and colobomycter within acleistorhinidae than to acleistorhinus pteroticus. unique aspects of the present specimen include the pronounced anterior extension of the lacrimal bone, largely homodont dentition composed of simple conical crowns with slight recurvature in the premaxillary and anterior maxillary teeth, vertebrate anatomy morphology palaeontology 11:1–41 30 and simple conical crowns in posterior maxillary dentition. the discovery of this new parareptile along with the large number of other parareptiles at richards spur highlights the importance of this site which has preserved a number of articulated specimens. this early permian site is unique in that it has such a wide diversity of parareptilian taxa and provides important insights into the complex community of these ancient terrestrial vertebrates. the present specimen highlights the morphological diversity among parareptilia occupying relatively similar niches within the locality of richards spur. a plesiosaur representing the first published vertebrate material from the foraminifera-dominated peace river formation, alberta, canada maximilian scott philip j. currie dinosaur museum, wembley, ab, t0h 3s0, canada; mscott@dinomusuem.ca a plesiosaur (reptilia, sauropterygia) catalogued in the collections of the philip j currie dinosaur museum, specimen pjcdm 2017.13.1, from the middle albian cadotte member represents the first published vertebrate material from the peace river formation of northwestern alberta. the peace river formation (lower cretaceous, albian stage) consists of sediments consistent with a shallow, coastal marine environment transitioning from an intertidal bay to a lower marine environment on the west coast of the western interior seaway. the specimen is represented by the impression of a section of three and a half articulated dorsal vertebrae (each measuring 7 cm in length and 5 cm in width at the center), 14 exposed partial gastralia, several impressions of missing gastralia, a partially broken left coracoid (measuring 40 cm in length), a faint impression of the lower center-facing portion of the right coracoid, and a concentration of gastroliths in the belly. the morphology of the coracoid, bearing an intercoracoid vacuity, is diagnostic to elasmosauridae, of an age comparable with only one named albertan elasmosaurid from the albian stage, wapuskanectes betsynichollsae. based on coracoid length, this individual is smaller than w. betsynichollsae, and the coracoid of this specimen is morphologically distinct from that of w. betsynichollsae given that the posterior end of the coracoids on the peace river specimen are unfused. the presence of a posterolateral cornua indicates the individual was ontogenetically mature at the time of death, unlike a morphologically similar specimen in the collections of the royal tyrrell museum of palaeontology from the lower albian clearwater formation of north-eastern alberta, tmp 1999.068.0001, which is less robust than pjcdm 2017.13.1 and lacks a posterolateral cornua. it is possible that pjcdm 2017.13.1 represents a new species of north american elasmosaurid given its morphological distinctness from similar-aged taxa, though may be taxonomically similar to the albian elasmosaur tmp 1999.068.0001. this specimen may also indicate the potential for future fossil discoveries from the peace river formation, which has historically been under-sampled for vertebrate material. canadian society of vertebrate palaeontology 2023 abstracts 31 duck-faced and eagle-eyed: a well-developed visual system in a high-latitude hadrosaur henry s. sharpe1, philip j. currie1, and corwin sullivan1,2 1department of biological sciences, university of alberta, edmonton, alberta, canada; hssharpe@ualberta.ca corwin1@ualberta.ca; pjcurrie@ualberta.ca 2philip j. currie dinosaur museum, wembley, ab, canada edmontosaurus is a large hadrosaurid dinosaur known from the campanian and maastrichtian of north america, with a biogeographic range spanning from the southern united states to the north slopes of alaska. edmontosaurus is distinguished from other hadrosaurids by the presence of a “pocket” in the postorbital bone, a large fossa expanding posteriorly and laterally from the orbit. three-dimensional cranial reconstruction of an e. regalis skull showed that development of the postorbital pocket displaced the posterior margin of the orbit laterally relative to the plesiomorphic condition. this likely gave edmontosaurus a degree of binocular overlap in its field of vision comparable to advanced tyrannosaurids. continuous resorption of the inner walls of the postorbital pocket even in the largest specimens of edmontosaurus renders identification of soft-tissue correlates problematic, and indicates continuous enlargement of this feature throughout adulthood. although the exact nature of the contents filling the postorbital pocket is unknown, the inner shape of the pocket