WUNDERLICH, R.E.*; SCHAUM, J.C.; KILKENNY, P.; SINOPOLI, M.C.: Hindlimb kinematics during bipedalism in Propithecus

Propithecus is one of only a few primates to habitually travel bipedally when on the ground, yet little attention has been given to this mechanically challenging aspect of their locomotion. Vertical clinging and leaping (VCL) in indrid primates has been of interest since Napier and Walker (1967) first defined the category of VCL. Quantitative examination of VCL among prosimian primates has identified hindlimb functional and morphological specializations unique to indrid locomotion (Walker, 1974; Gebo, 1993; Dagosto 1989; Demes 1995, 1996, 1991). We extend these studies to include kinematics of terrestrial bipedalism in indrids and compare indrid bipedalism to that of other primates. We examined hindlimb kinematics and plantar pressure in 6 Propithecus verreauxi moving bipedally at the Duke University Primate Center. Kinematic data were collected with video cameras at 45�, 90� and 180� to the path of travel and analyzed using Peak Performance 2-D software. Plantar pressure distribution was collected using an EMED-ST pressure platform. Propithecus achieve an aerial phase at relatively slow speeds, resulting in a saltatory type of bipedalism. They use high hip and knee excursions compared with other primates. This is consistent with their high proximal angular excursions during �thigh-powered� leaping. The indrid foot has been described as designed for grasping rather than leverage (Gebo, 1988; Demes 1996), however push-off from the ground necessitates some pedal leverage. Despite their 4th-digit pedal axis, Propithecus push off their 1st and 2nd digits like hominoids, suggesting a mechanical advantage to using the medial side of the foot during bipedalism. Further study should address morphological and energetic adaptations to this unique form of locomotion.