GEOLOGY OF THE INTERMOUNTAIN WEST an open-access journal of the Utah Geological Association ISSN 2380-7601 Volume 7 2020 © 2020 Utah Geological Association. All rights reserved. For permission to copy and distribute, see the following page or visit the UGA website at www.utahgeology.org for information. Email inquiries to GIW@utahgeology.org. AN UNUSUALLY DIVERSE NORTHERN BIOTA FROM THE MORRISON FORMATION (UPPER JURASSIC), BLACK HILLS, WYOMING John R. Foster, Darrin C. Pagnac, and ReBecca K. Hunt-Foster Theme Issue An Ecosystem We Thought We Knew— The Emerging Complexities of the Morrison Formation SOCIETY OF VERTEBRATE PALEONTOLOGY Annual Meeting, October 26 – 29, 2016 Grand America Hotel Salt Lake City, Utah, USA GEOLOGY OF THE INTERMOUNTAIN WEST an open-access journal of the Utah Geological Association ISSN 2380-7601 Production Cover Design and Desktop Publishing Douglas A. Sprinkel Cover A few of the elements from the Little Hous- ton Quarry biota represented by individual fossils. Left to right and by approximate row top to bottom: Nanosaurus femur; seed; dromaeosaurid tooth; unionid bivalve shell imprint; salamander vertebra; Nanosaurus tooth; Docodon jaw; Theriosuchus jaw; abelisauroid(?) tooth; and Cteniogenys jaw. i Become a member of the UGA to help support the work of the Association and receive notices for monthly meetings, annual field conferences, and new publi- cations. Annual membership is $20 and annual student membership is only $5. Visit the UGA website at www.utahgeology.org for information and membership application. The UGA board is elected annually by a voting process through UGA members. However, the UGA is a volunteer-driven organization, and we welcome your voluntary service. If you would like to participate please contact the current president or committee member corresponding with the area in which you would like to volunteer. Utah Geological Association formed in 1970 from a merger of the Utah Geological Society, founded in 1946, and the Intermountain Association of Geologists, founded in 1949. Affiliated with the American Association of Petroleum Geologists. Volume 7 2020 This is an open-access article in which the Utah Geological Association permits unrestricted use, distribution, and reproduction of text and figures that are not noted as copyrighted, provided the original author and source are credited. Editors Society of Vertebrate Paleontology Editors Kelli C. Trujillo — University of Wyoming Cary Woodruff — University of Toronto Octavio Mateus — Universidade Nova de Lisboa Douglas A. Sprinkel Azteca Geosolutions 801.391.1977 GIW@utahgeology.org dsprinkel@gmail.com Bart J. Kowallis Brigham Young University 801.422.2467 bkowallis@gmail.com Steven Schamel GeoX Consulting, Inc. 801.583-1146 geox-slc@comcast.net Thomas C. Chidsey, Jr. Utah Geological Survey 801.537.3364 tomchidsey@utah.gov John R. Foster Utah Field House of Natural History State Park Museum 435.789.3799 johnfoster@utah.gov UGA Board 2020 President Leslie Heppler lheppler@utah.gov 801.538.5257 2020 President-Elect Riley Brinkerhoff riley.brinkerhoff@gmail.com 406.839.1375 2020 Program Chair Paul Inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 2020 Treasurer Greg Gavin greg@loughlinwater.com 801.538.4779 2020 Secretary Elliot Jagniecki ejagniecki@utah.gov 801.537.3370 2020 Past President Peter Nielsen peternielsen@utah.gov 801.537.3359 UGA Committees Education/Scholarship Zack Anderson zanderson@utah.gov 801.538.4779 Environmental Affairs Craig Eaton eaton@ihi-env.com 801.633.9396 Geologic Road Sign Greg Gavin greg@loughlinwater.com 801.541.6258 Historian Paul Anderson paul@pbageo.com 801.364.6613 Membership Rick Ford rford@weber.edu 801.626.6942 Outreach Greg Nielsen gnielsen@weber.edu 801.626.6394 Public Education Paul Jewell pwjewell@mines.utah.edu 801.581.6636 Matt Affolter gfl247@yahoo.com Publications Paul Inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 Publicity Paul Inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 Social/Recreation Roger Bon rogerbon@xmission.com 801.942.0533 AAPG House of Delegates 2017–2020 Term Tom Chidsey tomchidsey@utah.gov 801.537.3364 State Mapping Advisory Committee UGA Representative Bill Loughlin bill@loughlinwater.com 435.649.4005 Earthquake Safety Committee Chair Grant Willis gwillis@utah.gov 801.537.3355 UGA Newsletter Newsletter Editor Bill Lund uga.newsletter@gmail.com 435.590.1338 UGA Website — www.utahgeology.org Webmaster Paul Inkenbrandt paulinkenbrandt@utah.gov 801.537.3361 GEOLOGY OF THE INTERMOUNTAIN WEST an open-access journal of the Utah Geological Association Volume 7 2020 29 ABSTRACT The Little Houston Quarry in the Black Hills of Wyoming contains the most diverse vertebrate fauna in the Morrison Formation (Upper Jurassic) north of Como Bluff and the second-most diverse in the entire formation, after Reed’s Quarry 9. The deposit was an occasionally reactivated abandoned river channel, in interbedded green mudstone and laminated green-gray siltstone above a channel sandstone. The di- nosaur material is densely distributed and is disarticulated to articulated, with several associated skele- tons. The biota contains charophytes, horsetails, a possible seed fern, possible conifers, gastropods, two types of unionoid bivalves, diplostracans (“conchostracans”), a malacostracan, ray-finned fish, lungfish, a frog, salamanders, two types of turtles, rhynchocephalians, a lizard, choristoderes, two types of crocodyli- forms, a pterosaur, Allosaurus and several types of small theropods including Tanycolagreus? and probable dromaeosaurids, numerous Camarasaurus and a diplodocine sauropod, a stegosaur, the neornithischian Nanosaurus, and the mammals Docodon, Amblotherium, and a multituberculate. Among these taxa, one of the unionoid bivalves, an atoposaurid crocodyliform, and the species of Amblotherium, which appear to be new and unique to the locality so far. The Docodon material may represent the first occurrence of D. apoxys outside of its type area in Colorado. Additionally, small, unusual theropod tooth types reported here may represent the first Late Jurassic occurrence of cf. Richardoestesia in North America and a possible abelisauroid, respectively. An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming John R. Foster1, Darrin C. Pagnac2, and ReBecca K. Hunt-Foster3 1Utah Field House of Natural History State Park Museum, 496 East Main St., Vernal, UT 84078; johnfoster@utah.gov 2Museum of Geology, South Dakota School of Mines and Technology, 501 East St. Joseph, Rapid City, SD 57701 3Dinosaur National Monument, P.O. Box 128, Jensen, UT 84035 Citation for this article. Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K., 2020, An unusually diverse northern biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming: Geology of the Intermountain West, v. 7, p. 29–67, https://doi.org/10.31711/giw.v7.pp29–67. © 2020 Utah Geological Association. All rights reserved. For permission to use, copy, or distribute see the preceeding page or the UGA website, www.utahgeology.org, for information. Email inquiries to GIW@utahgeology.org. INTRODUCTION The Morrison Formation (Upper Jurassic) has been known as a massively productive unit for large dino- saurs since the second half of the nineteenth centu- ry (Dodson and others, 1980; Ostrom and McIntosh, 1999). Microvertebrate taxa were identified in the for- mation relatively early on (Marsh, 1879; Gilmore, 1910, 1928) but large samples of such taxa were restricted to only a handful of sites until relatively recently. Work from the past few years has suggested that microver- tebrate taxa, and specifically aquatic and semi-aquat- ic taxa, may be more abundant in the formation than commonly appreciated (Foster and Trujillo, 2004; Fos- ter and Heckert, 2011; Foster and McMullen, 2017) and that the Morrison may show some paleobiogeographic zonation based on these small taxa and their preferred environments for habitat and preservation (Chure and Evans, 1998; Foster and Trujillo, 2000; Foster and oth- ers, 2006; Foster and McMullen, 2017). Paleobiogeo- 30 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 graphic zonation is also becoming apparent for some groups of dinosaurs within the Morrison. The Black Hills have yielded Morrison Forma- tion taxa since O.C. Marsh (1890a) described the first specimen of Barosaurus, which had been partially collected by Marsh with J.B. Hatcher in 1889 (Marsh sent G.R. Wieland to collect more of the specimen in 1898). Smithsonian (USNM) and American Museum (AMNH) crews collected diplodocid and camarasaurid specimens from the Sturgis, South Dakota, area around 1900–1901, and the South Dakota School of Mines and Technology (SDSM) collected mostly sauropod materi- al from sites near Spearfish and Blackhawk, South Da- kota, and adjacent to Inyan Kara Creek in Wyoming, although theropods, turtles, and crocodyliforms were found at some sites (Foster, 1996a, 1996b; Foster and Chure, 2000). More than a dozen vertebrate localities are now known from the Black Hills (Foster, 1992, 1996a, 1996b, 2003; Maltese and others, 2018), and the most productive of these so far is the Little Houston Quarry, west of Sundance in Crook County, Wyoming (figure 1; Foster, 1993, 2001; Foster and Martin, 1994). The Little Houston Quarry was first developed in June 1991 and was worked annually through 2000 by the SDSM and from 2004–2011 by SDSM and the Museums of West- ern Colorado. The most diverse fauna of vertebrates known from the northern part of the Morrison Forma- tion is found in the Little Houston Quarry. This paper describes the richness of that fauna and several unique taxa from it that may be endemic to northern parts of the formation minimally and possibly to the Black Hills specifically. INSTITUTIONAL ABBREVIATIONS AMNH–American Museum of Natural History, New York, New York; FMNH–Field Museum of Natural History, Chicago, Illinois; MWC–Museums of Western Colorado, Dinosaur Journey, Fruita, Colorado; SDSM– South Dakota School of Mines and Technology, Mu- seum of Geology, Rapid City, South Dakota; USNM– National Museum of Natural History, Smithsonian Institution, Washington, D.C.; EBG–Field numbers of Darrin Pagnac for 1996–2000 field seasons, uncata- logued material at SDSM; JRF–Field numbers of John Foster for 1991–2000 field seasons, uncatalogued mate- rial at SDSM. GEOLOGIC SETTING AND LOCALITY The Morrison Formation in the northwestern Black Hills is unusually thin (~24 m; Mapel and Pillmore, 1963) compared to most outcrops of the unit farther south and west, and it consists of red, gray, and green, non-smectitic mudstones (Tank, 1956) with only a few thin, lenticular and laterally restricted sandstone beds (Foster, 1992; Turner and Peterson, 1999). In the eastern and southeastern Black Hills the lower member of the formation consists of an eolian sandstone (the Unkpapa Sandstone Member; Szigeti and Fox, 1981) that is over- I-25 I-90 W YO M IN G LHQ Site 50 km Wyoming SO U TH D A KO TA Jackson Laramie Sheridan Casper SundanceGillette Devils Tower NM Newcastle I-90 Figure 1. Location of the Little Houston Quarry (red star) on the northwestern edge of the Black Hills in Crook Coun- ty, northeastern Wyoming, and within the United States. 