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A Critical Re-Evaluation of the Late Triassic Dinosaur Taxa of North America

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A Critical Re-Evaluation of the Late Triassic Dinosaur Taxa of North America See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/231845935 A critical re-evaluation of the Late Triassic dinosaur taxa of North America Article in Journal of Systematic Palaeontology · June 2007 DOI: 10.1017/S1477201907002040 CITATIONS READS 129 523 3 authors, including: Sterling Nesbitt William G Parker Virginia Polytechnic Institute and State University National Park Service 140 PUBLICATIONS 3,958 CITATIONS 129 PUBLICATIONS 1,433 CITATIONS SEE PROFILE SEE PROFILE Some of the authors of this publication are also working on these related projects: Development and systematics of Late Triassic metoposaurid temnospondyls View project Carnufex carolinensis - A new species of large-bodied basal crocodylomorph View project All content following this page was uploaded by William G Parker on 29 May 2014. The user has requested enhancement of the downloaded file. Journal of Systematic Palaeontology 5 (2): 209–243 Issued 25 May 2007 doi:10.1017/S1477201907002040 Printed in the United Kingdom C The Natural History Museum A critical re-evaluation of the Late Triassic dinosaur taxa of North America Sterling J. Nesbitt American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024, USA and Lamont-Doherty Earth Observatory, Columbia University, 61 Rt. 9W, Palisades, NY 10964, USA Randall B. Irmis Museum of Paleontology and Department of Integrative Biology, 1101 Valley Life Sciences Building, University of California, Berkeley, CA 94720–4780, USA William G. Parker Division of Resource Management, Petrified Forest National Park, P.O. Box 2217, Petrified Forest, AZ 86028, USA SYNOPSIS The North American Triassic dinosaur record has been repeatedly cited as one of the most complete early dinosaur assemblages. The discovery of Silesaurus from Poland and the recognition that Herrerasaurus and Eoraptor may not be theropods have forced a re-evaluation of saurischian and theropod synapomorphies. Here, we re-evaluate each purported Triassic dinosaur from North America on a specimen by specimen basis using an apomorphy-based approach. We attempt to assign specimens to the most exclusive taxon possible. Our revision of purported Late Triassic dinosaur material from North America indicates that dinosaurs were rarer and less diverse in these strata than previously thought. This analysis concludes that non-dinosaurian dinosauriforms were present in North America in the Late Triassic. Most of the proposed theropod specimens are fragmentary and/or indistinguishable from corresponding elements in the only well-known Triassic theropod of North America, Coelophysis bauri. No Triassic material from North America can be assigned to Sauropodomorpha, because none of the purported ‘prosauropod’ material is diagnostic. Recent discovery of the skull and skeleton of Revueltosaurus callenderi from Arizona shows that it is a pseudosuchian archosaur, not an ornithischian dinosaur. As a result, other purported North American ornithischian teeth cannot be assigned to the Ornithischia and therefore, there are no confirmed North American Triassic ornithischians. Non-tetanuran theropods and possible basal saurischians are the only identifiable dinosaurs recognised in North America until the beginning of the Jurassic Period. KEY WORDS Dinosauria, Ornithischia, Saurischia, Theropoda, Triassic, early diversity Contents Introduction 210 Methods 210 Institutional Abbreviations 211 Putative theropods 211 New Mexico 211 Eucoelophysis baldwini Sullivan & Lucas, 1999 211 Snyder Quarry ‘dinosaur’ material 214 Coelophysis bauri Cope, 1889 218 Coelophysis material of Cope 220 Gojirasaurus quayi Carpenter, 1997 220 Bluewater Creek Member ‘theropod’ material 222 Santa Rosa Formation ‘theropod’ material 222 Arizona 222 Coelophysis sp. (Padian, 1986) 222 ‘Camposaurus arizonensis’ Hunt et al., 1998 222 Other Placerias Quarry material 223 Texas 223 Protoavis texensis Chatterjee, 1991 223 210 S. J. Nesbitt et al. Shuvosaurus inexpectatus Chatterjee, 1993 224 Spinosuchus caseanus von Huene, 1932 225 Putative herrerasaurids 225 Caseosaurus crosbyensis Hunt et al., 1998 225 Chindesaurus bryansmalli Long & Murry, 1995 226 NMMNH P-4569 229 NMMNH P-17375 229 Arctosaurus osborni Adams, 1875 229 Putative ornithischians 230 Technosaurus smalli Chatterjee, 1984 230 TTUP unnumbered 232 Putative ‘prosauropods’ 232 Discussion 233 Other evidence 234 Timing of the early diversity of dinosaurs in North America 235 The Triassic record outside North America 236 Conclusions 237 Acknowledgements 237 References 237 Appendix 242 Introduction current phylogenetic hypotheses concerning the placement of controversial taxa (e.g. Eoraptor and Herrerasaurus). Our