BONEBED OF A CARNIVOROUS ARCHOSAUROMORPH FROM THE CHINLE FORMATION (LATE TRIASSIC: NORIAN) OF PETRIFIED FOREST NATIONAL PARK

Allokotosauria is a lineage of non-archosaur archosauromorphs that experienced rapid diversification after the end-Permian mass extinction and was ecologically diverse and anatomically disparate. The recently-named clade comprises Pamelaria, Trilophosauridae (Teraterpeton, Spinosuchus, and Trilophosaurus), and Azendohsauridae. Azendohsaurids have long been interpreted as anything but the sister group to trilophosaurids; the type species of Azendohsaurus, A. laaroussii, was first thought to be sauropodomorph dinosaur from the Late Triassic of Morocco. Except for A. madagaskarensis, most of the fossil record of Azendohsauridae comprises isolated and fragmentary individuals, and the biology of the group, including skeletal ontogeny, is unknown or poorly understood. Here, we report an azendohsaurid bonebed from the Late Triassic Chinle Formation at Petrified Forest National Park (PEFO), AZ. The new bonebed was discovered in 2014 in the Dying Grounds locality (PFV 122), one of the most fossil-rich and heavily-prospected areas in the park. Since then, more than 900 bones have been removed from the quarry and include a growth series of at least nine individuals. The majority of the bones (>90%) belong to the azendohsaurid, but isolated elements of other taxa are also recognized including sharks and actinopterygians, metoposaurids, archosauriforms, and a dinosauromorph. All of the bones are disarticulated, non-associated, and occur in a matrix-supported fine-grained sandstone overlaying a homogenous purple paleosol, interpreted to represent a crevasse-splay. Postcranial elements are very similar to known allokotosaurids, however, cranial material includes dentulous maxillae and premaxillae with large recurved and serrated teeth that differ significantly from the denticulated and presumably herbivorous teeth of both species of Azendohsaurus, as well as the transversely broadened teeth of Trilophosaurus. Thus, although the postcranial skeleton appears to be strongly conserved across the Allokotosauria, cranial elements show that members of the clade were ecologically disparate. This new material also affords the first opportunity to examine intraspecific variation in an archosauriform species as well as skeletal ontogeny of an azendohsaurid using long-bone histology of a growth series.