Ontogenetic changes in the body plan of the sauropodomorph Mussaurus and their implications for locomotion

ANDREW CUFF; ALEJANDRO OTERO; VIVIAN ALLEN; KRIJIN MICHEL; LAUREN SUMNER; DIEGO POL; JOHN HUTCHINSON

San Francisco

Congreso; Annual Meeting Society for Comparative and Integrative Biology; 2018

Society for Comparative and Integrative Biology

Mussaurus patagonicus is a sauropodomorph from the Early Jurassic of Argentina, originally described from hatchling remains. Further discoveries of juvenile and mature specimens provide a sufficiently complete series to reconstruct general patterns of ontogeny. Here, one each of hatchling, juvenile (~1 year old), and adult (8+ years old) individuals was studied. Digital models of the bones were created for each specimen, from segmented μ-CT scans for the smaller bones and photogrammetry and laser scans for the larger bones. Modelled bones were then articulated to produce complete skeletons, with missing bones being replaced by scaled versions of adults or closely related taxa. Each skeleton was wrapped in convex hulls and more anatomically realistic shapes, which were used to estimate body mass and centre of mass, and to conduct sensitivity analyses of these calculations. Our results show that Mussaurus rapidly grew from about 50g at hatching, to ~7kg at one year old, and reaching ~1540kg at adulthood. During this time the body?s centre of mass moved from a position in the mid-thorax to a more caudal position nearer the pelvis, consistent with a shift from quadrupedalism to bipedalism that might have occurred early in ontogeny in Mussaurus and other early sauropodomorphs. Our findings offer important new insights into the evolution of locomotion across Sauropodomorpha; consistent with a heterochronic shift to quadrupedalism near Sauropoda.