The origin of the Dinosauria lies in the Late Triassic Period goal in this study is to determine which specimens in the (Gauthier 1986; Langer 2004; Langer & Benton 2006): how- Late Triassic of North America can be unambiguously iden- ever, our understanding of the early history and relationships tified as members of Dinosauria. We do not specify the exact of dinosaurs remains poor because of the absence of well phylogenetic position of these taxa within Dinosauria, a task preserved crania and postcrania for most basal dinosaurs and that requires a comprehensive specimen-based phylogenetic a poor understanding of the character polarities of dinosaurs analysis that is beyond the scope of the present work. and their immediate outgroups (Fraser et al. 2002). Further- more, a lack of consensus of the phylogenetic placement of controversial taxa such as Herrerasaurus inside Theropoda Methods (Sereno & Novas 1993; Novas 1993), as a stem saurischian (Langer 2004) or outside Dinosauria (Holtz & Padian 1995; Revision of the diagnoses of Dinosauromorpha, Dinosauri- Fraser et al. 2002)) hampers our understanding of the ori- formes and Dinosauria is beyond the scope of this paper gin, early biogeography and diversity of the Dinosauria. A and can only be completed after a comprehensive phylogen- new distribution of character states among ornithodirans and etic analysis. Because there is no consensus regarding the basal archosaurs (including crocodile-line archosaurs) has diagnosis of Dinosauria (see Sereno & Novas 1993; Sereno emerged with the discovery of taxa such as Silesaurus (Dzik 1999; Holtz & Padian 1995; Fraser et al. 2002; Langer &- 2003), Effigia okeeffeae (Nesbitt & Norell 2006) and Re- Benton 2006) and its immediate outgroups, we use an vueltosaurus (Parker et al. 2005) and has led to new insights apomorphy-based approach. That is, we use specimen by spe- regarding the identification of crocodile-line archosaurs, or- cimen comparisons and highlight character states that have nithodirans, dinosauromorphs, dinosauriforms and members previously been used in phylogenetic analyses to place taxa of the Dinosauria in the Triassic. within specific clades. We cannot always assign a specimen Recently, many Late Triassic dinosaur specimens have to a species-level taxon, so we assign specimens to the least been described from around the world (see Heckert & Lucas inclusive clade possible using apomorphies. The most useful 2000), especially from the western United States (Hunt 1991; character states for identification of members of Dinosauria Carpenter 1997; Hunt et al. 1998; Sullivan & Lucas 1999; are illustrated in Fig. 1. Heckert & Lucas 2000). The apparently high diversity of We recognise that some of the taxa considered here dinosaurs in the western United States (Hunt et al. 1998) has may fall within the Dinosauria in future phylogenetic ana- been compared with the European (Rauhut & Hungerbuhler¨ lyses; however, the lack of certain character states that place 2000) and South American (Heckert & Lucas 2000) Triassic a taxon within Dinosauria may be a result of reversals (e.g. dinosaur faunas. a nearly closed acetabulum) and/or missing data in other Here, we re-examine each purported Triassic dinosaur important regions of the body (e.g. the skull of Chindes- from North America on a specimen by specimen basis. We aurus is not known), as exemplified by many of the purpor- employ a conservative approach in our assignments to spe- ted Late Triassic dinosaurs of North America. Only after a cific or more general clades that are unaffected by the various rigorous phylogenetic analysis, which is not provided herein, Re-evaluation of North American Late Triassic dinosaur taxa 211 below with the exception of Arctosaurus.CastsofLeso- thosaurus tibiae described by Knoll & Battail (2001) were also examined. Descriptions of Lesothosaurus, Thecodonto- saurus, Plateosaurus, Coelophysis rhodesiensis,‘Syntarsus’ kayentakatae, Liliensternus and Arctosaurus were taken from the literature. Unpublished photographs of Silesaurus mater- ial were also used. Institutional Abbreviations AMNH, American Museum of Natural History, New York, NY; FMNH, Field Museum of Natural History, Chicago, IL; MNA, Museum of Northern Arizona, Flagstaff, AZ; NMI, National Museum of Ireland; NMMNH, New Mexico Mu- seum of Natural History, Albuquerque, NM; PEFO,Petri- fied Forest National Park, AZ; TTUP, Texas Tech University Paleontology Collections, Lubbock, TX; UCM, University of Colorado Museum, Boulder, CO; UCMP, University of California Museum of Paleontology, Berkeley, CA; UMMP, University of Michigan Museum of Paleontology, Ann Ar- Figure 1 Dinosaur specimens displaying character states used to bor, MI; YPM, Yale Peabody Museum, New Haven, CT. diagnose Dinosauria in the text. (A) left ilium of the holotype of Dilophosaurus wetherilli
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