Kinematics of the cercopithecine foot on arboreal and terrestrial substrates with implications for the interpretation of hominid terrestrial adaptations.

The stereotyped characterizations of quadrupedal foot postures were tested by examining the kinematics of the cercopithecine foot on arboreal and terrestrial supports. Strictly arboreal species were compared with semi-terrestrial species for Cercopithecus, Cercocebus, Lophocebus, and Papio, in semi-natural or experimental settings. Results indicate that the kinematics of the cercopithecine arboreal quadruped differ in degree from stereotypical expectations for an arboreal quadruped. The relatively extended, adducted limb movements of the cercopithecines and the emphasis on the central digit as the functional axis of the foot suggest convergence with terrestrial mammalian cursors, and differ from the platyrrhine or colobine arboreal quadruped. The characteristics of the quadrupedal terrestrial primate foot contrast with the very unique pattern seen in the hominid foot. These contrasts provide a new perspective from which to interpret the hominid adaptation, in which the functional axis has remained fixed between the first and second digits. This pattern differs from virtually all other terrestrial mammals. The influence of bipedalism on this functional pattern is examined.