Locomotion: Primate locomotion: some problems in analysis and interpretation

Abstract
Anatomical features biomechanically related to man’s upright posture and gait are well defined. But uncertainty surrounds the evolutionary pathway leading to human bipedalism, partly because the anatomical nature of man’s immediate ancestors is unknown, and partly because it is sometimes difficult to define and interpret the biomechanical significance of unique constellations of features that obtain in postcranial remains of fossil hominoids. In the innominate bone of Australopithecus the expanded iliac blade gives some appearance of similarity to that of man and has frequently been taken as indicating that Australopithecus had acquired a bipedal posture and gait. Methods have been developed to define quantitatively those morphological features of the innominate bone that are functionally related to the force pattern impressed during locomotion. On the basis of multivariate comparison of these features with those of extant primate groups representing a wide range of function of the hind-limb, it has been shown: first that the australopithecine innominate bone is unique in form; secondly, that this bone is somewhat better adapted than is that of extant subhuman primates for weight transmission in a bipedal posture; thirdly, that because of a dorsal orientation of the iliac blade Australopithecus lacked the means of powerful abduction of the thigh. Thus, any bipedalism practised by this extinct genus must have been quite different from that characteristic of Homo sapiens . Evidence from, for example, the foot, shows that it is quite possible that Australopithecus may have used its hindlimb in some form of arboreal locomotion, in addition to possible terrestrial bipedalism (albeit of a non-human type). It is not known whether Australopithecus was, or could have been, an ancestor of man. Correspondingly, whether or not such compound use of the hindlimb could have been ancestral to the human type of bipedalism is indeterminate.