Bipedal behaviour in olive baboons: infants versus adults in a captive environment.

The olive baboon is described as a committed quadrupedal primate. However, available data show that they actually use a variety of locomotor and postural modes. Bipedalism is observed occasionally but spontaneously in captivity and in the wild. As observed in other Catarrhini, immature baboons appear to be more bipedal than adults: this study aims to provide the necessary quantitative data to support this hypothesis, as none has been available so far. The locomotor and postural repertoire was quantified for two age classes: infants beginning to forage independently, and adults. Our results show that infants appear to have a wider repertoire than adults, and bipedal postures and locomotion in infants, although infrequent, appear to distinguish them clearly from adults. In captivity, behavioural context and morphology are the two main factors that could explain age-related positional differences, given a constant ecological context.