A new suchian archosaur from the Upper Triassic of North Carolina

Abstract

ABSTRACT A partial but largely articulated skeleton of a ‘rauisuchian’ archosaur from Late Upper Triassic strata of the Durham sub-basin, Deep River basin, Newark Supergroup, North Carolina, represents a new species of Postosuchus Chatterjee, 1985. It represents the first record of this taxon from eastern North America. The well preserved specimen includes cranial bones, a largely articulated right manus, right and left pedes, pubes, axis, several postaxial cervical, dorsal, and caudal vertebrae, chevron bones, osteoderms, interclavicle, clavicles, cervical ribs, a sacral rib, and a complete set of gastralia. The skeletal elements are described and compared to those of other ‘rauisuchians’. An apparant autapomorphy of Postosuchus alisonae includes a well developed flange on the proximal portion of metacarpal II fitting into strongly proximally grooved metacarpal I. The new specimen includes many bones previously unknown for Postosuchus and it allows a more complete differentiation of Postosuchus from other ‘rauisuchian’ genera. Diagnostic features of this genus include an axis with two ventral keels; postaxial cervical centra with strongly developed single ventral keels that are anteriorly and/or posteriorly extended into hypapophyses; short ribs on the anterior cervical vertebrae; heart-shaped cervical neural ‘spine tables’; a subrectangular, relatively short coracoid; and proportionately short manus with dorsoventrally compressed, reduced, blunt unguals on manual digits III and IV. Morphological comparisons indicate a close relationship between Postosuchus and Batrachotomus and possibly also Tikisuchus.