Meeting Abstract
The bones of the tetrapod forearm have maintained a conservative pattern of relationships in the over 300 million years since their initial evolution. The radius and ulna have parallel shafts of roughly equal length that meet proximodistally short carpal bones. Despite extreme changes in the forelimb function (e.g., terrestrial locomotion, swimming, flying, manipulation), this general pattern has remained consistent. A Late Triassic drepanosaurian reptile exhibits a radical deviation from the stereotypical tetrapod pattern. Drepanosaurus is an enigmatic diapsid known from Italy and New Mexico. In this taxon, the forearm exhibits a broad, flattened, and crescent-shaped ulna that has its long-axis oriented perpendicular to that of the radius. The ulna distally contacts two slender carpals, which are proximodistally longer than the radius. The manus supports a gigantic, recurved claw that is longer and more massive than any other forelimb bone. Reconstruction of muscle attachment sites suggests substantial expansion of attachments for digital flexors and extensors, potentially a consequence of the massively expanded unguals.