31 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 lain by an unnamed light gray to green silty mudstone facies that probably represents wet environments bor- dering the Unkpapa dune field to the south. Most of the fossil sites in the Morrison of the eastern and southeast- ern Black Hills occur in this latter facies (Foster, 1996b). In the northwestern Black Hills, the red, gray, and green mudstones have a more “traditional” appearance for the Morrison Formation, aside from the overall thinness, the lack of smectitic mudstones, and the very thin and restricted channel sandstones (Foster, 1992; Foster and Martin, 1994). The Little Houston Quarry consists of two pits, the main and mammal (figures 2A, 3A, and 3B), in the same abandoned channel deposit, separated laterally by approximately 70 m but easily correlated visually, as the channel cut down into variegated mudstones exposed on either side (Foster and Martin, 1994). The matrix of the quarry is an interbedded interval of green claystone and thinly laminated siltstone with abundant bone frag- ments and clayballs (figure 2B), which rests immediate- ly above a thin, convex-bottomed channel sandstone. Laterally, the deposit matrix and the bone material are Figure 2. (A) The south (main) pit of the Little Houston Quarry in the Morrison Formation of the Black Hills. The north (mammal) pit was illustrated as a cover photo in Foster (2018). (B) Interbedded green mudstone and lighter green-gray lam- inated siltstone (with lens cap for scale) of the Little Houston Quarry above a thicker siltstone interval containing a sauropod humerus. (C) Ilium and metatarsal of an associated juvenile Allosaurus jimmadseni skeleton (see Foster and Chure, 2006) at the Little Houston Quarry. U.S. quarter for scale. (D) Left humerus of Camarasaurus and femur of diplodocine(?) at the Little Houston Quarry, Brunton indicating north. 32 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 restricted to the layers above the channel, which is up to 20 m wide. Dinosaur material at the site is largely associated to articulated (figures 2C and 2D), with a sig- nificant number of isolated elements as well. Microver- tebrate material is mixed in with the same layers as the articulated dinosaur elements, often concentrated in two 1- to 10-cm-thick layers separated vertically by 15 to 30 cm within the interbedded mudstone and lami- nated siltstone above the channel sandstone. Dinosaur material in the quarry is abundant and densely concentrated, with up to 25% of material in ar- ticulation (figures 3A and 3B; for articulation percent comparison with other localities see Foster and others, 2018). Camarasaurus elements are particularly abun- dant, with sections of at least four adult individuals in articulation. MATERIAL AND METHODS Fossil material was collected from the Little Hous- A N B Little Houston Quarry Maps MAIN PIT Grid Squares = 1 m Pit black lines: excavation walls Mamma Pit approximately 70 m north of main pit Red: Allosaurus Green: Camarasuarus Light Purple: Diplodocinae Light Blue: Sauropoda indet. MAMMAL PIT Dark Blue: Dinosauria indet. Orange: Nanosaurus Tan: Tanycolagreus? Figure 3. Quarry maps of the Little Houston Quarry. (A) Map of main pit. (B) Map of mammal pit. Each map grid square = 1 m. 33 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 ton Quarry each summer continuously from 1991 to 2000 and again from 2004 to 2011, principally by the SDSM’s Museum of Geology but also by the MWC (Foster, 1992, 1993, 1996a, 1996b, 2001, 2018; Foster and Martin, 1994; Martin and Foster, 1998; Pagnac, 1998; Foster and Trujillo, 2000, 2018; Foster and others, 2018). The biota consists of at least 35 taxa, including four plants, five invertebrates, and 26 vertebrates (table 1). Foster (2001) assessed the relative abundances and taphonomy of taxa found through the 2000 field season, but the full biota has never been described or illustrated in detail. Specimens were compared to existing museum col- lections and published illustrations of other material. Theropod tooth terminology used in tooth descriptions incorporates terms of Hendrickx and others (2015) whereas that for mammals utilizes those of Kielan-Ja- worowska and others (2004). Cladistic analysis utilized Mesquite 3.0 and TNT 1.5. SYSTEMATIC PALEONTOLOGY PLANTAE Chlorophyta Charophyta Indet. Three charophyte oogonia have been found in the Little Houston Quarry over the years, but all were lost in the course of study due to unfortunate laboratory mishaps before they could be photographed. There are at least six genera of charophytes known from the Mor- rison Formation, and they have been reported at least from the Piedmont area of the Black Hills (South Dako- ta), in addition to the unidentified taxa reported from Little Houston here (Schudack and others, 1998). Polypodiopsida Equisetales Equisetum sp. One plant specimen (JRF 95153) has been identified as a stem of a relatively large horsetail, probably Equise- tum (figure 4A). Horsetail fossils are relatively common in the Morrison Formation, both in Wyoming and the Colorado Plateau (Tidwell and others, 1998, 2006; Ash Table 1. Biota list of taxa known from the Little Houston Quarry, Morrison Formation, Crook County, Wyoming. PLANTAE Chlorophyta Charophyta indet. Polypodiopsida Equisetales Equisetum sp. Polysporangiophytes Tracheophytes Pteridospermatophyta? Gymnosperma? Indet. METAZOA Mollusca Gastropoda Amplovalvata sp. Bivalvia Unionidae indet. (“Unio” stewardi?) Unionida indet., new genus? Arthropoda Malacostraca? Crayfish? Diplostraca “conchostracans” Chordata Osteichthyes Actinopterygii Actinopterygii indet. Scale type A Actinopterygii indet. Scale type B Actinopterygii indet. Scale type C Sarcopterygii Dipnoi Ceratodus fossanovum Amphibia Anura indet. Caudata indet. Reptilia Testudinata Dinochelys whitei Glyptops plicatulus Testudinata indet. Rhynchocephalia Opisthias? Squamata cf. Paramacellodus Archosauria Choristodera Cteniogenys antiquus Crocodylomorpha Crocodyliformes Atoposauridae Theriosuchus morrisonensis Goniopholididae? indet. Crocodyliformes indet. Archosauria indet. Pterosauria Pterosauria indet. Dinosauria Saurischia Theropoda Tetanurae Allosauroidea Allosaurus jimmadseni Coelurosauria Tanycolagreus? Dromaeosauridae indet. Theropoda Indet. Tooth type A (cf. Richardoestesia?) Tooth type B Tooth type C Tooth type D (abelisauroid?) Tooth type E Sauropoda Diplodocidae Diplodocinae indet. Macronaria Camarasauridae Camarasaurus sp. Ornithischia Thyreophora Stegosauridae indet. Neornithischia Nanosaurus agilis Mammalia Docodonta Docodon cf. apoxys Multituberculata Allodontidae indet. Dryolestida Dryolestidae Amblotherium megistodon n. sp. 34 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 and Tidwell, 1998), and this fossil represents one of the larger specimens reported from the unit. Polysporangiophytes Tracheophytes Pteridospermatophyta? One specimen (JRF 9411) represents a small, well preserved seed less than 2 mm in diameter (figure 4B). It appears to consist of a complete seed with ribbed in- tegument, possibly from an indeterminate seed fern (C. Gee, University of Bonn, written communication, 2018). Gymnospermae? indet. Carbonized, roughly rectangular (and sometimes relatively thick) plant fragments (represented by SDSM 25305, figure 4C) are the most abundant plant material in the deposit. It is unclear what element or taxon these represent, although one hypothesis is that they are par- tial cone or seed scales of conifers (e.g., Tidwell, 1998; Eckenwalder, 2009) or, alternatively, cycad leaf-scales such as those of Cycadolepis (e.g., Tidwell and others, 1998). METAZOA Mollusca Gastropoda Amplovalvata sp. Several gastropods have been found in the Little Houston Quarry, and at least one of these (JRF 9359; figure 5A) appears to belong to the genus Amplovalvata (Yen, 1952; Evanoff and others, 1998), although it is not well preserved enough to identify to species. Bivalvia Unionida Unionidae indet. Specimens of unionids are relatively abundant in the deposit, and most are preserved as impressions in the siltstone matrix; however, one specimen from the underlying sandstone preserves the shell nearly intact. None of these specimens is well preserved enough to be certain of their identifications within Unionidae, but one large (~8 cm) specimen (figure 5B) and the one preserving shell material (figures 5C and 5D) may rep- resent “Unio” stewardi or “U.” felchi, and either “Unio” sp. or possibly Vetulonaia, respectively (Branson, 1935; Evanoff and others, 1998). Unionida indet., new genus? Most abundant in the Little Houston Quarry, how- ever, is an unusual unionoid consisting of very elongate shell valves and often preserved as impressions of ar- ticulated but open shells (figures 5E and 5F). Unionids with this degree of relative elongation (up to 4.6:1) have Figure 4. Representative plant material from the Little Hous- ton Quarry. (A) Horsetail stem Equisetum sp., JRF 95153, scale bar = 1 cm. (B) Seed of possible pteridospermatophyte (seed fern), JRF 9411, scale bar = 1 mm. (C) Carbonized impression of possible cone scale or cycadophyte leaf-scale, SDSM 25305, scale bar = 1 cm. 35 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 not previously been reported from the Morrison For- mation (Branson, 1935; Yen, 1952; Evanoff and others, 1998; Good, 2004). Among modern unionoids such elongate shell dimensions are known in several genera of the families Unionidae and Mycetopodidae (Ander- son, 2014), and these taxa live in a range of freshwater environmental settings, including in muds and sands or firm grounds of rivers or oxygenated to dysoxic lake beds. Further identification of this taxon in the Little Houston Quarry will require additional material. Arthropoda Malacostraca? One small specimen (MWC 5640) appears to be the incomplete posterior walking leg of a small crayfish or other malacostracan (figure 6). The specimen is less than 1 cm long and appears to consist of three to five Figure 5. Representative Little Houston Quarry Mollusca. (A) Impression of gastropod Amplo- valvata sp., JRF 9359, scale bar = 1 cm. (B) Impression of inde- terminate unionoid, scale bar = 5 cm. (C and D) Indeterminate unionoid shell, scale bars = 1 cm. (E) Impressions of indeterminate elongate unionoids, scale bar = 5 cm. (F) Overview of same slab as in (E), showing additional speci- mens, scale bar in cm. (B to F) all SDSM unnumbered. 