Another look at the anthropoid elbow

Abstract

Functional features of the articular surfaces of the joints of the elbow region are described for a number of extant and fossil anthropoids. At the humeroradial and proximal radioulnar joints of extant hominoids a complex of features occurs that guarantees stability throughout extensive pronation-supination movements. By contrast, in extant non-hominoids the morphology of these joints is such as to permit more limited movement and to provide a close-packed position in full pronation. Ramapithecines and Oreopithecus resemble extant hominoids in these features, while Proconsul exhibits some features of both groups of extant anthropoids. The other Oligocene and Miocene anthropoids investigated all resemble extant non-hominoids. Major differences in the humeroulnar joint relate mostly to different means of stabilizing the joint. In extant hominoids, Oreopithecus, and ramapithecines the joint is truly trochleiform and is stabilized against forces acting in any direction. In other Oligo-Miocene anthropoids except Proconsul, and in extant non-hominoids, the main joint surface is more cylindrical, and is stabilized by an anterodistally projecting flange medially and a posteriorly projecting flange laterally. These features are best developed in cercopithecoids. It is suggested that in cebids the humeroulnar joint is translatory, but that it is non-translatory in all the extant and fossil catarrhines considered. A number of autapomorphies in the elbow regions of hominoids and of cercopithecoids are tabulated and grouped in terms of their functional significance. On the basis of this distribution of features, and using Cebus as an out-group, it is suggested that Oreopithecus, ramapithecines, and Proconsul are hominoids. On the basis of the features examined, it is not possible to determine whether it is cercopithecoids or the taxon to which Dendropithecus and Pliopithecus belong that is the sister group of hominoids. Aegyptopithecus is the sister group of all other catarrhines.