In What Manner Do Quadrupedal Primates Walk on Two Legs? Preliminary Results on Olive Baboons (Papio anubis)

Abstract

Olive baboons (Papio anubis) are typically described as highly specialized for quadrupedal locomotion. Yet, they regularly and spontaneously walk bipedally as well. In what manner do they do this, when compared to other primates and humans? This question is of interest with regard to the origin of bipedalism in hominids. As a first step in understanding bipedal locomotion in baboons, we here present novel kinematic data, achieved using a custom-built setup that allows to measure individual locomotor parameters in a population of 55-60 captive olive baboons housed at the Primatology Station of the National Centre for Scientific Research (CNRS, France) using a high-speed digital recording system (100 fps) and a walkway (Podium). Within our population, we observed bipedality mainly in infant and subadult individuals: we present the sagittal motion parameters that we collected on a sample of 10 males and females of ages between 6 months and 5.5 years. As far as angular trajectories of the trunk and the lower limb joints are concerned., olive baboons walk bipedally in a rather stereotyped, compliant manner with a semiplantigrade stance phase, a trunk that is slightly tilted forward and immobile forelimbs kept forward in a parasagittal plane. Some small variations can be depicted, especially in the younger individuals of the sample. Among other "quadrupedal" primates of which the bipedal locomotion has been kinematically analyzed, the kinematics of bipedal walking of Papio anubis more closely resembles those described in Macaca fuscata. In the broader framework of our study, numerous transversal and longitudinal analyses are in progress on data as varied as noninvasive anatomical investigations, kinematics, kinetics, and paedobarography.