A new specimen ofHesperosuchus agilisfrom the Upper Triassic of New Mexico and the interrelationships of basal crocodylomorph archosaurs

An articulated partial skeleton, including a nearly complete skull and left forelimb, of a crocodylomorph reptile from the Upper Triassic Chinle Formation of Ghost Ranch, New Mexico, is referable to Hesperosuchus agilis Colbert, 1952. It contributes much new information on the skeletal structure of this previously poorly known taxon. A large, circular palpebral bone is present in each orbit. The quadratojugal is particularly well preserved and suggests a reinterpretation of this element in related taxa including Sphenosuchus. Previous analyses of sphenosuchian relationships reached conflicting results, and a critical review of the characters used in these analyses is presented. A phylogenetic analysis of basal crocodylomorph taxa provides weak support for sphenosuchian monophyly, placing Hesperosuchus with Saltoposuchus, Dibothrosuchus, and Sphenosuchus.