resembles the external morphology of an expanded ophthalmic rete, a large thermoregulatory blood vessel plexus behind the eye in modern birds. the optic nerve foramina in e. annectens and e. regalis are significantly larger in cross-sectional area compared to braincase length than the typical hadrosaurid (e.g., hypacrosaurus, maiasaura) condition. edmontosaurus was likely able to see with better acuity and depth perception than other known hadrosaurids, adaptations that aid modern crepuscular and nocturnal birds and mammals in finding food in low-light conditions. edmontosaurus was capable of inhabiting high latitudes, where enhanced vision may have aided feeding during seasonal darkness. quantitative reconstruction of feeding mechanics in leptoceratops gracilis brown, 1914 using novel digital methods: a proof-of-concept emilia l. silvestre, louis-philippe bateman, and hans c.e. larsson mcgill university, montreal, qc, h3a 0c4, canada; emilia.silvestre@mail.mcgill.ca; louis-philippe.bateman@mail. mcgill.ca; hans.ce.larsson@mcgill.ca the study of functional morphology in dinosaurs and other extinct animals has traditionally been inhibited by a lack of reproducible methods. indeed, simulating the biomechanics of ancient creatures in silico is difficult and requires simultaneously considering the biomechanical effects of muscles and responses of a myriad of hard and soft tissues, positions of bones and muscles, and the presence of cartilage. digital methods are a promising alternative to practical methods. this study aims to serve as a proof-of-concept for high-precision surface scanning and biomechanical reconstructions. blender, a free open-source software that is becoming the scientific standard for organic 3d modelling, was used to reconstruct and assess the feeding system of the basal ceratopsian leptoceratops gracilis brown, 1914. vertebrate anatomy morphology palaeontology 11:1–41 32 the skull of leptoceratops gracilis (canadian museum of nature specimen cmn 8889) was surface scanned using a handheld 3d scanner. models generated from the scan were subsequently retrodeformed in blender. we reconstructed its bite cycle based on anatomical limits of the jaw joint, tooth and beak occlusion, and previously published research on the tooth microwear of this taxon (varriale 2016). in parallel, we digitally reconstructed all major jaw-closing musculature based on osteological correlates and previous reconstructions of ornithischian cranial musculature. two muscle arrangements were modelled according to competing hypotheses in the literature after holliday (2009) and nabavizadeh (2018). in addition, m. adductor mandibulae externus ventralis (mamev) and m. pseudomasseter (mpsm) were added to these models based on previous reconstructions that have been proposed in heterodontosaurus (mamev) and psittacosaurus (mamev and mpsm) (sereno 2012; sereno et al. 2010). following muscle reconstruction, we estimated the bite force of leptoceratops gracilis at various tooth positions for each model to quantitatively assess the efficiency of the feeding system. we discovered that the range of motion of the lower jaw did not restrict the jaw to simple orthal movements. instead, we found that the bite cycle was characterised by a two-part power stroke beginning with an orthal component that smoothly grades into a palinal component. our results are consistent with those of previous workers, which suggest that leptoceratops gracilis had a circumpalinal power stroke during its bite cycle (varriale 2016). we also discovered that known muscle physiology in conjunction with maximum gape could aid in constraining origin and insertion limits of some muscles. we found that, for our model following holliday (2009), the bite force of leptoceratops gracilis would have ranged from 550 n at the tip of the beak to 2520 n at the posterior-most tooth. for our model following nabavizadeh (2018), the bite force would have ranged from 590 n to 2650 n at the same positions. each muscle’s force contribution to bite force throughout the jaw closing cycle reveals a complex interplay between them. overall, this study is a powerful proof-of-concept for novel digital methods which have become increasingly used in paleontological research within the past decade. we have developed a complete methodology for surface-scanning complex fossil objects, editing them to anatomical correction, applying muscle vectors, and reconstructing their biomechanics in blender. this approach is fully modular, meaning that it could be applied to any living or extinct animal. we hope to extend this methodology to other neoceratopsians to examine the evolution of cranial musculature and chewing mechanics across this clade. literature cited holliday, c.m. 2009. new insights into dinosaur jaw muscle anatomy. the anatomical record 292:1246–1265. nabavizadeh, a. 2018. new reconstruction of cranial musculature in ornithischian