36 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 podomeres, including a spinose dactylus, the propodus, and carpus, but the nature of the more proximal ele- ments is unclear. The leg is similar in size to an isolat- ed, more anterior walking appendage from the Fruita Paleontological Area in western Colorado illustrated by Hasiotis and others (1998); the limbs of a nearly com- plete crayfish from the Mygatt-Moore Quarry in west- ern Colorado, illustrated by Foster and others (2018), are too poorly preserved to compare. Diplostraca Several diplostracans (previously referred to as “con- chostracans;” Martin and Davis, 2001) have been found in the quarry (e.g., JRF 9521, not figured), but they are very rare. Previous studies of Morrison diplostracans indicate that there are at least four taxa, mostly in Colo- rado and Utah (Lucas and Kirkland, 1998). Chordata Osteichthyes Actinopterygii indet. Actinopterygian fish are represented by many ele- ments from the Little Houston Quarry, including nu- merous upper and lower jaw fragments (figure 7), and three types of scales similar to those illustrated from other sites by Kirkland (1998) and Foster and Heckert (2011). The scales include abundant, tiny ganoid scales (figures 7A and 7B), whereas the jaw elements include a diverse sample of upper and lower elements, with al- most no two the same (figures 7C to 7I). One fish spec- imen appeared in the field to be an operculum and pec- toral fin of a large amioid, but this specimen has not yet been prepared. Dipnoi Ceratodus fossanovum There are a number of species of lungfish known from the Morrison Formation, including Ceratodus fossanovum, Ceratodus robustus, and Potamocerato- dus guentheri (Kirkland, 1987, 1998; Pardo and others, 2010), each best distinguished on tooth plate morphol- ogy. Lungfish are known from several specimens at the Little Houston Quarry, including a left dentary and tooth plate (figure 7J), along with several isolated tooth plates. The tooth plates of most of these specimens, in- cluding that of the left lower jaw (MWC 6505), are most similar to Ceratodus fossanovum in having a more ob- tuse inner angle, lower ridges, and a lingual crushing surface; C. fossanovum is also known from Quarry 9 at Como Bluff and from Ninemile Hill, Wyoming (Kirk- land, 1998; Trujillo, 1999). Amphibia Anura indet. Frogs are represented by a single distal half of a humerus with the preserved shaft and trochlea (figure 8A); this specimen is just over 6 mm long and is the only evidence of frogs from the Morrison Formation north of Como Bluff, Wyoming. The Morrison contains a pelobatid frog and the discoglossid Enneabatrachus at Quarry 9 and the pipoid Rhadinosteus at Dinosaur National Monument (Evans and Milner, 1993; Henrici, 1998), although this partial humerus cannot be identi- fied more precisely. Caudata indet. Salamanders are known from just a handful of Figure 6. Crayfish walking leg from Little Houston Quarry, MWC 5640, scale bar = 1 cm. 37 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 Figure 7. Representative Little Houston Quarry osteichthyan fish fossils. (A) Ganoid scale, JRF 9470. (B) Ganoid scale, JRF 9588. (C) Maxilla(?) fragment with teeth, JRF 95232. (D) Maxilla(?) fragment with teeth, JRF 9529. (E) Maxilla(?) fragment, JRF 9572. (F) Dentary(?) fragment with teeth, JRF 95138. (G) Maxilla(?) fragment, SDSM specimen. (H) Dentary(?) frag- ment with teeth, MWC 5762. (I) Jaw fragment with two teeth, MWC 5779. (J) Lungfish Ceratodus fossanovum, left dentary and tooth plate, MWC 6505. Scale bars A and B = 2 mm; all other scale bars = 1 cm. 38 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 strongly amphicoelous vertebrae with dorsoventrally elongate diapophyses (figures 8B to 8G). Most Morri- son salamander vertebrae are fairly small, but a few are somewhat larger (Evans and Milner, 1993), suggesting at least two different-sized groups. The specimen il- lustrated here is of the larger size class (centra ~5 mm length). Some Morrison salamanders such as Iridotri- ton (Evans and others, 2005) are significantly smaller than the taxon illustrated here from the Little Houston Quarry. Reptilia Testudinata Dinochelys whitei The relatively smooth-shelled turtle Dinochelys (Gaffney, 1979) is the most abundant turtle in the de- posit, outnumbering Glyptops significantly. Many pre- served pleural elements are small and preserved intact and unbroken with unfused sutures, suggesting many of the individuals preserved were juveniles (figures 9A to 9C). At least one shell fragment was found with the lat- erally radiating dorsal ridges typical of young juveniles (Gaffney, 1979). Glyptops ornatus The turtle Glyptops is known from a number of shell fragments exhibiting strong sculpturing (Marsh, 1890b; Hay, 1908; figures 9D to 9E); it is far less abundant in the Little Houston Quarry than Dinochelys. Testudinata indet. Many limb and some axial elements of indetermi- nate turtles are known from the quarry, including hu- meri, femora, a tibia, and sacral vertebrae (figures 9F to 9I). These cannot be identified to genus but indicate the abundance of turtles generally in the deposit. Rhynchocephalia Opisthias? The sphenodontian Opisthias? is represented by several small dentary fragments, a palatine, and an in- determinate jaw fragment (figures 10A to 10F). The two apparent dentary fragments illustrated here (figures 10C to 10F) are approximately the same size and the first of these (figures 10C and 10D) may be more frag- mentary or may represent a morphotype with relatively larger teeth. Rhynchocephalians are numerous in the Morrison Formation (Foster, 2003) though not, as far as we currently recognize, particularly diverse, with three genera currently represented: Opisthias, Theretairus, and the large, herbivorous Eilenodon (Gilmore, 1910; Simpson, 1926; Rasmussen and Callison, 1981; Jones and others, 2018). Recent analyses suggest there may be a previously hidden diversity of rhynchocephalians in the Morrison Formation (DeMar and others, 2018), although the material from the Little Houston Quarry is not complete enough to identify further. Figure 8. Little Houston Quarry Amphibia. (A) Frog humer- us, distal half in anterior view, JRF 9545. (B to G) Caudata (salamander) vertebra in (B) anterior, (C) posterior, (D) left lateral, (E) right lateral, (F) dorsal, and (G) ventral views. All scale bars = 5 mm. 39 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 Squamata cf. Paramacellodus Lizards are represented by a single tiny dentary just 6 mm long. It preserves 11 short, blunt teeth suggestive of a scincomorph and is likely a paramacellodid (figure 10G). The scincomorphs of the Morrison Formation include Paramacellodus, Saurillodon, and Schillerosau- rus (Prothero and Estes, 1980; Evans and Chure, 1998, 1999). The Little Houston Quarry jaw is not as short and deep as the dentary in Saurillodon (Broschinski, 2000) nor apparently as slender (dorsoventrally shallow) as Schillerosaurus, but it is similar to several specimens of Paramacellodus from Dinosaur National Monument Figure 9. Representative Little Houston Quarry turtles. (A) Dinochelys pleural, MWC 5780. (B) Dinochelys pleural, SDSM specimen. (C) Dinochelys pleural, SDSM specimen. (D) Glyptops pleural fragment, SDSM specimen. (E) Glyptops pleural fragment, SDSM 25343. (F) Testudinata indet., right humerus, MWC 5783. (G) Testudinata indet., left femur, SDSM 25246. (H) Testudinata indet., tibia(?), JRF 9528. (I) Testudinata indet., sacral vertebra, MWC 5865. All scale bars = 1 cm. 40 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 Figure 10. Representative Little Houston Quarry Lepidosauria. (A to F) Opisthias?, Rhyncocephalia. (A) Left palatine in lat- eral view, MWC specimen. (B) Indeterminate jaw fragment in lateral view, MWC specimen. (C and D) Dentary(?) fragment in (C) labial and (D) lingual views, EBG 9833. (E and F) Right dentary fragment (MWC specimen) in (E) labial and (F) lingual views. (G) Small cf. Paramacellodus (Scincomorpha, Squamata) right dentary in labial view, JRF 95102. Scale bars = 5 mm. 41 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 (Evans and Chure, 1998) in its proportions and overall structure. Choristodera Cteniogenys antiquus Choristoderes are relatively abundant in the de- posit, being represented by numerous isolated ver- tebrae, and several upper and lower jaw fragments (figure 11). Cteniogenys was a small (~25 cm long) semiaquatic choristodere common in the Late Jurassic of North America and Europe (Gilmore, 1928; Evans, 1990). It appears to have been significantly more abun- dant in the eastern and northern parts of the Morrison Formation than it was in what is now the Colorado Plateau region (Chure and Evans, 1998; Foster and Trujillo, 2000). Crocodylomorpha Crocodyliformes Atoposauridae Theriosuchus morrisonensis This newly named species of atoposaurid crocody- liform (Foster, 2018) was based on a lower mandible found in the Little Houston Quarry in 2004 (figures 12A to 12C). The jaw indicates an atoposaurid simi- lar to Theriosuchus pusillus and Knoetschkesuchus was present in at least the northern region of the Morrison Formation. Goniopholididae? indet. Several isolated teeth at the site appear to belong to relatively large crocodyliforms, probably goniopho- lidids (figure 12D). The form and size of the teeth is