Ape-like locomotor adaptations in the radius of the stem catarrhine Pliobates shed light on hominoid evolution

The 11.6. Ma pliopithecoid <i>Pliobates</i> was initially misinterpreted as a stem hominoid owing to multiple apelike postcranial features. Using 3D geometric morphometrics, we compare its radial shape with that of extant and extinct catarrhines to make locomotor inferences. The round and beveled radial head of <i>Pliobates</i> resembles that of modern apes, which we interpret as functionally related to efficient forearm rotation. This contrasts with its more plesiomorphic distal radius and proximal ulna, suggesting that <i>Pliobates</i> was more adapted for climbing than forelimb-dominated suspension and unable to perform gibbon-like ricochetal brachiation. Our results illustrate the mosaic and stepwise evolution of the catarrhine elbow and support the view that an apelike proximal radial morphology evolved multiple times as a climbing rather than suspensory adaptation. This agrees with the possibility that several features of the hominoid elbow were originally selected for climbing and subsequently co-opted for suspensory locomotion.