Meeting Abstract
Sauropods are characterized by exceptionally massive body size and highly derived appendicular morphologies. However, the rarity of cartilage preservation in the fossil record has hampered inferences on their locomotor biology, such as loading, range of motion, and muscular attachments. This study investigated the evolutionary and functional significance of pelvic and femoral cartilages in Diplodocoidea, a diverse and well-represented clade of sauropods. We digitized femora, pelves, and caudal vertebrae of 35 sauropod and outgroup taxa before estimating key transitions in cartilage morphology using ancestral state reconstruction of osteological correlates. Like other sauropods, the rugose femoral head growth plate indicates thickening of hyaline cartilage in the capital region. However, diplodocoids uniquely possess terminally flattened capital growth plates, which indicates a greater contribution of hyaline cartilage in forming the convex, functional femoral head. Moreover, the expanded metaphyseal shelves of diplodocoid femora suggests extensive contribution of fibrocartilage in constructing the ventral femoral head. Finally, rugosities on the postacetabular ilial rim, as well as dorsoventrally expanded transverse processes on the anterior caudal vertebrae, suggest that diplodocoids possessed massive postacetabular cartilages that expanded the ilial blade caudally, buttressed by the anterior caudal transverse processes. This novel interpretation of the pelvic skeleton challenges traditional anatomical reconstruction of the diplodocoid hindlimb, and suggest that the hips and tail are functionally integrated to allow diplodocoids to adopt a greater range of locomotor postures, potentially even tail-assisted bipedalism.