essentially indistinguishable from goniopholidids from the Morrison Formation, such as Eutretauranosuchus and Amphicotylus (Mook, 1967; Smith and others, 2010; Allen, 2012). Crocodyliformes indet. Relatively abundant and not particularly large croc- odyliform osteoderms from the quarry could be those of goniopholidids, although these are not dorsal armor with the rectangular plates and anterior projections typ- ical of that family. These are squarish to almost oval in shape (figures 12E to 12F) and could conceivably be- long to any of several families of crocodyliforms. Archosauria indet. One tiny premaxilla appears to belong to an inde- terminate small archosauromorph (figure 12G). This small specimen has 5 to 6 conical teeth, a tall nasal pro- cess, a thick maxillary process, and is anteroposteriorly relatively short. Pterosauria Pterosauria indet. Pterosaurs are represented by a single, elongate tooth with a tall conical and slightly recurved crown, a long root, and an oval to slightly laterally compressed cross section (MWC 5809; figures 12H to 12I). This is a general form typical of some pterosaurs (Wellnhofer, 1991; Witton, 2013), and it is rather similar in over- all appearance to an anterior dentary tooth from the Breakfast Bench facies at Como Bluff described by Mc- Lain and Bakker (2017). Isolated pterosaur teeth are also preserved at Quarry 9 at Como Bluff (Carrano and Velez-Juarbe, 2006). Dinosauria Saurischia Theropoda Tetanurae Allosauroidea Allosaurus jimmadseni A juvenile Allosaurus partial skeleton from Little Houston Quarry (figure 2C) was described and illus- trated by Foster and Chure (2006) and was referred to A. jimmadseni by Chure and Loewen (2020). This spec- imen (SDSM 30510) demonstrated the extreme elonga- tion of the hindlimb relative to ilium length in juveniles of the genus compared with adults. It is also one of the more complete associated skeletons of a very young individual of the genus yet reported, consisting of cer- vicals, a dorsal, a sacral, both ilia, caudals, an ischium, 42 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 Figure 11. Representative Little Houston Quarry Cteniogenys (Choristodera). (A) Left maxilla in labial view, SDSM speci- men. (B and C) Right dentary fragment, MWC 6504, in (B) lingual view and fragment with well-preserved teeth (missing from (B) in (C) labial view. (D) Dentary fragment, JRF 95216. (E) Vertebra in dorsal view, SDSM specimen. (F) Dentary with teeth, small individual, JRF 95100. Scale bars = 1 cm, except E = 5 mm. 43 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 Figure 12. Representative Little Houston Quarry Crocodyliformes, Pterosauria, and Archosauromorpha indet. (A to C) Left mandible of Theriosuchus morrisonensis, MWC 5625, in (A) labial, (B) lingual, and (C) occlusal views. (D) Tooth of Goniop- holididae(?), SDSM 25337. (E) Osteoderm of Crocodyliformes indet., JRF 9571. (F) Osteoderm of Crocodyliformes indet., JRF 95211. (G) Archosauromorpha indet., premaxilla with teeth in lingual(?) view, JRF 95208. (H and I) Tooth of Pterosauria indet., MWC 5809; tooth tip in H) and base of crown plus root in I). Scale bars: A to C = 5 cm; D to F and H to I = 1 cm; G = 5 mm. 44 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 femur, tibia, metatarsals, and manual and pedal phalan- ges and unguals (Foster and Chure, 2006). A partial skeleton of an adult Allosaurus was also collected from the main pit (figure 3A), consisting of posterior dorsal vertebrae, a sacrum and both ilia, ante- rior caudal vertebrae, and a femur; preparation of this specimen is still being completed. Several teeth assigned to Allosaurus are also known from the quarry (figures 13K and 13L). These are relatively large teeth (~19 to 27 mm crown height) with denticles that are neither as coarse as in Torvosaurus nor as fine as in Ceratosaurus and with a distinctive cross-sectional shape similar to Allosaurus (Madsen, 1976; Madsen and Welles, 2000; Bakker and Bir, 2004). Other elements representing the adult Allosaurus from the quarry include a quadrate, premaxilla (Foster and Martin, 1994), dentary frag- ment, and dorsal and caudal vertebrae. Coelurosauria Maniraptora Tanycolagreus? A single right metatarsal II, collected from the mammal pit at the Little Houston Quarry, appears to belong to a small theropod (figures 13A and 13B). The metatarsal is too elongate to belong to Allosaurus (even a juvenile), Ceratosaurus, or Torvosaurus and is too ro- bust to be Coelurus (Madsen, 1976; Britt, 1991; Madsen and Welles, 2000; Carpenter and others, 2005a) and too large to be Ornitholestes or Koparion (assuming the lat- ter was as small as its lone tooth suggests). However, this specimen is essentially indistinguishable in propor- tions and articular end shapes from the metatarsals of Tanycolagreus (Carpenter and others, 2005b). The pes of Stokesosaurus and Marshosaurus is unknown in both. The Little Houston metatarsal is here tentatively identified as Tanycolagreus?, possibly the first occurrence of the tax- on north of Bone Cabin Quarry in southern Wyoming. Dromaeosauridae indet. A single isolated tooth from the quarry (figures 13E to 13G) is small, short, recurved, and laterally com- pressed (10.8 mm crown height), with strong serrations on the distal carina (4/mm) and only small indistinct serrations on the mesial carina. The distal serrations are slightly hooked apically, and in most of these characters the tooth is similar to those of Dromaeosaurus, Sauror- nitholestes, and Sinornithosaurus among dromaeosau- rids (Currie and others, 1990; Farlow and others, 1991; Fiorillo and Currie, 1994; Xu and Wu, 2001; Larson and Currie, 2013). It is a relatively large tooth at nearly 11 mm, with fine serrations on the distal carina. The tooth dimensions and denticle characteristics are similar to those of possible dromaeosaurid tooth morphotypes 5 and 6 reported from the Middle-Late Jurassic Shishugou Formation of China (Han and others, 2011). Overall tooth shape is also similar to teeth from Guimarota (Late Jurassic of Portugal) referred to Compsognathus (Zinke, 1998), although overall size and the distal den- ticles are both larger in the Little Houston specimen. Hendrickx and Mateus (2014) referred a similar tooth from the Late Jurassic of Lourinhã, Portugal, to Richar- doestesia, although the Little Houston tooth is approx- imately twice as large and has much larger denticles on the distal carina. The tooth is less strongly recurved than the Morrison troodontid Hesperornithoides (Hart- man and others, 2019) and less labiolingually bulbous than the troodontid Koparion (Chure, 1994). Reports of dromaeosaurid-like teeth from the Mor- rison Formation have been rare, with only two teeth illustrated, from the Dry Mesa Quarry in western Col- orado and the Warm Springs Ranch site in northern Wyoming (Britt, 1991; Ikejiri and others, 2006). The occurrence of dromaeosaurid (or at least dromaeosau- rid-like) teeth in at least three deposits in the Morri- son Formation, plus a number of dromaeosaurid teeth in the Late Jurassic of Portugal, Spain, Germany, Ethi- opia, and China (Zinke, 1998; Rauhut, 2000; Van Der Lubbe and others, 2009; Han and others, 2011; Hall and Goodwin, 2011), suggests that this family was rare but certainly present in many areas of the globe during the Late Jurassic. In the Morrison Formation, isolated, par- tial bones of possible dromaeosaurs were reported by Jensen and Padian (1989), but those are the only non- tooth evidence of the family in the formation. That no well-preserved skeletons of dromaeosaurids have been reported yet from the Late Jurassic may be indicative of their rareness at the time but may more likely be a result of taphonomic bias against smaller, more delicate material. 45 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 Figure 13. Representative Little Houston Quarry Theropoda (Dinosauria). (A and B) Right metatarsal II of Tanycolagreus?, JRF 95215, in (A) medial and (B) anterior views. (C) Tooth of theropod Tooth Type A (cf. Richardoestesia?), JRF 95222, and (D) in close-up showing serrations. (E to G) Tooth of Dromaeosauridae indet., JRF 95188, in (E) lingual(?), (F) labial(?), and (G) in close-up view of serrations. (H) Tooth of theropod Tooth Type B, MWC specimen. (I and J) Tooth of theropod Tooth Type C in (I) labial and (J) lingual views, JRF 9739. (K and L) Teeth of Allosaurus, SDSM specimen and JRF 9337. Scale bars: A and B = 10 cm; C, E, F, and H to J = 5 mm; D = 2 mm; G = 1 mm; K and L = 1 cm. 46 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 Despite the fragmentary evidence so far, it appears reasonable to conclude that dromaeosaurids were pres- ent in the Morrison Formation and that we might ex- pect to find more complete elements in the future. Theropoda indet. Tooth Type A (cf. Richardoestesia?) A small (4.1 mm crown height) and laterally com- pressed tooth (figures 13C to 13D) differs from the dromaeosaurid tooth type described above in having a relatively taller crown, in being less recurved, and in having finer serrations on the distal carina (8/mm) that are shorter with more rectangular and blunt apical pro- files. In these characteristics, the tooth type is roughly similar to many teeth assigned to Richardoestesia (Cur- rie and others, 1990), a taxon which has been identi- fied from the Late Jurassic of Portugal (Rauhut, 2000; Mateus, 2006; Malafaia and others, 2017). Although the Little Houston Quarry tooth is similar to some il- lustrated teeth of Cretaceous Richardoestesia in being somewhat recurved (Currie and others, 1990), a few Cretaceous and Jurassic specimens are relatively tall and less recurved (see figure 6 in Zinke, 1998; see figure 11.9 in Rauhut, 2000; Longrich, 2008). Larson and Cur- rie (2013) demonstrated the difficulties, in many cases, of distinguishing species of Richardoestesia and other small Cretaceous theropod taxa, based on teeth, and this indirectly implies there may be difficulty in refer- ring isolated teeth from other times or geographical ar- eas to the genus. Whatever taxon these possible cf. Rich- ardoestesia teeth from the Morrison and elsewhere in the Late Jurassic represent, it is clear that the Morrison and Guimarota faunas, for example, were more diverse in small theropod taxa that was previously apparent and that they likely shared closely related