dinosaurs: implications for feeding mechanisms and buccal anatomy. the anatomical record 303:247–362. sereno, p.c. 2012. taxonomy, morphology, masticatory function and phylogeny of heterodontosaurid dinosaurs. zookeys 226:1–225. sereno, p.c., z. xijin, and t. lin. 2010. a new psittacosaur from inner mongolia and the parrot-like structure and function of the psittacosaur skull. proceedings of the royal society b 277:199–209. varriale, f.j. 2016. dental microwear reveals mammal-like chewing in the neoceratopsian dinosaur leptoceratops gracilis. peerj 4:e2132. canadian society of vertebrate palaeontology 2023 abstracts 33 new and expanded preparation techniques from pipestone creek material leads to insights about this late cretaceous wapiti formation locality jackson sweder1, emily l. bamforth1,2, and maximilian scott1 1philip j. currie dinosaur museum, wembley, ab, t0h 3s0, canada; jsweder@dinomusuem.ca; curator@dinomusuem.ca; mscott@dinomuseum.ca 2department of geological sciences, university of saskatchewan, saskatoon, sk, s7n 5e2, canada the pipestone creek bonebed was discovered in the 1970’s and has contributed to the understanding of the late cretaceous (80 – 68 ma) wapiti formation of northwestern alberta and northeastern british columbia for 50 years (tanke 2006). this bonebed is one of the densest in north america, with up to 300 bones per square meter, and extends an estimated 5000 m2. the pipestone creek bonebed is dominantly monotaxic and represents a herd of the ceratopsian pachyrhinosaurus lakustai at several ontological stages (currie et al. 2008). alongside these large vertebrates, several other taxa are represented, including fossil turtles, reptiles, tyrannosaurid and dromaeosaurid teeth, and bones of the dromaeosaur boreonykus certekorum (bell and currie 2015). since late 2021, preparation of material from the pipestone creek bonebed has evolved to be more mindful of the non-macrovertebrate fauna and also flora. many fossil preparation labs incorporate screen washing of overburden matrix removed during the preparation process to locate micro-vertebrate fossils. this technique has proven difficult with the pipestone creek bonebed matrix, as it does not respond well to manual screen washing after the material is soaked in water. expanding the techniques to include constant agitation of the material during soaking has also resulted in limited success. however, the addition of hydrogen peroxide into the soaking solution and screen washing small samples with only hydrogen peroxide has yielded exciting results. examples of this new technique on the pipestone creek bonebed material has resulted in the discovery of fish and reptile material not previously found with traditional manual preparation and water soaking techniques. these new discoveries add to the understanding of the fossil locality and provide insights about the palaeoenvironment of this pipestone creek deposit. literature cited tanke, d.h. 2006. sixty years of pachyrhinosaurus (dinosauria: ceritopsidae) discoveries in north america; pp. 38–56 in: h. allen (ed.) alberta palaeontological society tenth annual symposium, abstracts. alberta palaeontological society, calgary, ab. currie, p.j., w. langston, jr., and d.h tanke. 2008. a new horned dinosaur from an upper cretaceous bone bed in alberta. nrc research press, ottawa, ontario, canada. 144 pp. bell, p. r., and p. j. currie. 2015. a high-latitude dromaeosaurid, boreonykus certekorum, gen. et sp. nov. (theropoda), from the upper campanian wapiti formation, west-central alberta. journal of vertebrate paleontology 36. doi 10.1080/02724634.2015.1034359 vertebrate anatomy morphology palaeontology 11:1–41 34 changes in emplacement pattern and organization of the palatal dentition accompanied the evolution of herbivory in edaphosauridae (synapsida, eupelycosauria) andrew l. traynor1, aaron r.h. leblanc2, and kenneth d. angielczyk3 1carleton university, ottawa, on, k1s 5b6, canada; andrewtraynor@cmail.carleton.ca 2king’s college london, london, uk; arl@ualberta.ca 3negaunee integrative research center, field museum of natural history, chicago, il, 60605, usa; kangielczyk@ fieldmuseum.org although palatal dentition is a ubiquitous trait among early tetrapods, many major amniote lineages display a tendency towards its reduction. however, among the earliest synapsids (i.e., ‘pelycosaurs’), edaphosaurids uniquely elaborated the palatal dentition, interpreted as one of an array of cranial specializations (e.g., palinal jaw movement, high mechanical advantage of the jaw, and accommodations for large adductor jaw muscles) resulting from the evolution of high-fiber herbivory. although previous studies have detailed the gross morphological trends of the palatal dentition among pelycosaurs, there has been little consideration of the extent to which feeding strategy correlates with changes in the developmental processes that governed the