Footfall patterns, stride length and speed of vertical climbing in spider monkeys (Ateles fusciceps robustus) and woolly monkeys (Lagothrix lagotricha).

Vertical climbing is central to theories surrounding the locomotor specialisations of large primates. In this paper, we present spatiotemporal gait parameters obtained from video recordings of captive spider monkeys (Ateles fusciceps robustus) and woolly monkeys (Lagothrix lagotricha) in semi-natural enclosures, with the aim of discovering the influence of body weight and differences in general locomotor behaviour on vertical climbing kinematics on various substrates. Results show that there are only few differences between gait parameters of climbing on thin trees, vertical and oblique ropes, while climbing on large-diameter trees differs considerably, reflecting the higher costs of locomotion on the latter. At the same speed, Ateles takes longer strides and the support phase takes a smaller percentage of cycle duration than in Lagothrix. Footfall patterns are more diverse in Ateles and include a higher proportion of ipsilateral limb coupling. Compared to other primates, the gait characteristics of vertical climbing of atelines most closely resemble those of African apes.