Department of Anthropology, Southern Illinois University Carbondale
Saturday 16, Park Concourse
Manual complexity in great apes is considered to be an important facet of hand evolution, reflective of advanced cognitive skills, and is likely influenced by morphological adaptations in hand shape related to suspensory lifestyles. Relatively little is known about the manual abilities of the small apes, but they are generally assumed to have limited manual complexity because of their highly specialized hands. This study examined manual skill during foraging in wild small apes (Hylobates lar) compared with similar-sized, sympatric monkeys (Macaca nemestrina) with a broadly similar dietary profile at Khao Yai National Park, Thailand, in order to directly test whether differing manual abilities facilitate access to more or different (higher quality) foods, and whether small apes demonstrate enhanced manual complexity when handling foods similar to that seen in great apes. Sixteen months of videotaped hand use were recorded for eight gibbon groups (16 animals) and one macaque troop (9 animals). Results show that gibbons have a larger manual repertoire for precision skill than macaques, gibbons demonstrate a unique form of previously undocumented hand-foot bimanual coordination during foraging, and their sophisticated feeding skills are directly related to greater wrist mobility in varying hand positions during feeding, especially in the terminal branches. These critical differences allow gibbons to be more selective in reaching and choosing foods than is possible for pronograde quadrupedal monkeys.