Paper No. 10
Presentation Time: 4:15 PM
THE EARLY EVOLUTION OF CROCODYLOMORPHA: NEARLY COMPLETE SKELETONS FROM THE LATE TRIASSIC OF NORTH CAROLINA DEMONSTRATE CONSERVATION IN THE EARLY BODY PLAN OF A SUCCESSFUL CLADE
Crocodylomorpha, the group that includes extant Crocodylia and their relatives, first appeared in the fossil record in the Late Triassic and quickly spread across Pangea. However, the early evolution of the group is poorly understood because specimens of early crocodylomorphs are small and subject to preservational biases; therefore, they are generally rare in Late Triassic assemblages, and when found, the skeletons are almost always disarticulated and only partially preserved. Two crocodylomorph specimens from the Upper Triassic Deep River Basin of North Carolina, the recently named Dromicosuchus grallator and a new skeleton presented here (specimen North Carolina Museum of Natural Sciences [NCSM] 21722), represent the most complete early crocodylomorphs found to date. These extraordinary specimens preserve much of the skull and skeleton in articulation and typify the first persistent crocodylomorph body plan. In contrast to their extant cousins, early crocodylomorph possessed dorsoventrally deep skulls, long and gracile hindlimbs and forelimbs, and a parasagittal limb orientation. Given that NCSM 21722 is from the late Carnian and thus one of the oldest crocodylomorphs, it is remarkable that Dromicosuchus grallator, NCSM 21722, and the Coelophysis Quarry Hesperosuchus share an extremely similar anatomy even though these specimens span 20-25 million years. The new specimen (NCSM 21722) lies in nearly complete articulation and demonstrates that the small hands and relatively larger feet of extant crocodylians, was present in the earliest crocodylomorphs. Additionally, the new specimen shows that much of the tail was surrounded by small osteoderms. These nearly complete skeletons from North Carolina help clarify anatomical details of early crocodylomorphs from the Late Triassic of western North America. For example, our comparisons of NCSM 21722 and Hesperosuchus agilis indicate that part of the type of H. agilis represents a mix of animals. Placed in the context of the early crocodylomorph fossil record, these new data demonstrate the body plan typified by the Late Triassic crocodylomorphs from North Carolina survives for 70 million years until disappearing in the Late Jurassic.