Anatomy and ontogeny of the "carnivorous aetosaur": New information on Coahomasuchus kahleorum (Archosauria: Pseudosuchia) from the Upper Triassic Dockum Group of Texas.

Abstract

A newly referred specimen of Coahomasuchus kahleorum (TMM 31100-437) from the lower part of the Upper Triassic Dockum Group of Texas preserves much of the skeleton including the majority of the skull. Introduced in the literature in the 1980s as the "carnivorous aetosaur", TMM 31100-437 bears recurved teeth that previously were considered unique among aetosaurs. The small size of the individual led to speculation that it represents a skeletally immature individual that retains a plesiomorphic dentition for Archosauromorpha. We provide a detailed evaluation of the anatomy and phylogenetic relationships of this specimen. Apomorphies of the osteoderms and braincase support the referral of the specimen to C. kahleorum. Histological analysis of the femur demonstrates that TMM 31100-437 does not represent a juvenile form of another known aetosaur. Thus, TMM 31000-437 provides another case demonstrating that aetosaur species spanned a wide range of maximum body sizes, from approximately 1.5 m to over 5 m in length. Reanalysis of the type specimen of C. kahleorum, along with information from TMM 31000-437, demonstrates that the lateral osteoderms are not autapomorphic as previously described and have distinct lateral and medial flanges as well as a dorsal eminence. Overall, this specimen provides key details regarding body size and diet in an early occurring aetosaur.