Journal of Systematic Palaeontology



A CRITICAL RE-EVALUATION OF THE LATE TRIASSIC DINOSAUR TAXA OF NORTH AMERICA


Sterling J. Nesbitt a1, Randall B. Irmis a2 and William G. Parker a3
a1 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
a2 Museum of Paleontology and Department of Integrative Biology, 1101 Valley Life Sciences Building, University of California, Berkeley, CA 94720–4780, USA
a3 Division of Resource Management, Petrified Forest National Park, P.O. Box 2217, Petrified Forest, AZ 86028, USA

Article author query
nesbitt sj   [PubMed][Google Scholar] 
irmis rb   [PubMed][Google Scholar] 
parker wg   [PubMed][Google Scholar] 

Abstract

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.