Meeting Abstract
Knuckle-walking (KW) is a unique form of terrestrial locomotion utilized only by chimpanzees and gorillas among primates, wherein the dorsal aspect of the manual intermediate phalanges contact the substrate. Little quantitative data documenting the forces and motions involved in KW, or the frequency with which it is utilized over other hand postures, exist for African apes, making it is difficult to evaluate hypotheses regarding the evolution of this unique locomotor behavior. Here we present laboratory-based 3D kinematic and kinetic data of KW in two subadult chimpanzees (Pan troglodytes), as well as field-based kinematic descriptions of KW in wild mountain gorillas (Gorilla beringei beringei) at Bwindi Impenetrable National Park, Uganda and Volcanoes National Park, Rwanda. Initial data indicate that chimpanzee KW is characterized by a peak vertical force late in stance phase (~70–80%), and fore-aft forces that are largely braking, but are propulsive during the last 10–40% of stance phase. During stance phase the wrist underwent ~25° of flexion/extension which was largely confined to 0–20% and 80–100% of stance, and underwent a range of ulnar/radial deviation of 20–25°. Kinematic data of wild mountain gorillas indicate that though KW is the main hand posture utilized during terrestrial walking (~90% of steps), gorillas also utilize other hand postures, such as dorsal metacarpal weight bearing and fist walking. Together these data form the basis from which we can evaluate hypotheses of the origin of knuckle-walking. Funded by NSF grants SBE 0935321, 1606853, 1520221, Max Planck Society, and the Leakey Foundation.
