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 orni- thomimosaurs than to any other theropod clade, and treat- ed 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 descrip- tion of the specific outline of the proximal facet, which must articulate with the corresponding penultimate phal- anx, 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 dem- onstrating 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 large- ly 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 curva- ture 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 charac- ters. 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 prox- imal 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 un- guals of the ornithomimid Gallimimus. In a Struthiomimus manus figured by Osborn (1917: fig. 3), the flexor tuber- cles 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 distri- bution 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 incom- pletely understood interval in the history of ornithomi- mosaurs. It contains the globally youngest occurrences of (non-ornithomimid, non-deinocheirid) ‘basal ornithomi- mosaurs’ and oldest occurrences of possible basal deino- cheirids (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 ornitho- mimosaurs from the Cenomanian to Santonian of North America (McFeeters et al. 2016). The presence of coex- isting 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 ornithomi- mosaurs, we remain cautious of such far-reaching claims given the current state of evidence. 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