Meeting Abstract

P1.144  Tuesday, Jan. 4  The biomechanics of pillar-erect suchian archosaurs: convergence and disparity in bipedal archosaur locomotion SCHACHNER, ER*; SARRAZIN, JC; BATES, KT; University of Utah; University of Utah; University of Liverpool eschachner@gmail.com

Obligate bipedalism has independently evolved multiple times in many different vertebrate lineages. As a result the musculotendinous modifications associated with the skeletal changes accompanying this posture have received considerable attention in groups with a well-known fossil record. Like their dinosaurian relatives, multiple lineages of suchian archosaurs convergently evolved parasagittally erect limbs; however, basal archosaurian taxa developed a ventrally projecting acetabulum, in contrast to the laterally projecting hip of ornithodirans. The discovery of an articulated specimen of Poposaurus gracilis has provided the opportunity to generate the first phylogenetically-based reconstruction of pelvic and hindlimb musculature of a suchian archosaur, from which a 3D model of the musculotendinous system was used to predict individual muscle paths, lengths, and moment arms for a range of hindlimb postures. For comparative purposes, the muscle moment arms were also reconstructed for select phylogenetically relevant extinct and extant taxa with complete skeletons. Preliminary results suggest that Poposaurus had myological adaptations associated with the ‘pillar-erect’ hip and that the moment arms for hip adduction and both medial and lateral femoral rotation were much lower than those found for nonavian theropods. However, the majority of the muscle moment arms in Poposaurus were more similar to that of nonavian theropods than those found for the ostrich or the alligator.