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

Abstract

ABSTRACTChindesaurus 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.