Redescription of the holotype specimen of Chindesaurus bryansmalli Long and Murry, 1995 (Dinosauria, Theropoda), from Petrified Forest National Park, Arizona

ABSTRACT

Chindesaurus bryansmalli is an early dinosaur of uncertain affinities from the Late Triassic Chinle Formation at Petrified Forest National Park, Arizona. Since its first description in 1995, the taxon has been considered a plateosaurid, a non-eusaurischian saurischian, a herrerasaurid, and/or a non-neotheropod member of Theropoda. Chindesaurus bryansmalli is usually scored for about 25% of the characters in a given phylogenetic analysis, and many characters have been scored secondhand from misidentified elements. Here, we provide a redescription of the holotype specimen of C. bryansmalli, correct misidentifications, introduce previously unknown elements, and discuss novel morphological character observations. Chindesaurus bryansmalli is supported as the sister taxon to the non-neotheropod theropod Tawa hallae from the Chinle Formation at Ghost Ranch, New Mexico. The same two most parsimonious trees, with increasing node support, result from iteratively removing the three most incomplete taxa in the employed data set, suggesting that the relationships of stem-averostran theropods are not highly affected by the inclusion of fragmentary specimens. The Chindesaurus + Tawa clade recovered here may represent a potentially diverse group of early theropods prior to the end-Triassic mass extinction.

ACKNOWLEDGMENTS

We thank the Labaratório de Paleontologia at the Universidade de São Paulo, Ribeirão Preto, the Jackson School of Geosciences at the University of Texas at Austin, and the Petrified Forest Museum Association for funding this work and the Congreso Latinoamericano de Paleontologia for the invitation to present our research at the fifth conference in Colonia del Sacramento, Uruguay. We thank T. Rowe, C. Bell, J. Clarke, D. Stockli, and H.-D. Sues for reviewing an early draft of the manuscript. M. Smith (PEFO), P. Holroyd, K. Padian, and M. Goodwin (UCMP), B. Sanders (UMMP), A. Downs (GR), and C. Sagebiel and M. Brown (TMM) provided access to specimens. We especially thank R. Long and T. Rowe for discussions on the excavation and preparation of the holotype of Chindesaurus bryansmalli. We thank T. Rowe, L. Gordon, H. Hutchison, N. Simmons, K. Ballew, B. Small, and the late M. Greenwald for collecting the holotype specimen. R. Long’s field notes are on file in the PEFO museum archives. We thank M. Bronzati and J. Marsola for helpful comparative photographs. Reviews by R. Butler and M. Ezcurra enhanced the manuscript. This is Petrified Forest National Park Contribution No. 63. The conclusions presented here are those of the authors and do not represent the views of the United States Government.

ORCID

Adam D. Marsh http://orcid.org/0000-0002-3223-8940

William G. Parker http://orcid.org/0000-0002-6005-7098

Max C. Langer http://orcid.org/0000-0003-1009-4605

Sterling J. Nesbitt http://orcid.org/0000-0002-7017-1652