organization of the palatal dentition. we assessed μct scans of the palatal dentition of edaphosaurus novomexicanus and the ophiacodontid varanosaurus acutirostris using indicators of emplacement patterns first outlined for captorhinus aguti, a contemporaneous eureptilian taxon with a similarly arranged and implanted marginal dentition. emplacement indicators include the cross-cutting relationships of teeth (i.e., when a newly-formed tooth causes partial resorption of an existing tooth), relative tooth size, and the location of emplacement pits on tooth-bearing element. together, these indicators facilitate the recognition of vectors of tooth addition that inform broader organization of the palatal dentition. there is little pattern to emplacement in v. acutirostris and instances of cross-cutting relationships are rare, suggesting its denticle fields lacked strict organization. we consider the state in v. acutirostris to be representative of the ancestral pelycosaur condition. conversely, the presence of a clear pattern of palatal tooth addition and numerous instances of cross-cutting relationships in e. novomexicanus indicate a greater level of organization of its denticle fields and a potentially higher rate of tooth emplacement. a higher level of organization was likely an important component of the elaboration of the denticle fields in edpahosaurus for use in oral processing of food as part of its herbivorous diet. there is a trend toward increased numbers of denticles in derived edaphosaurus species, and future research should investigate whether they were accompanied by further refinements to emplacement patterns. the increased organization of the palatal dentition in e. novomexicanus demonstrates that the evolution of high-fiber herbivory not only effected changes to the morphology of the palatal dentition, but also to the developmental processes governing its formation. funding: university of chicago department of ecology and evolution undergraduate fellowship canadian society of vertebrate palaeontology 2023 abstracts 35 evaluation of enamel microstructures in small theropod dinosaurs ashley verstraete1, derek w. larson2, and kirstin s. brink1 1department of earth sciences, university of manitoba, winnipeg, mb, r3t 2n2, canada; verstraa@myumanitoba.ca; kirstin.brink@umanitoba.ca 2research and collections management department, royal british columbia museum, victoria, bc, v8w 9w2, canada; dlarson@royalbcmuseum.bc.ca the theropod dinosaurs known from the cretaceous dinosaur park formation (dpf), alberta, include several taxa erected based solely on isolated teeth. with the recent discovery of articulated specimens of saurornitholestes langstoni preserving the tooth taxon zapsalis abradens, it is possible that other “tooth taxa” are also part of the heterodont dentitions of small dinosaurs and not individual species, or may even belong to other archosaur groups. therefore, our understanding of archosaur diversity in the dpf might be skewed towards theropods. previous studies of enamel microstructures in dinosaurs have shown species-specific traits that may be useful for taxonomic identifications. in this study, we examined the enamel microstructure of eight small theropod tooth morphotypes that have previously been regarded as being separate species from the dpf to determine the distribution of enamel microstructure characters, including both morphotypes of s. langstoni. we also examined the enamel microstructure of two pterosaur species from the cenomanian kem kem beds of morocco for a comparison to small theropod enamel microstructure. these data allowed us to determine which enamel microstructure characters are useful for determining shared ancestry, or if enamel microstructure depends more on tooth shape and thus is determined by tooth function. we sectioned the teeth in transverse and longitudinal planes and examined the microstructures with a scanning electron microscope. results show that no major taxonomically informative patterns in enamel microstructure among the theropods and pterosaurs examined here. the archosaurs in this study all had parallel enamel with basal unit layers, and many with incremental lines. the heterodont teeth of saurornitholestes show differences in the positioning of incremental lines,crystallite sizes, and the presence of tubules, suggesting enamel microstructure is reflective of tooth shape and function based on its position in the mouth. this study concludes that enamel microstructure is less useful for taxonomic identification than previously thought, especially for lower-level taxonomic comparisons and archosaurs that share relatively thin, simple enamel. enamel microstructure is likely linked to tooth function and placement in the mouth of an organism and less-so to evolutionary history. vertebrate anatomy morphology palaeontology 11:1–41 36 redescription of a juvenile hadrosaurid from the upper cretaceous