A hominoid proximal humerus from the Early Miocene of Rusinga Island, Kenya

Abstract

Recently, an isolated proximal humerus of an early Miocene hominoid was discovered at Rusinga Island, Kenya. The precise taxonomic allocation of this specimen is currently problematic, but the fossil almost certainly belongs to either Dendropithecus macinnesi or Proconsul africanus. The humeral head is expanded above the greater tuberosity in the new fossil suggesting that this early Miocene hominoid possessed a relatively mobile shoulder joint for climbing as well as for postural and feeding activities, and that rapid protraction at the shoulder joint was not important. This proximal humeral morphology contrasts with that of Aegyptopithecus, but is quite similar to that of Pliopithecus. Among extant primates, a similar proximal humeral morphology occurs in several platyrrhines such as Alouatta, but living apes share several apparently derived features of the proximal humerus which are lacking in the Rusinga Island specimen.