or congeneric taxa with Richardoestesia-like teeth. Tooth Type B Another isolated small theropod tooth (figure 13H) from the quarry is roughly similar to Tooth Type A above but is less laterally compressed and the nature of the serrations is unclear. Crown height for the speci- men is 5.0 mm. In some general ways this tooth appears similar to those of Coelurus (Marsh, 1896) and Ornitho- lestes (Carpenter and others, 2005a) and especially to an unidentified theropod tooth type from Guimarota, Portugal (see figures 8A to 8D in Zinke, 1998). Tooth Type C Another tooth from the quarry appears to be a small anterior theropod tooth (figures 13I to 13J) with a wear facet and the serrated mesial carina curving distal-lin- gually; this tooth type may belong to a young Allosau- rus. It is 5.7 mm in crown height with 3.5 denticles per millimeter. Tooth Type D (Abelisauroid?) A somewhat larger theropod tooth type (11 to 30 mm crown height, as preserved) from the quarry is the most unusual and consists of labiolingually thin, unre- curved teeth with slightly constricted crown bases and relatively distally tall serrations with very elongate, ba- sally oriented interdenticular sulci. The first representa- tive of these teeth (figures 14A to 14E) is approximately 11 mm in crown height; in labial or lingual view the me- sial and distal carinae both curve symmetrically toward the apex so that the tooth is unrecurved, except for a very slight posterior(?) curvature at the tip. The tooth is labiolingually thin compared to its mesiodistal length and curves slightly lingually toward the apex. The tooth is serrated from apex to crown base along both mesial and distal carinae, and the lower portion of the mesi- al carina has approximately 5 denticles per millimeter. Each denticle curves slightly apically at its distal end (figure 14E). The second representative of Tooth Type D is simi- lar in overall shape but the apex is not preserved (figure 14F). It is larger than the first and was probably about 30 mm long when complete. The root of this tooth is missing, suggesting it is a shed tooth, and in lingual view the crown appears to have been very slightly con- stricted at its base, as in the first tooth described above. Also in lingual view, the mesial and distal carinae both curve symmetrically toward the apex so that the tooth is unrecurved. Despite being partially in matrix, the tooth can be seen in mesial or distal view to be strong- ly labiolingually compressed relative to its basal length. The serrations are more elongate proximodistally than 47 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 in most other theropod teeth from the Morrison For- mation and the interdenticular sulci are long and dis- tinct. On this larger tooth there are approximately two serration denticles per millimeter; each denticle curves slightly apically at its distal end. The enamel on the lin- gual surface is relatively smooth and neither concave Figure 14. Unusual Little Houston Quarry Theropoda (Dinosauria) teeth. (A to E) JRF 94130. Tooth of theropod Tooth Type D in (A) labial view, (B) distal view, (C) lingual view, and (D) mesial view. JRF 94130 is approximately 11 mm in height. (E) Close-up of denticles of distal carina near base of crown, JRF 94130. (F) Second specimen of theropod Tooth Type D, scale bar = 1 cm. (G) Tooth of theropod Tooth Type E, EBG 9830, in lingual view and (H) with close-up of denticles as marked by white box in G. Scale bars: G = 1 cm; H = 5 mm. (Photos A to E courtesy of National Park Service.) 48 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 nor convex, but rather appears to be flat from a subtle central ridge out to the carinae. These teeth (figures 14A to 14F) share some dis- tinct similarities to the procumbent anterior dentary or premaxillary teeth of the noasaurid abelisauroid Ma- siakasaurus from the Cretaceous of Madagascar (Car- rano and others, 2002, figures 5A to 5C of FMNH PR 2180) in being thin, not distally recurved, and in having pinched crown bases in labial or lingual view. The Little Houston Quarry teeth are not as thick nor as lingual- ly curved toward the apex as in FMNH PR 2180, how- ever, and are also similar to FMNH PR 2182 (Carrano and others, 2002, figure 5E), although they are not re- curved as in that Masiakasaurus specimen. These sim- ilarities suggest that the Type D Morrison specimens (figures 14A to 14F) may represent the anterior teeth of an unknown small- to medium-sized abelisauroid or ceratosaurian. In the general characteristics of the ser- rations and overall shape, Type D teeth are similar to other Late Jurassic teeth referred to abelisaurids from Lourinhã, Portugal (Hendrickx and Mateus, 2014) and to a possible carcharodontosaurid from the Tendaguru Formation of Tanzania (Rauhut, 2011). In overall shape the Little Houston specimens are also similar to lateral dentary teeth from a very small theropod jaw from Gui- marota in Portugal (Zinke and Rauhut, 1994). No teeth of this morphology have previously been reported from the Morrison Formation, and it is un- clear if the teeth represent a previously unknown tax- on or a currently known taxon for which there is no tooth material. Among the Morrison theropods for which known teeth do not match Tooth Type D are: Allosaurus, Torvosaurus, Ceratosaurus, Marshosaurus, Ornitholestes, Coelurus, Koparion, Hesperornithoides, and Tanycolagreus. Taxa without teeth or with poorly known teeth include Saurophaganax, an unidentified abelisauroid(?) (formerly “Elaphrosaurus”), Fosterove- nator, and Stokesosaurus. If the similarities of the Type D teeth to those of anterior teeth of Masiakasaurus are significant, and if the teeth belong to a known taxon with no or poor tooth representation, the best candi- dates might be the unidentified abelisauroid or possibly Fosterovenator. Finding this tooth type with associated skull material will be key to determining its affinities. Tooth Type E A lone tooth somewhat similar to Type D is also known; it is thicker, shorter, and lingually more convex (figures 14G and 14H), though it possesses similarly elongate serration denticles (figure 14C). These serra- tions are coarser than in Type D, too, however (1.75/ mm); the denticles appear to be angled apically and to have slightly enlarged rather than apically curved distal ends, both unlike Type D. The crown height is 25 mm. This tooth type appears to be that of an anterior tooth, and the apparently distally enlarged denticles are similar to some referred teeth of abelisaurids (Hendrickx and Mateus, 2014), but beyond that it is difficult to identify. Sauropoda Diplodocidae Diplodocinae indet. Diplodocine sauropods are represented at the Lit- tle Houston Quarry by only rare elements including a pubis and at least one complete, slender femur (figures 2D and 3A). The pubis is slender and has an enlarged ambiens process as with diplodocines such as Diplod- ocus and Barosaurus (Hatcher, 1901; McIntosh, 1990; Ostrom and McIntosh, 1999). Macronaria Camarasauridae Camarasaurus sp. Camarasaurus is represented by at least six or possi- bly seven individuals, including four articulated verte- bral series: a set of anterior to mid caudals and a set of posterior dorsals and most of a tail from the mammal pit (both in figure 3B); and a partial mid-tail and a near- ly complete vertebral column from anterior cervicals to the tip of the tail from the main pit (both in figure 3A). In addition to these four individuals, there is a partial hind foot of a juvenile, a partial skull of a large individu- al found near (but probably not belonging to) the nearly complete vertebral column (figure 3A), and a hatchling to very young juvenile represented by a tiny tooth. The Camarasaurus material from the Little Houston Quar- ry cannot be assigned to one species (Pagnac, 1998), in part because the dorsal vertebrae of the most complete 49 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 specimen do not clearly exhibit diagnostic features due to post-depositional crushing. Most anterior caudal vertebrae, however, appear to have only mildly expand- ed neural spines, suggesting possible affinity to C. lentus (Ikejiri, 2005). The skull (SDSM 114501) is relatively large and is flattened to some degree with a number of teeth dis- placed from their alveoli and the premaxillae, for ex- ample, displaced dorsoventrally relative to each other (figure 15A). The skull was found underneath two sau- ropod ribs and near several camarasaurid metacarpals, several meters away from the end of the neck of the most complete Camarasaurus vertebral column in the quarry (figures 15B and 3A). The skull appears to have been too large to go with the neck and skeleton, howev- er. The associated juvenile hind foot consists of the left metatarsals I, IV, and V, plus two unguals, and a phalanx (figure 15C; Foster, 1996a). A 5 mm-long tooth crown with partial root (JRF 9584) appears to belong to a very young camarasaurid and has an apical wear facet sug- gesting some use (figures 15D and 15E). This tooth has the general shape of most adult camarasaurid teeth (Os- trom and McIntosh, 1999), although the enamel surface appears to be smoother. Ornithischia Thyreophora Stegosauridae indet. A thin, plate-like bone with surficial grooves appears to be the dermal plate of a stegosaur (SDSM 25300; figure 16). The plates of Stegosaurus and Hesperosaurus are gen- erally similar in structure, although their shapes differ somewhat, with those of the latter often lower and more oval-shaped (Carpenter and others, 2001; Maidment and others, 2015). The Little Houston Quarry specimen here is too incomplete to identify with one or the other genus, but its overall morphology appears to be that of some type of stegosaurian plate. Hesperosaurus has re- cently been reported at a number of northern localities in the Morrison Formation, appearing to be relatively more abundant there compared with the possibly more southern Stegosaurus (Maidment and others, 2018), and raising the possibility that SDSM 25300 may be Hespero- saurus, although there is no way to confirm this yet. Neornithischia Nanosaurus agilis Small neornithischians are represented by relative- ly abundant material including a dentary with 13 teeth (Peirce, 2006; Carpenter and Galton, 2018; figure 16A), isolated anterior and lateral teeth (figures 