SCHAUM, J.C.*; WUNDERLICH, R.E.; James Madison University: Hindlimb kinematics during bipedalism in Propithecus verreauxi

Bipedalism is rare in primates and has occurred in 2 distantly related groups, hominoids and indrids. Although copious data are available on the mechanics of bipedal locomotion in hominoids and vertical clinging and leaping (VCL) in indrids, no research has addressed the unique mode of bipedal locomotion exhibited by select indrid primates. Propithecus verreauxi is a highly specialized indrid vertical clinger and leaper that uses a peculiar form of bipedalism on the ground. The objectives of this study were to determine 1) whether traditional kinematic definitions (e.g. center of mass (COM) movement, duty factor) of walking, running, or galloping describe Propithecus bipedalism, 2) the influence of VCL specializations on the kinematic patterns and propulsion mechanisms used by Propithecus during bipedalism, and 3) whether kinematics of bipedal gaits in Propithecus are similar to bipedal gaits in other primates? Video was collected of 5 adult Propithecus verreauxi moving bipedally in a semi-natural setting at the Duke University Primate Center. Duty factor, footfall patterns, joint angles, and movement, velocity and acceleration of the COM were calculated in the sagittal plane for 73 steps. Propithecus uses a bipedal gallop, a unique occurrence of this form of locomotion among mammals. The kinematic similarities (e.g. large hip and knee angular excursions and preparatory countermovements) between bipedal galloping and VCL lead us to suggest that Propithecus takes advantage of specializations for VCL to conserve energy during bipedal galloping. Propithecus also walks bipedally at slower speeds. When Propithecus walks, they utilize a compliant gait similar to that of other primate facultative bipeds (Pan, Hylobates). During bipedal walking, energy conservation may be sacrificed for increased balance and reduced joint loads.