NEW SPECIMENS OF CALYPTOSUCHUS WELLESI (PSEUDOSUCHIA: AETOSAURIA) FROM THE UPPER TRIASSIC CHINLE FORMATION OF PETRIFIED FOREST NATIONAL PARK, ARIZONA, PROVIDE NEW DETAILS ON THE CRANIAL ANATOMY AND INTRASPECIFIC VARIATION OF THE TAXON

Calyptosuchus wellesi is an aetosaur currently known from the upper Blue Mesa Member and lower Sonsela Member of the Upper Triassic Chinle Formation (northern Arizona) and the Tecovas Formation of the Dockum Group (northwestern Texas). Because of its restricted stratigraphical range, this taxon is considered biostratigraphically informative and provides a means of correlating upper Triassic strata in the southwestern United States (U.S.). Currently, our anatomical understanding of C. wellesi is based on a combination of the holotype specimen (UMMP 13950), a referred partial pelvis (UMMP 7470) from Texas, and an array of referred disarticulated elements from the Placerias Quarry of Arizona.

Here, we present two new specimens referrable to C. wellesi that were collected from the upper Blue Mesa Member of the Chinle Formation within Petrified Forest National Park (PEFO), Arizona. PEFO 49321 includes associated maxillae with dentition, a jugal, quadratojugal, quadrate, laterosphenoid, surangular, prearticular, and articular. This provides new details of the skull morphology of C. wellesi allowing us to explore new phylogenetic hypotheses and assess the diet of this taxon. The second specimen, PEFO 46222, is a partial associated skeleton, preserving a nearly complete pelvis, vertebrae, and osteoderms from the trunk through caudal regions. PEFO 46222 provides new insight into the morphological variation of the osteoderms within the carapace of one individual; this includes variation in the development of the dorsal eminence and the degree of flexure of both the paramedian and lateral osteoderms across the various subdivisions of the carapace. Understanding the degree of variation in the aetosaur carapace is important for the biostratigraphic utility of aetosaurs. The preserved pelvic girdle of PEFO 46222 provides new details into the intraspecific variation of the non-osteoderm postcrania of C. wellesi. We document the first occurrence of co-ossified sacral vertebrae within C. wellesi – the first documentation of this state outside the Desmatosuchini. Additionally, the ilium and ischium show significant morphological variation from the referred elements collected from the Placerias Quarry, bringing to question the taxonomic affinities of this referred material.