New Mexico Geological Society Annual Spring Meeting — Abstracts

Two species of the unusual archosauromorph Trilophosaurus, T. buettneri Case and T. jacobsi Murry, are known from diverse localities in the Upper Triassic Chinle Group in southwestern USA. Both species likely occupied similar ecological niches, based on morphological similarities in the postcrania, which are essentially identical. Trilophosaurus occurrences in the Chinle Group are relatively rare, but individual sites are exceptionally rich, suggesting that Trilophosaurus lived in a different paleoenvironment than more typical Chinle vertebrates, which lived in or near streams (phytosaurus, metoposaurs) or on floodplains (aetosaurs, rauisuchians, and dinosaurs). Two potential interpretations are that Trilophosaurus was either an arboreal climber or a fossorial differ. However, the gross skeletal features of Trilophosaurus are not compatible with a fossorial mode of life: the limbs are too long and gracile, proximal transversely broadened. The intermittent study of Trilophosaurus has caused the theory of it being arboreal, originally proposed by Gregory, to receive little mention in subsequent studies. We reexamined the functional morphology of Trilophosaurus using a qualitative functional morphological analysis of the skeleton, a quantitation examination of claw curvature, and a quantitative examination of manus/trunk and pes/trunk ratios. Claw morphology of Trilophosaurus shows similarities to the arboreal drepanosaurs Drepanisosaurus and Megalancosaurus. Our analysis provides ample evidence to suggest that Trilophosaurus was arboreal. We reconstruct Trilophosaurus as using the less mobile forelimbs for anchoring itself, the powerfully built hindlimbs for propulsion, and the large tail for retaining balance.