of alberta using computed tomography trystan m. warnock-juteau1, michael j. ryan1,2, r. timothy patterson1, and jordan c. mallon1,2 1department of earth sciences, carleton university, ottawa, on, k1s 5b6, canada; trystanwarnockjuteau@cmail. carleton.ca; michaelj.ryan@carleton.ca; tim.patterson@carleton.ca 2palaeobiology, canadian museum of nature, ottawa, on, k1p 6p4, canada; jmallon@nature.ca canadian museum of nature specimen cmn 8917 is a partial skull originally described by charles m. sternberg (1956) that is one of only several nestling-sized, juvenile hadrosaurines known to date. sternberg’s original description of the specimen was limited to what was visible externally. we report here on new data obtained using computed tomography (ct) to create 3d models of individual skull elements, allowing for a more thorough description and precise identification of the specimen. support for its placement within hadrosaurinae includes the presence of an anterodorsal maxillary process, a maxillary dorsal process that is anteroposteriorly wider than dorsoventrally tall, and a narial vestibule not enclosed within the premaxillary dorsal and lateral processes. the skull also possesses two tooth traits traditionally associated with lambeosaurines (horner et al. 2004) — secondary ridges on the maxillary and dentary crowns, and denticulation on some of the maxillary crowns. the occurrence of these features in a juvenile hadrosaurine suggests that they are modified during ontogeny, thus calling into question their utility for the taxonomic identification of juvenile specimens. the morphology of the occlusal surface on the dentary teeth of cmn 8917 is similar to those of late nestlings of the hadrosaurine maiasaura peeblesorum (horner et al. 2000; prieto-márquez and guenther 2018) and those of many adult hadrosaurids (erickson et al. 2012), possessing a concave occlusal surface with steeper lingual and shallower buccal wear zones. this differs from the morphology of hatchling lambeosaurine hypacrosaurus stebingeri, which possess shallow-angle cup-shaped occlusal surfaces (erickson and zelenitsky 2014). differences in occlusal surface morphology between cmn 8917 and h. stebingeri (erickson and zelenitsky 2014) at early ontogenetic stages suggests interspecific differences in dental battery development, possibly reflective of dietary differences early in ontogeny. literature cited erickson, g.m., b.a. krick, m. hamilton, g.r. bourne, m.a. norell, e. lilleodden, and w.g. sawyer. 2012. complex dental structure and wear biomechanics in hadrosaurid dinosaurs. science (american association for the advancement of science) 228:98–101. erickson, g.m. and d. zelenitsky. 2014. osteohistology and occlusal morphology of hypacrosaurus stebingeri teeth throughout ontogeny with comments on wear-induced form and function; pp. 422–432 in: d.a. eberth and d.c. evans (eds.), hadrosaurs. indiana university press, bloomington, in, usa. horner, j.r., a. de ricqlès, and k. padian. 2000. long bone histology of the hadrosaurid dinosaur maiasaura peeblesorum: growth dynamics and physiology based on an ontogenetic series of skeletal elements. journal of vertebrate paleontology 20:115–129. horner, j. r., d.b. weishampel, and c.a. forster. 2004. hadrosauridae; pp 438–463 in d.b. weishampel, p. dodson, and h. osmólska (eds.), the dinosauria 2nd edition. university of california press ltd, london, uk. prieto-márquez, a., and m.f. guenther. 2018. perinatal specimens of maiasaura from the upper cretaceous of montana (usa): insights into the early ontogeny of saurolophine hadrosaurid dinosaurs. peer j 6. sternberg, c.m. 1956. a juvenile hadrosaur from the oldman formation of alberta. bulletin no. 136. annual report of the national museum for the fiscal year 1953–54 136:120–122. canadian society of vertebrate palaeontology 2023 abstracts 37 isotope palaeoecology of duck-billed dinosaurs (ornithischia: hadrosauridae) from the upper campanian dinosaur park formation joshua wasserlauf1, jordan mallon1,2, thomas cullen3, françois therrien⁴, brian cousens1, and clément bataille⁵ 1carleton university department of earth sciences, ottawa, on, k1s 5b6, canada; joshuawasserlauf@cmail.carleton.ca; briancousens@cunet.carleton.ca 2beaty centre for species discovery and palaeobiology section, canadian museum of nature, ottawa, on, k1p 6p4, canada; jmallon@nature.ca 3auburn university department of geosciences, auburn, al, 36849, usa; thomas.cullen11@gmail.com ⁴royal tyrrell museum of palaeontology, drumheller, ab, t0j 0y0, canada; francois.therrien@gov.ab.ca ⁵department of earth sciences, university of ottawa, ottawa, on, k1n 6n5, canada; cbataill@uottawa.ca size-frequency distributions of north american hadrosaurid bone-beds reveal possible behavioural differences between juvenile to sub-adult/adult stages. bonebed data suggest that juvenile hadrosaurids may have lived in separate groups isolated from adults