Hindlimb biomechanics of the early dinosaur relative Lagosuchus lilloensis

ALEJANDRO OTERO; PETER BISHOP; JOHN HUTCHINSON

Congreso; International Congress of Vertebrate Morphology; 2023

The Late Triassic archosaur Lagosuchus lilloensis (= Marasuchus) occupies a pivotal phylogenetic position in between early cousinsoutgroups to dinosaurs (e.g., pterosaurs) and true dinosaurs. Indeed, it is close to expectations for the general form and function of an ancestral dinosaur, such as having long hindlimbs and presumably a bipedal stance. It thus it has long been seen as pivotal for understanding the origin and early evolution of Dinosauria. However, the functional consequences of its osteology have only been studied qualitatively. We micro-CT scanned all known specimens in Argentina and reconstructed a 3D digital composite skeleton from the best-preserved bones. In this process, we identified some bones that do not pertain to this taxon, and others that resolve or contribute to controversies regarding what bones belong to itits anatomy. We used the digital model in biomechanics software to reconstruct the hindlimb musculature and the body shape (e.g., centre of mass). Using biomechanical simulation, we then analyse how it well it ran , and compare these results to those of others for bipedal early archosaurs. Our findings illuminate how the dinosauriform Lagosuchus lilloensis may have moved, and contribute to debates over if, or how, locomotor function impacted the survival of dinosaurs vs. other taxa across the Triassic-Jurassic mass extinction.