Characteristics of vertical climbing in African apes

Abstract

The evolution of bipedalism is a key event in the transition from apes to early hominids. Vertical climbing has been proposed to be the critical locomotor behaviour preadaptive to habitual bipedalism, although quantitative data about vertical climbing in nonhuman primates are scarce. This study focuses on 3D-kinematics of vertical climbing in different hominoid species in zoos. Emphasis is laid on a sufficient number of individuals and trials to guarantee the reliability of the results. The climbing sequences were recorded simultaneously by four digital video cameras at a speed of 50 frames/second. As direct contact with apes in zoos is not feasible, markerless kinematic analysis with subsequent manual digitisation of the joint centres was applied. In this paper, the method is described and data from 97 climbing sequences of five western lowland gorillas (Gorilla gorilla gorilla) in the Zurich Zoo (CH) are compared with data from 127 climbing sequences of nine bonobos (Pan paniscus) in Apenheul Primate Park (NL). Although African apes are similar in their postcranial anatomy, substantial differences in spatio-temporal gait parameters and kinematics of vertical climbing can be observed between gorillas and bonobos. The climbing of bonobos is more diverse in speed and gait patterns compared to gorillas and the duty factor is generally lower. A better understanding of the relationship between morphology and function in living apes will help to reconstruct the locomotor habits of fossil hominoids and early humans.