and subadults. moreover, the co-occurrence and similar morphology between hadrosaurid sub-families (hadrosaurinae and lambeosaurinae) has led to questions regarding their ecology, diets, and potential competition. detecting ecological behaviors and habitat use patterns can be difficult using morphological data alone, and although the morphology of vertebrate bones remains a useful palaeoecological indicator, recently there has been increased emphasis on augmenting these indicators with the inclusion of morphology-free approaches to palaeoecological analyses, including isotope geochemistry. isotopic proxies such as δ13c, δ18o, and 87sr/86sr, provide valuable insights into a fossil organism’s ancient living conditions, potential feeding habits, and geographical pathways of migration. aspects of migration and range size, dietary specializations, and growth in hadrosaurid dinosaurs can therefore be revealed using isotope geochemistry to convey how these animals coexisted and to test how their ecological niche shifted in an ontogenetic context. in this study, we measured isotope composition in hadrosaurid tooth enamel from several individuals from the dinosaur park formation, of various ages and sub-familial affinities, to test for differences in the palaeoecology of hadrosaurines and lambeosaurines, as well as for changes in the ecology of these animals through ontogeny. because hadrosaurid dental batteries contain multiple generations of teeth, formed across multiple years, sampling the growth record of these teeth allows seasonal, annual, and multi-year patterns to be recorded. preliminary analyses of the enamel isotopic signatures reveal a detectable shift in average 87sr/86sr, δ18o, and δ13c from juveniles to adults, both in absolute values and in the amount of dispersion around each value. ranges for δ13c, δ18o, and 87sr/86sr signals are considerably more constrained in the juvenile samples than in values obtained for adults. greater dispersion in 87sr/86sr and δ18o ranges in both lambeosaurine and hadrosaurine adults may indicate a shift to more widespread/wide-ranging feeding behaviours. the analysed juvenile specimen exhibits a more positive mean δ13c (-0.10‰ vpdb vs -3.40‰ vpdb in adults) than the adults, contrary to a predicted depletion in the signal consistent with feeding on plants under dense canopy, but potentially related to or offset by other habitat factors such as feeding on more osmotically stressed plants in coastal forest/mangrove forest settings. finally, we observe distinct seasonal profiles of δ13c and δ18o between hadrosaurines and lambeosaurines, with some specimens demonstrating positive correlations between these two signals and others exhibiting an inverse correlation. these findings may reflect divergent use of landscape and habitat resources between the two sub-families. vertebrate anatomy morphology palaeontology 11:1–41 38 a new archosaurian skeleton from the middle triassic of china: shedding light on the phylogenetic position of wangisuchus (pseudosuchia, gracilisuchidae) xiao-chun wu1, zhi-shuai kang2, li-yang dong2, jian-ru shi2, and hai-lu you3 1beaty centre for species discovery and palaeobiology section, canadian museum of nature, ottawa, on, k1p 6p4, canada; xcwu@nature.ca 2shanxi museum of geology, binhexilu zhongduan, taiyuan, shanxi 030024, china; sxdzbwgkzs@163.com; ryyuunang_919@yeah.net; shijianru@126.com 3key laboratory of vertebrate evolution and human origins, institute of vertebrate paleontology and paleoanthropology, chinese academy of sciences, beijing, 100044, china; youhailu@ivpp.ac.cn wangisuchus young, 1964 is a monospecific genus. its type species, wangisuchus tzeyii young 1964, was established mainly based on four incomplete maxillae from the upper ermaying formation (middle triassic) near louzeyu village of wuxiang county, shanxi province, china. of the four maxillae, one was appointed as the holotype (in the collections of the institute for vertebrate paleontology and paleoanthropoloyg, ivpp v 2701) and the other three as the paratypes (ivpp v 2702 to 2704) of the species. at the same time, young (1964) also assigned many incomplete postcranial elements to the species. most of the assigned specimens came from the same quarry where the type and paratypes were excavated. young (1964) placed w. tzeyii in euparkeridae (v. huene 1920). sennikov (1989) referred w. tzeyii (with halazhaisuchus qiaoensis wu, 1982, and turfanosuchus shageduensis wu, 1982) to the putative euparkeriid subgroup dorosuchinae along with dorosuchus neoetus from russia. lucas (2001) also considered the chinese taxa as euparkeriids. some other studies (kuhn 1976; parrish 1993; gower and sennikov 2000; nesbitt 2011) argued that only the holotype could represent w. tzeyi. sookias et al. (2014) restudied the material of w. tzeyi and considered w. tzeyi as a nomen dubium due to the absence of any feature that can diagnose the