17B and 17C), some vertebrate (figure 17D), a humerus (figure 17E), a pubis (figure 17K), a tibia of an adult (figure 17J), and a number of femora ranging in length from just a few centimeters to approximately 20 cm (figures 17F to 17I). The teeth are entirely of the “Othnielosau- rus” type (Galton, 2007), and no “Drinker” type teeth (Bakker and others, 1990) have been found. Carpenter and Galton (2018) pointed out that both types of teeth have been found in the same jaw in some instances and synonymized both taxa with Nanosaurus agilis (Marsh, 1877; Galton, 1983). One unusual anterior tooth with root is preserved (figures 17L and 17M), though it has not been fully prepared yet. Mammalia Multituberculata Allodontidae indet. SDSM 26912 is a relatively large, partial right mul- tituberculate dentary with p4 and m1 from the main pit of the Little Houston Quarry (figure 18A). The speci- men was probably about 23 mm long when complete, with a p4 length of 2.6 mm. The coronoid process is in- tact, and the posterior part of the jaw consists of bone and an impression in matrix. The m1 is worn labially but appears to have had two rows of three cusps. The dentary anterior to the p4 is missing but is represented by an impression in the matrix for part of its length. The specimen was identified as Psalodon? marshi in its first description by Martin and Foster (1998); that species is also known from Quarry 9 at Como Bluff (Simpson, 1929). This specimen was the first mammal found at the Little Houston Quarry. SDSM 26912 differs from Ctenacodon serratus and C. scindens in the larger size of the p4, the larger over- all size of the jaw, the relatively smaller m1 (compared with p4), and the slightly greater ratio of the depth of the dentary below p4 to the dentary length (table 2; 50 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 Simpson, 1929). The specimen is similar to Zofiabaatar (Bakker and others, 1990) in the dentary length, the length of p4, and the dentary depth to length ratio, but it differs from that taxon in having: (1) an m1 relatively not as small (compared with p4), (2) an m1 with two rows of three cusps (as opposed to two of two in Zofia- baatar), and (3) a condyle not facing as much dorsally as that taxon (table 2; Carpenter, 1998). SDSM 26912 differs from Glirodon grandis in larger overall size and larger p4, in having a smaller m1 compared to p4, and Figure 15. Representative Little Houston Quarry Camarasaurus (Dinosauria, Sauropoda). (A) Skull in right lateral view, SDSM 114501, showing displaced teeth and offset of premaxilla. (B) Left lateral view of caudal vertebra, SDSM 35943, from mammal pit specimen. (C) Partial foot of juvenile individual including metatarsals I, IV, and V, phalanx, and two unguals, SDSM specimen. (D and E) Tooth of hatchling(?) individual in (D) labial view and (E) distal(?) view showing wear facet. Scale bars in A to C in cm; scale bars in D and E = 5 mm. 51 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 in having a less robust ramus (table 2; Engelmann and Callison, 1999). As in Ctenacodon, the post-coronoid portion of the ramus of SDSM 26912 is also relatively longer than in Glirodon. The specimen is similar to Psalodon? marshi in the structure of m1 and in having a large p4, but it differs from that taxon in having an m1 smaller relative to p4 and has a seemingly longer, lower dentary with a less convex ventral border in lateral view and apparently with a smaller incisor. SDSM 26912 appears not to fit well with P.? marshi, Ctenacodon, Glirodon, or Zofiabaatar and may in fact represent a separate as yet unidentified multitubercu- late taxon in the Morrison Formation. P.? marshi itself (e.g., USNM 2684) in fact may represent a taxon closer to Plagiaulax becklesii and may not be closely related to Ctenacodon. Docodonta Docodontidae Docodon cf. apoxys Several jaw fragments and isolated teeth of Docodon have been found since 1993 (Martin and Foster, 1998; Foster and others, 2006), when the first mammal speci- mens were uncovered. These specimens include at least three dentary fragments (Foster and others, 2006; fig- ure 18B), a maxilla fragment (figure 18F), a large canine (figure 18D), and some isolated molars. The molars of at least one of the specimens are of the type described for D. apoxys from Garden Park (Rougier and others, 2015) in having reduced molar size near the posterior end of the dentary, especially in the last molar (as indicated by alveolus size in the case of the Little Houston Quarry specimen). This specimen (SDSM 60480; figures 18B Figure 16. Dorsal(?) plate fragment of Stegosauridae indet. from the Little Houston Quarry, SDSM 25300. Scale bar = 5 cm. 52 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 Figure 17. Representative Little Houston Quarry Nanosaurus (Dinosauria, Neornithischia). (A) Right dentary with 13 teeth in labial view, MWC 5822. (B) Anterior tooth in lingual view, JRF 95220. (C) Lateral tooth in labial view, JRF 95148. (D) Caudal vertebra in posterior view, SDSM 30496. (E) Right humerus in medial view, SDSM 30502. (F) Tiny femur mid-shaft with partial fourth trochanter, JRF 9822. (G) Left femur in anterior view, SDSM 26913. (H) Complete left femur in medial view, SDSM 30494. (I) Complete left femur of adult in medial view, SDSM 30490. (J) Complete tibia in posterior view, MWC 5630. (K) Right pubis, SDSM 30503. (L and M) Anterior tooth in lingual view and close-up, JRF 95126. Scale bars: A, D, F, and L = 1 cm; B, C, and M = 5 mm; E and G to K = 5 cm. 53 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 Figure 18. Little Houston Quarry multituberculate and docodont mammals. (A) Partial right dentary with p4 and m1, in labial view, assigned to Allodontidae indet., SDSM 26912. Scale bar = 1 cm. (B to F) Docodon. (B) Partial left dentary of Doco- don cf. apoxys, SDSM 60480, in lingual view, with m2–5(?) and alveoli for m6 and m7. Scale bar = 5 mm. (C) Close-up labial view of molars m2–m5(?) of jaw in B (SDSM 60480). Scale bar = 1 mm. (D) Canine tooth in lingual(?) view, SDSM speci- men. Scale bar = 1 mm. (E) Jaw fragment with lower molar, incoming more distal molar(?), and some dentary bone, SDSM specimen. Molar length ~2 mm. (F) Left maxilla fragment with canine, MWC specimen, in lingual view. Scale bar = 5 mm. 54 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 and 18C) consists of a partial left dentary with m2–5(?) and alveoli for m6 and m7 of reduced size (especially m7). This specimen would be the first occurrence of D. apoxys outside of its type area in Garden Park, Col- orado. Docodon is well known from a number of sites in Wyoming (Quarry 9 and others) and eastern Colo- rado (Small and Marsh-Felch Quarries, Garden Park) (Simpson, 1928; Kielan-Jaworowska and others, 2004), although it is absent from the Morrison of the Colorado Plateau (Foster and others, 2006). Cladotheria Dryolestida Dryolestidae Amblotherium Amblotherium megistodon, sp. nov. Figure 19 LSID. urn:lsid:zoobank.org:pub:A69FB058-C18B- 4AAF-BC4B-EE68E3682561. Type Specimen SDSM 148545, left dentary preserved in labial view with p2–p4 and m1–m3 in place. Type Locality Little Houston Quarry (mammal pit), Crook Coun- ty, Wyoming (Foster and Martin, 1994; Foster, 2001). Type Horizon Morrison Formation undifferentiated; thin local Morrison section of only ~23 m (Mapel and Pillmore, 1963); thickness and intraformational correlation with other localities in Wyoming unknown. Etymology From Greek μεγíστ (megist) meaning “largest” + όδόυ (odon) meaning “tooth,” in reference to the much larger over- all size compared with other species of Amblotherium (A. gracile and A. pusillum), especially as reflected in the teeth. Diagnosis Amblotherium species with isometrically larger den- tary and teeth than other species of the genus (m3 up to 87% longer than in other species; 1.5 mm mesiodistal length compared with average of 0.80 mm in A. pusil- lum and A. gracile) and differing from other species of the genus in having roots of unequal size in m1 and m2 as well as more distal molars; other characters match generic diagnosis of Amblotherium. Description and Identification SDSM 148545 is a mostly complete left dentary with p2–p4 and m1–m3 (figure 19) and is a dryolestid, as indicated by the enlarged and bean-shaped mesial al- veolus and reduced, oval-shaped distal alveolus of m4. The dentary is 21.97 mm long as preserved and is miss- ing only the anterior end (incisors and full canine al- veoli not preserved), posterior tip, and upper coronoid process. The jaw is in a piece of matrix with the labial and occlusal surfaces exposed, and preparation has ex- posed the lingual sides of the preserved teeth. The six Table 2. Comparison of features of various species and specimens of jaws of multituberculate mammals from the Morrison Formation. Ctenacodon Psalodon? marshi Zofiabaatar pulcher Glirodon grandis SDSM 26912 Dentary Length 17.5 Incomplete 23 17.3 ~23.3 Length p4 1.65 3 2.6 1.9 2.6 Length p4:m1 1.4 1.43 1.98 1.5 1.72 Dentary depth at p4: Dentary length 0.192 Incomplete 0.257 0.297 0.235 m1 cusps 2 rows of 3 2 rows of 3 2 rows of 2 2 rows of 3 2 rows of 3 Dentary ramus deeper under coronoid No No Yes No No Dentary condyle facing Posteriorly Posteriorly Posterodorsally Posterodorsally Posteriorly References Simpson, 1928, 1929 Simpson, 1929 Bakker and others, 1990; Carpenter, 1998; Kielan-Jaworowska and others, 2004 Engelmann and Callison, 1999 This report 55 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 preserved teeth include p2–p4 and m1–m3, and the al- veolus for p1 is exposed too (figure 19). The alveoli for m5 and m6 are poorly preserved due to partial crush- ing and are positioned partly lingual to the base of the coronoid process, suggesting the individual is a juvenile (Martin, 1999, 2000). The cusps of the molars are sharp and slender (fig- ure 19C). The molars differ from those of Laolestes in Figure 19. Dryolestid mammal Amblotherium megistodon n. sp., SDSM 148545, holotype, left dentary, Little Houston Quar- ry. (A) Labial view showing p2–p4 and m1–m3. Total length of specimen as preserved is 21.97 mm. (B) Occlusal view showing teeth and alveoli (as labelled) from partial canine(?) alveolus to m6(?). (C) Close-up view of p3–m3 in labial view with cusps labelled. Length of m3 = 1.5 mm. Protoconid cusp heights (m1 and m2) reconstructed from field photos. (D) Tracing of photo of m3 in occlusal view showing features and proportions. Abbreviations for C and D: med = metaconid, pad = paraconid, prd = protoconid, p4 = premolar 4, tc = talonid cusp, tad = talonid, trd = trigonid. 