METATARSOPHALANGEAL JOINT FUNCTION AND POSITIONAL BEHAVIOR IN AUSTRALOPITHECUS-AFARENSIS

Recent discussions of the pedal morphology of Australopithecus afarens is have led to conflicting interpretations of australopithecine locomo tor behavior. We report the results of a study using computer aided de sign (CAD) software that provides a quantitative assessment of the fun ctional morphology of australopithecine metatarsophalangeal joints. Th e sample includes A. afarensis, Homo sapiens, Pan troglodytes, Gorilla gorilla, and Pongo pygmaeus. Angular measurements of the articular su rfaces relative to the long axes of the metatarsals and phalanges were taken to determine whether the articular surfaces are plantarly or do rsally oriented. Humans have the most dorsally oriented articular surf aces of the proximal pedal phalanges. This trait appears to be functio nally associated with dorsiflexion during bipedal stride. Pongo has th e most plantarly oriented articular surfaces of the proximal pedal pha langes, probably reflecting an emphasis on plantarflexion in arboreal positional behaviors, while the African hominoids are intermediate bet ween Pongo and Homo for this characteristic. A. afarensis falls midway between the African apes and humans. Results from an analysis of meta tarsal heads are inconclusive with regard to the functional morphology of A. afarensis. Overall, the results are consistent with other evide nce indicating that A. afarensis was a capable climber. (C) 1994 Wiley -Liss, Inc.