holotype and the lack of any convincing evidence that the previously referred additional specimens represent the same taxon as the holotype. since w. tzeyi was established, it has not been included in any phylogenetic study on archosaurians due to its fragmentary nature. after examining the material of young (1964), we consider one (ivpp v 2704) of the three paratypes as also belonging to w. tzeyi based on the antorbital fossa that extends along the dorsolateral margin of the maxilla as in the type specimen. in 2013, a field team of shanxi musuem of geology (sxmg) collected an archosaurian skeleton (sxmg v2014) from the upper ermaying formation at a site which is about 11 km northwest to the locality where the type and paratypes of w. tzeyi were collected. in 2019, we conducted fieldwork around the fossil locality in wuxiang county. according to our stratigraphical correlation, the new and type localities of w. tzeyi are roughly situated in the same horizon of the upper ermaying formation. most parts of the new archosaurian skeleton are well-preserved but the posterior section of the tail is missing. we refer the new archosaurian skeleton to w. tzeyi based on characters from the maxilla (characters 1 and 2 below). with the new specimen, w. tzeyi can be diagnosed by a set of characters, the most important of which include 1) the antorbital fossa extending onto the dorsolateral side of the maxilla, 2) the orbit anteroposteriorly shorter than the antorbital fenestra, 3) the maxilla possessing a posterodorsal process around the posteroventral corner of the antorbital fenestra, 4) the jugal terminating before the posteroventral margin of the lower temporal fenestra, 5) the height of the scapular nearly equal to the humeral length, 6) the humerus and ulna nearly same in length, and 7) the postacetabular process of the ilium trunked posteriorly. canadian society of vertebrate palaeontology 2023 abstracts 39 in our phylogeny analysis, we coded w. tzeyi based on the new skeleton into the data set used by lecuona et al. (2017). our preliminary results suggest that w. tzeyi is a gracilisuchid and supports the monophyly of gracilisuchidae. our new analysis suggests that turfanosuchus dabanensis and w. tzeyi form a set of successive sister-groups towards the gracilisuchus stipanicicorum–yonghesuchus sangbiensis clade within the family. the discovery of the new archosaurian skeleton not only established the phylogenetic relationships of w. tzeyi for the first time but also indicates that the clade gracilisuchidae originated in what is now china during the middle triassic. literature cited gower, d.j. and a.g. sennikov. 2000. early archosaurs from russia; pp. 140–159 in m.j. benton, m.a. shishkin, d.m. unwin, and e.n. kurochkin, (eds.), the age of dinosaurs in russia and mongolia. cambridge university press, new york. huene, f. v. 1920. osteologie von aetosaurus ferratus o. fraas. acta zoologica 1:465–491. kuhn, o. 1976. handbuch der paläherpetologie. gustav fischer verlag, stuttgart/new york, 137 pp. lecuona, a., j.b. desojo, and d. pol. 2017. new information on the postcranial skeleton of gracilisuchus stipanicicorum (archosauria: suchia) and reappraisal of its phylogenetic position. zoological journal of the linnean society 181:638– 677. doi 10.1093/zoolinnean/zlx011. lucas, s.g. 2001. chinese fossil vertebrates. columbia university press, new york, 376 pp. nesbitt, s.j. 2011. the early evolution of archosaurs: relationships and the origin of major clades. bulletin of the american museum of natural history 352:1–292. doi 10.1206/352.1. parrish, m.j. 1993. phylogeny of the crocodylotarsi, with reference to archosaurian and crurotarsan monophyly. journal of vertebrate paleontology 13:287–308. doi 10.1080/02724634.1993.10011511. sennikov, a.g. 1989. novyy euparkeriid (thecodontia) iz srednego triasa yuzhnogo priuralya. paleontologicheskii zhurnal. 1989:71–78. sookias, r.b., c. sullivan, j. liu, and r.j. butler. 2014. systematics of putative euparkeriids (diapsida: archosauriformes) from the triassic of china. peerj 2: e658. doi 10.7717/peerj.658. wu, x.-c. 1982. the pseudosuchian reptiles from shan-gan-ning basin. vertebrata palasiatica 20:289–301 (in chinese with english summary). young, c.c. 1964. the pseudosuchians in china. palaeontologia sinica 151:1–205 (in chinese and english). hadrosaurid skull from the wapiti formation preserves evidence of new feeding behaviours in tyrannosaurids taia c.a. wyenberg-henzler1, nicolas e. campione2, phil r. bell2, and corwin sullivan1,3 1department of biological sciences, university of alberta, edmonton, ab, canada; wyenberg@ualberta.ca; corwin1@ ualberta.ca 2school of environmental and rural science, university of new england, armidale, nsw, australia; pbell@une.edu.au; ncampion@une.edu.au 3philip j. currie dinosaur museum, wembley, ab, canada marks left on bone due to tooth-to-bone contact (i.e., tooth marks) represent direct