Locomotor Anatomy and Behaviour in Olive Baboons: Integrative Analysis from Early Infancy to Autonomy

Overview & Synopsis

The diversity of the environments in which baboons live demands specific locomotor activities (e.g. endurance walking, cliff climbing, etc.). Hence locomotor capacities and the development thereof are key to their survival. To improve our understanding of these performances and how these relate to morphology and behaviour we studied an important period of the baboons’s development, i.e. the transition from the onset of independent foraging to autonomy (from 5 months to 2 years old). We conducted a longitudinal follow-up of six infant olive baboons living in captivity at the Primatology Station of the CNRS in France. We studied, in parallel, the morphometrics, the temporal kinematics and the positional behaviour of these individuals. In addition, we had the opportunity to analyse longitudinal morphometrics, collected over a seven-year period, on a large sample of captive olive baboons (30 individuals) including the male and female parents of our infants. This enabled us to describe the full morphological development of this species and to embed our sample in a larger developmental frame. Furthermore, with regard to questions on the origin of human bipedalism and the relevance of primate models, we also analysed behavioural data on bipedalism collected on a cross-sectional and ontogenetic sample of 22 baboons belonging to the same captive population. First, our results show that the proportion of quadrupedal walking gradually increases on the expense of grasping behaviours during infancy. We observed that this pattern is highly correlated to changes in the body mass distribution, mainly at the level of the limbs where mass shifts proximally. While a more distal limb mass distribution reflects important grasping capacity for clinging onto the mother’s fur, more proximal masses into the limbs are adaptive for reducing energy consumption during quadrupedal locomotion. Second, our results show that the ontogenetic changes in the pattern of body mass distribution influence bipedal walking in juveniles and adults in terms of bout duration, i.e. in individuals that possess a lighter head on a heavier trunk show longer bipedal bouts. Third, during the early period of development, young baboons improve their interlimb coordination in quadrupedal walking. We found that the intrinsic morpho-dynamics of fore- and hind limbs (at the level of the convergence of the natural pendular period) have a significant and positive impact on this interlimb coordination pattern, thus probably facilitating, very early in development, the motor control and learning of quadrupedal walking. Finally, baboons occasionally walk spontaneously in a bipedal way and our results show that there is an improvement of the coordination of the hind limbs in this posture, coinciding to the development of interlimb coordination in quadrupedal walking. Hence, improvement of quadrupedal locomotor capacity does not exclude the development of bipedal behaviours, despite bipedal experiences remain rare in the ontogeny of baboons (