CLIMBING, BRACHIATION, AND TERRESTRIAL QUADRUPEDALISM - HISTORICAL PRECURSORS OF HOMINID BIPEDALISM

The vertical-climbing account of the evolution of locomotor behavior a nd morphology in hominid ancestry is reexamined in light-of recent beh avioral, anatomical, and paleontological findings and a more firmly es tablished phylogeny for the living apes. The behavioral record shows t hat African apes, when arboreal, are good vertical climbers, and that locomotion during traveling best separates the living apes into brachi ators (gibbons), scrambling/climbing/brachiators (orangutans), and ter restrial quadrupeds (gorillas and chimpanzees), The paleontological re cord documents frequent climbing as an ancestral catarrhine ability, w hile a reassessment of the morphology of the torso and forelimb in liv ing apes and Atelini suggests that their shared unique morphological p attern is best explained by brachiation and forelimb suspensory positi onal behavior. Further, evidence from the hand and foot points to a te rrestrial quadrupedal phase in hominoid evolution prior to the adoptio n of bipedalism. The evolution of positional behavior from early homin oids to hominids appears to have begun with an arboreal quadrupedal-cl imbing phase and proceeded though an orthograde, brachiating, forelimb -suspensory phase, which was in turn followed by arboreal and terrestr ial quadrupedal phases prior to the advent of hominid bipedality. The thesis that protohominids climbed down from the trees to become terres trial bipeds needs to-be reexamined in light of a potentially long his tory of terrestriality in the ancestral protohominid. (C) 1996 Wiley-L iss, Inc.