evidence of behaviour in extinct vertebrates, particularly carnivores. in theropod dinosaurs, tooth marks have been used to infer behavvertebrate anatomy morphology palaeontology 11:1–41 40 iours such as intraspecific combat and carcass defleshing. here, we report an almost complete, articulated adult hadrosaurid skull (university of alberta laboratory for vertebrate palaeontology collections, specimen ualvp 60000) from the upper cretaceous (campanian–maastrichtian) wapiti formation of northern alberta, which bears tooth marks and other signs of damage. damaged surfaces that could potentially represent tooth marks were sampled using smooth-on dragon skin 10 very fast silicone. tooth marks were then identified using these silicone peels, based on similarities in shape and texture to tooth marks previously described in the literature. a total of 38 tooth marks were identified on ualvp 60000, ~87% of which are on the left, less intact side of the skull. by contrast, the right side of the skull is almost pristine below the crest, suggesting that this side of the head was likely resting on or even embedded in the substrate following the animal’s death. most of the tooth marks are oriented in an anteroposterior to posteroventral-anterodorsal direction on the portions of the premaxillae anterior to the orbits, and the anterior portions of the maxillae. the deepest tooth marks are on the anterior end of the left maxilla. one posterodorsally-anteroventrally oriented tooth mark is on the posterior end of the left maxilla, and two tooth marks are on the anterior end of the palatal surface of the right premaxilla. based on their location, spacing, and orientation, the tooth marks in the snout region were likely produced by a tyrannosaurid attempting to manipulate the skull from multiple angles. in particular, the deepest tooth marks are posterodorsally convex and anteroposteriorly oriented, and are interpreted as resulting from forceful attempts to either tear away the upper jaw for better access to the mouth cavity or roll/reposition the head. the single mark observed on the lateral surface of the posterior end of the left maxilla was likely produced when the tyrannosaurid was removing the nearby adductor musculature, such as the m. pseudotemporalis superficialis. consumption of adductor musculature likely also resulted in the incidental removal or deliberate destruction of the left jugal, quadratojugal, and quadrate. to our knowledge, ualvp 60000 is the first formally reported example of a hadrosaurid skull showing evidence of powerful and repeated attempts at manipulation by a tyrannosaurid. investigating genetic mechanisms of early limb development in ambystoma mexicanum and xenopus laevis jeffrey a. yee1,2, tetsuto miyashita1,2, and hillary c. maddin1 1earth sciences deptartment,carleton university, ottawa, on, k1s 5b6, canada; jeffreyyee@cmail.carleton.ca; hillarymaddin@cunet.carleton.ca 2palaeobiology, canadian museum of nature, ottawa, on, k1p 6p4, canada; tmiyashita@nature.ca varying in body-axis placement and developmental timing, tetrapod limbs are highly specialized, but conserved homologous structures. in the case of most amniotes, limbs are completely patterned during gestation. in contrast, amphibians provide a useful model for studying early limb development, as they develop limbs as free-living larvae. the genes and regulatory mechanisms of early limb development are ostensibly conserved across vertebrate species. previous work has found that a genetic element controlling early hindlimb development, hindlimb enhancer b (hleb), maintains functionality and drives the same mechanism across vertebrate groups. however, experiments demonstrating this have only been performed in mouse, and used hleb orthologues from python bivittatus, danio rerio, and anolis sagrei. under the hypothesis of hleb being a universal marker of vertebrate hindlimb development, we investigate the function of hleb in the extant amphibian species ambystoma mexicanum, and xenopus laevis via reciprocal reporter assay. this is a method wherein we introduce a transgene containing hleb and a fluorescent protein. using gfp as our reporter, we infer locations where hleb is active canadian society of vertebrate palaeontology 2023 abstracts 41 by observing patterns of fluorescence. early fluorescence of a x. laevis transgene in a. mexicanum suggests that hleb may maintain spatial function across amphibian species in a similar manner as previous work. while we have observed some fluorescence in transgenic a. mexicanum, we also consider that we will need a greater sample size to justify our conclusion, and that naturally fluorescent cell populations in a. mexicanum may obscure fluorescence truly generated by our transgene. notwithstanding our current limitations, our work will allow us to refine hypotheses of limb development mechanisms in ancestral tetrapods, and perhaps vertebrates.