Paper No. 9
Presentation Time: 3:55 PM
A LARGE-BODIED CROCODYLOMORPH WITH EXTENSIVE CRANIAL ORNAMENTATION FROM THE UPPER TRIASSIC CHATHAM GROUP OF NORTH CAROLINA
Crocodile-line archosaurs underwent a rapid radiation in the wake of the end-Permian mass extinction and came to dominate terrestrial ecosystems by the Late Triassic. The only pseudosuchians to survive the end-Triassic extinction were crocodylomorphs, whose early bauplan consisted, in large part, of gracile, small-bodied, terrestrial forms. Recent phylogenetic analyses suggest that the sister taxon to Crocodylomorpha was a group of large-bodied predators known as “rauisuchians.” This juxtaposition produces a large morphological gap between early crocodylomorphs and their closest relatives. Here we present a new archosaur from the Upper Triassic Chatham Group of North Carolina, displaying a mosaic of loricatan characters, as well as unexpected features such as a bifurcated posterior process of the jugal (typically found in dinosaurs) and ornamentation on nearly all cranial elements. The specimen (NCSM 21588) is represented by a partial skull (estimated length > 50 cm) and several postcranial elements, suggesting that it is one of the largest Triassic crocodylomorphs discovered to date. Our phylogenetic analysis of 61 archosauromorphs and 412 characters (1775 MPTs, 1145 steps) recovers NCSM 21588 as one of the basal-most crocodylomorphs. The novel combination of skeletal characteristics shared with other Triassic carnivores, elongate and gracile skull shape of NCSM 21588, and unusually large body size documents an unexpected step in Late Triassic paracrocodylomorph evolution. The Carnian age of the lower Chatham Group suggests that not only is NCSM 21588 among the oldest crocodylomorphs, it is also one of the earliest records of cranial ornamentation in the clade. In recent years, the lower Chatham Group has produced several new loricatan species including: NCSM 21588; an undescribed crocodylomorph with a nearly complete, articulated skeleton; Dromicosuchus grallator; and Postosuchus alisonae. These discoveries are essential to our understanding of the origin, early diversity, and morphological disparity of early Crocodylomorpha and highlight a need for greater sampling. However, the lack of a robust basin-wide correlation within the Deep River Basin is a persistent problem that is hindering study of fine scale evolutionary patterns and broader geochronology within the Newark Supergroup.