56 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 not having a bifid metaconid, in not having the paraco- nid and talonid cusp positioned internal to the metaco- nid (figures 19B and 19D), and in having an essentially erect (not slightly procumbent) paraconid. The premo- lars lack the anterior accessory cusp characteristic of Dryolestes (other than D. leirensis), and the molars differ from those of Dryolestes in having a more erect rather than procumbent paraconid (m3 cusp reconstruction in figure 19C based on pre-damage preliminary images). The jaw matches Amblotherium in having: (1) a slender ramus, (2) molars with an erect paraconid close to the height of the metaconid, (3) molars with a weak external cingulum, and (4) a coronoid with a low-sloping ante- rior edge (Simpson, 1928, 1929; Kielan-Jaworowska and others, 2004). The slenderness of the ramus in SDSM 148545 is in- dicated by the ratio of the maximum jaw depth to the reconstructed jaw length, and the ratio is similar to Am- blotherium (SDSM 148545 only 4.5% lower than other species of Amblotherium; see table 3). This dentary slen- derness ratio also differentiates the Little Houston den- tary from Dryolestes and Laolestes (ratio 19.7% lower than in Dryolestes; ratio 24.3% lower than in Laolestes). Molar size differs relative to jaw depth in SDSM 148545 and Amblotherium versus Dryolestes and Laolestes, with the latter genera having relatively lower crowned mo- lars. The ratio of the crown height of m3 to the depth of the dentary below m3 ranges from means of 0.366 and 0.362 for Dryolestes and Laolestes, respectively, to 0.707 and 0.657 for Amblotherium and SDSM 148545 (table 3). Amblotherium (including SDSM 148545) demonstrates a more dramatic increase in molar crown height from position m1 to m3 compared to Dryolestes and Laolestes, as indicated by the ratio of m3 crown height to that of m1 (table 3). SDSM 148545 differs from other species of Am- blotherium in having a dentary length and molar me- sial-distal length more similar to Dryolestes (table 3). The lengths of m3 in Dryolestes and SDSM 148545 are approximately 1.5 mm in each case, whereas the mean of four specimens of A. pusillum and A. gracile is 0.80 mm (Simpson, 1928, 1929), a size increase of approxi- mately 87.5% from other species of Amblotherium to A. megistodon (SDSM 148545). The Little Houston Quarry jaw also differs from other species of Amblotherium in having the roots of m1 and m2 being unequal in size, as in the positions from m3 back; in some specimens of other species the first two molars have “normal” roots of equal size. Phylogenetic analysis, incorporating the matrix of Rougier and others (2012) and adding two characters (appendix), places SDSM 148585 among dryolestids in a polytomy with Amblotherium (based on A. pusil- lum and A. gracile), Comotherium, and Laolestes+Groe- bertherium, with Dryolestes as a sister taxon to the clade (figure 20). The unresolved nature of the Comotheri- um-Amblotherium-SDSM 148545 polytomy is likely caused by missing data in SDSM 148545, particular- ly in the less well preserved posterior dentary region and in the lack of upper jaws. In Rougier and others (2012) this relationship (minus SDSM 148545) was resolved as Dryolestes+(Comotherium+([Amblotheri- um+(Laolestes+Groebertherium)]). Comotherium was described as a dryolestid (Prothero, 1981) but has since been classified as a paurodontid by others (Martin, 1999; Kielan-Jaworowska and others, 2004). Discussion The jaw length as preserved (~22 mm) suggests a mass estimate for Amblotherium megistodon of 33.2 g, compared with estimates of 25.9 g for other species of Amblotherium, 71.3 g for Laolestes, and 103.7 g for Dryolestes (Foster, 2009). However, the facts that SDSM 148545 appears to be a juvenile and that the length of m3 is essentially the same as in adult Dryolestes suggest that the adult animal likely would have approached Laolestes and Dryolestes in mass. At the very least, the complete dentary of SDSM 148545, with the missing anterior and posterior ends restored, was likely close to 26 mm long, a length indicating a possible mass of 54.5 g (formula of Foster, 2009), a size making A. megistodon the ninth largest mammal in the Morrison mammal fauna (of 22). Amblotherium gracile, in contrast, is the sixth smallest in the group. Amblotherium comprises the species A. gracile from the Upper Jurassic Morrison Formation and A. pusil- lum from the Upper Jurassic-Lower Cretaceous Pur- beck Group of England (Simpson, 1928, 1929; Martin, 1999, 2000; Kielan-Jaworowska and others, 2004; Ave- 57 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 rianov and others, 2013, 2014). Amblotherium gracile includes A. debile and Miccylotyrans (Averianov and others, 2013) and is known from Como Bluff (Quarry 9 and Chuck’s Prospect), Dinosaur National Monument (Rainbow Park), and Garden Park (Marsh-Felch) in the Morrison Formation. Amblotherium megistodon is then a second species within the Morrison Formation. In addition to partial jaws of Amblotherium gracile from Quarry 9 at Como Bluff (Simpson, 1929), several re- ferred lower molars from the Rainbow Park microver- tebrate sites at Dinosaur National Monument were de- scribed by Engelmann and Callison (1998). These latter teeth were small and of an “A. debile” size of 0.62 to 0.72 mm length, in contrast to A. megistodon’s molar length of ~1.5 mm The presence of a species of Amblotherium in the Morrison Formation that is more than 87% larger than A. gracile suggests that either there were two co-exist- ing and niche-partitioned species present in the region during the Late Jurassic or that the genus underwent body-size evolution over the course of Morrison times. Because of the inability to correlate the very thin Mor- rison Formation of the Black Hills to other, thicker sec- tions in Wyoming or elsewhere, it is unclear if A. megist- odon represents a larger contemporary of A. gracile or if it represents an anagenetic change in body size within Am- blotherium through some part of the ~7 million years of the formation. If the latter, it is even unclear whether the change in body size would have been an increase or de- crease. On the other hand, a larger but contemporaneous species in the northern part of the Morrison Formation could indicate some degree of paleobiogeographic seg- regation within the genus, but this is not yet conclusive. BONE MODIFICATIONS Many of the sauropod bones from the Little Hous- ton Quarry (but far fewer of the bones of smaller taxa such as neornithischians) possess a few to near-com- Table 3. Comparison of features of various dryolestid mammal jaws from the Morrison Formation. All measurements in mm. Morganucodonta Docodontids Triconodontids Symmetrodontids Monotremes Henkelotherium Dryolestes Comotherium Amblotherium SDSM 148545 Laolestes Groebertherium Paurodontids Meridiolestids Eutherians Metatherians A. megistodon Figure 20. Simplified phylogenetic tree based on strict con- sensus of 12 MTPs from analysis of 60 taxa and 319 charac- ters (length = 1226), showing relationships of SDSM 148545 (Amblotherium megistodon) and other dryolestids. Red text indicates taxa with representatives in the Morrison Forma- tion; yellow box indicates traditional Dryolestida. Dryolestes Laolestes Amblotherium SDSM 148545 Dentary Length 30.5 27.5 18.2 ~22.0 (Gui Mam 130/75) (YPM 13719) (BMNH 47752) Length m3 1.5 1.25 0.8 1.5 Dentary depth: length 0.132 0.14 0.111 ~0.106 Height m3: Dentary depth (mean) 0.366 0.362 0.707 0.657 (N=3) (N=2) (N=4) Height m3:m1 (mean) 1.29 1.14 1.65 1.38 (N=4) (N=1) (N=3) 58 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 plete covering of surficial pits, especially along the shafts of long bones (figure 21). These pits are similar to those described as being caused by low pH soil conditions or alternatively by boring dermestid beetles or their larvae (Fiorillo, 1998; Britt and others, 2008; Bader and oth- ers, 2009). Most sauropod limb elements from the Little Houston Quarry have at least some of these pits, and a number of elements are almost completely covered in them. These modifications suggest at least some sub- aerial exposure or burial in acidic soils for many of the sauropod elements from the site. THEROPOD(?) TRACKS Several small, tridactyl dinosaur tracks of a Gralla- tor-like morphology were found in a sandstone block displaced from just below the quarry level (figure 22), and these were described by Foster and Lockley (1995). These tracks probably represent small theropod dino- saurs, though some may possibly have been made by small neornithischians. DISCUSSION Paleoenvironmental Setting The Little Houston Quarry contains a very dense deposit of vertebrate material ranging in size from large sauropod dinosaurs to microvertebrates in thin and laterally restricted layers of an elongate, ribbon-shaped deposit above a channel sandstone (figure 23). The de- posit is laterally restricted to the space between visible edges incised into variegated floodplain mudstones and is much longer than wide (“ribbon” geometry). The transition from a thin and laterally restricted channel sandstone (with mud clasts) into the quarry interval of interbedded green claystone and sometimes laminated, clay-ball bearing siltstone (figure 2B), similarly lateral- ly restricted, and then into pure floodplain mudstone, all suggests a gradually in-filling abandoned channel that was occasionally reactivated during floods (Foster, 2001; e.g., Miall, 2010). The quarry layer itself probably represents the laminated fill unit of a fully disconnect- ed channel (e.g., Toonen and others, 2012), and most well-preserved microvertebrate bone elements within the deposit are probably parautochthonous to autoch- thonous (Behrensmeyer, 1988; Foster, 2001; Rogers and Brady, 2010). Taphonomy The Little Houston Quarry contains microvertebrate material in great abundance and in relatively highly de- fined layers but with a high degree of disarticulation (~100%) and fragmentation, and its lithology consists of siltstone with heterogeneous clasts of clay balls and small bone fragments (Foster, 2001). It thus represents a broad Type 1 pond deposit taphofacies for microver- tebrate remains in the Morrison Formation, along with Figure 21. Modifications of sauropod dinosaur bones from the Little Houston Quarry. (A) Pitting on shaft of sauropod ulna SDSM 35952. (B and C) Near-total coverage by pitting on a sauropod metapodial MWC 5784. Scale bars in cm. 59 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 the Small Quarry at Garden Park, Colorado, and Quar- ry 9 at Como Bluff, Wyoming (Foster, 2001, 2003). This taphofacies contrasts markedly with broad Type 2 pond deposits typical of the Morrison Formation of the Col- orado Plateau, the latter consisting of usually “clean” grayish mudstone with a very low-density deposit of sometimes articulated or associated material, including whole or partial skeletons of microvertebrates such as mammals and sphenodontians (Foster 2001, 2003); lo- calities of this type include the Callison and Tom’s Place sites at the Fruita Paleontological Area, Colorado (Cal- lison, 1987; Kirkland, 2006), Rainbow Park 94 and 96, Dinosaur National Monument (Evans and Chure, 1998, 1999; Evans and others, 2005), Wolf Creek, Colorado (Wood, 1986), and Cisco Mammal Quarry, Utah (Davis and others, 2018). Matrix samples from Little Houston, Small Quarry, and Quarry 9 placed side by side can be almost indistinguishable from each other and would presumably represent somewhat similar pond settings, although the details of their respective settings differ. The Little Houston Quarry, situated on top of a channel sand, appears to represent the in-filling of an abandoned channel pond (Foster, 2001), whereas Quarry 9, the main fossiliferous lens of which was under a sandstone (Carrano and Velez-Juarbe, 2006), probably represents a floodplain pond followed by avulsion of a main river channel. The Small Quarry microvertebrate layer is just below a crevasse-splay sandstone series (Rougier and others, 2015) and was probably in a floodplain pond and apparently near a river channel as well. So far, Type 1 pond deposits (Little Houston, Small Quarry, Quarry 9) are restricted to the northern and eastern parts of the Morrison Formation, and Type 2 deposits (FPA, Rainbow Park, Wolf Creek, and Cisco Mammal) are only known from the Colorado Plateau region in the Morrison. This taphofacies segregation may reflect the relative abundance differences in the occurrences of turtles and semi-aquatic crocodyliforms between the Colorado Plateau and areas north and east (Foster and McMullen, 2017), the north- and east-re- stricted distributions of possibly semi-aquatic mamma- lian and archosauromorph taxa in Docodon and Cte- niogenys (Chure and Evans, 1998; Foster and Trujillo, 2000; Foster and others, 2006), and geologic evidence suggesting a higher water table and wetter surface con- ditions during Morrison times in areas that are now parts of Wyoming and eastern Colorado (Turner and Peterson, 2004). The Little Houston Quarry therefore helps characterize the faunas of the northern and east- ern “wet” setting of the Morrison Formation. In contrast to the microvertebrate material, up to 25% of dinosaur material in the quarry is in articula- tion, although the dinosaur material is part of the same dense accumulation as the small taxa. Almost uniquely, microvertebrate remains occur in among the articulat- ed and disarticulated dinosaur remains as well, with some mammal jaws from the mammal pit being found centimeters away from an articulated series of Camara- saurus caudals. Paleobiodiversity With at least 26 vertebrate taxa preserved (and 35 Figure 22. Tridactyl (theropod?) dinosaur track on sandstone slab from channel just below Little Houston Quarry (see Fos- ter and Lockley, 1995). Scale bar numbered in inches. 60 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 taxa total), the biota from the Little Houston Quarry is the second-most diverse single locality in the Morrison Formation after Reed’s Quarry 9 (Foster, 2003), the latter at 76 species (72 vertebrates; Carrano and Velez-Juarbe, 2006). The Little Houston Quarry represents the most diverse Morrison Formation locality north of Como Bluff, Wyoming, and it is important for studying what seems to be a newly recognized “northern fauna” of the unit (e.g., Maidment and others, 2018). The Little Hous- ton Quarry is followed closely in vertebrate diversity by the Dry Mesa Quarry of Colorado, and then several others. Beyond the shared taphonomic characteristics, the biota of the Little Houston Quarry shares with Quarry 9 and the Small Quarry several faunal similarities: (1) a relative abundance of Docodon specimens among the mammalian genera (Little Houston and Small appear to specifically share the species D. apoxys); (2) a rela- tive abundance of Cteniogenys (so far absent at Small); (3) actinopterygian fish represented by vertebrae, teeth, and jaw fragments; (4) the lungfish Ceratodus fossan- ovum (Little Houston and Quarry 9 at least); and (5) relatively abundant turtles and semi-aquatic crocody- liforms. These are taxa and patterns that are absent or rare in Type 2 deposits on the Colorado Plateau. Most of the diversity at the Little Houston Quarry is among microvertebrate taxa, and several of the species are particularly rare in other parts of the Morrison For- mation. Among these latter taxa are the potentially new, elongate unionid bivalves (figures 5E and 5F), the first occurrence of the atoposaurid crocodyliform Theriosu- chus in the Morrison Formation (figures 12A to 12C), several unusual small theropod tooth types (figures 13 and 14), a new species of Amblotherium (figure 19), and the first occurrence of the mammal Docodon apoxys outside its type locality (figure 18). The abundance of aquatic and semi-aquatic taxa in the deposit reflects the abandoned channel pond setting. The diversity of the biota is probably not unusual for the paleoenvironment of the northern Morrison Formation but more likely is a product of preservation in a highly concentrated deposit. The Morrison Formation of the Black Hills of Wy- oming and South Dakota may preserve even more taxa than are currently known, including possibly new spe- cies, but it has been difficult to fully compare the biota from the area to other parts of Wyoming and the Colo- rado Plateau due to the thinness of the unit in the Black Hills and the apparent lack of smectitic mudstones, both preventing lithostratigraphic correlations or radiomet- ric age comparisons (e.g., Turner and Peterson, 1999; Trujillo and Kowallis, 2015). The diverse biota present at the Little Houston Quarry, and the unusual taxa pre- served there, suggest that the region may yet hold even more information about the apparent “northern fauna” of the Morrison Formation. Quarry Unit: Light greenish-gray (5GY 8/1) to light olive gray (5Y 6/1) laminated siltstone and very �ne grained sandstone interbedded with dark greenish-gray (5GY 4/1) to grayish-olive (10Y 4/2) claystone; siltstone layers approximately 3-20 cm thick; claystone layers approximately 1-4 cm thick; abundant greenish-gray clay clasts in some siltstone layers; laminations in siltstone are planar to wavy; abundant carbonized plant remains in some siltstone layers; two microvertebrate layers (*) up to approximately 10 cm thick in lower part of unit, containing abundant disarticulated but well-preserved bones Light tan, �ne- to very �ne grained sandstone; moderate- ly well sorted and rounded grains; 1-5 cm planar tabular and trough cross-beds; rounded clasts of calcium carbonate and clay common near base and center of channel; some well- rounded bone fragments near base; minor amount of recog- nizable turtle shell and croc- odyliform teeth Light gray limestone Light gray limestone Gray and maroon claystone Dark greenish gray, gray-olive, and maroon claystone; rootcast Light tan �ne- to very �ne grained sandstone; some cross-beds; present above main pit only Dark greenish-gray claystone 1 m * * Figure 23. Stratigraphic section of Morrison Formation ex- posure at the Little Houston Quarry showing position of main bone layers (*) above thin channel sandstone. 61 An Unusually Diverse Northern Biota from the Morrison Formation (Upper Jurassic), Black Hills, Wyoming Foster, J.R., Pagnac, D.C., and Hunt-Foster, R.K. Geology of the Intermountain West 2020 Volume 7 ACKNOWLEDGMENTS Special thanks for discussions, information, tech- nological assistance, help with figures, and help track- ing down publications to (in no particular order): Susie Maidment (The Natural History Museum, London), Carole Gee (University of Bonn), Peter Galton (Univer- sity of Bridgeport, retired), Nick Fraser (National Mu- seums Scotland), Susan Evans (University College Lon- don), Ken Carpenter (Prehistoric Museum, Utah State University–Eastern), Scott Madsen (Utah Geological Survey, retired), Tom Holtz (University of Maryland), Bryan Small (Museum of Texas Tech University), Jim Martin (University of Louisiana at Lafayette), Guillermo Rougier (University of Louisville), Lisa Baldwin (Na- tional Park Service), Tracy Ford (independent), Dale Malinzak (Black Hills State University), Dan Chure (National Park Service, retired), Kelli Trujillo (Laramie County Community College), Robin Beck (University of Salford), and Brian Davis (University of Louisville). Thanks to crews from the SDMS Museum of Geology and the MWC for their work at the site over the years and to the landowners for access. Microphotography facilitated by the South Dakota School of Mines and Technology Museum of Geology and Ben Burger (Utah State University, Uintah Basin). Finally, thanks to Chris Noto (University of Wisconsin, Parkside), Jim Kirkland (Utah Geological Survey), and Kelli Trujillo (Laramie County Community College) for review comments on the manuscript. REFERENCES Allen, E.R., 2012, Analysis of North American goniopholidid crocodyliforms in a phylogenetic context: Iowa City, Uni- versity of Iowa, M.S. thesis, 89 p. Anderson, L.C., 2014, Ultra-elongate freshwater pearly mussels (Unionida)—roles for function and constraint in multiple morphologic convergences with marine taxa, in Hembree, D.I., Platt, B.F., and Smith, J.J., editors, Experimental ap- proaches to understanding fossil organisms: Topics in Ge- obiology 41, p. 21–47. 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