期刊
JOURNAL OF HUMAN EVOLUTION
卷 53, 期 2, 页码 119-134出版社
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jhevol.2006.10.007
关键词
adduction; grasping; hallux; opposition; plesiadapiform; primate; primate origins; vertical clinging and leaping
A foot specialized for grasping small branches with a divergent opposable hallux (hallucal grasping) represents a key adaptive complex characterizing almost all arboreal non-human euprimates. Evolution of such grasping extremities probably allowed members of a lineage leading to the common ancestor of modern primates to access resources available in a small-branch niche, including angiosperm products and insects. A better understanding of the mechanisms by which euprimates use their feet to grasp will help clarify the functional significance of morphological differences between the euprimate grasp complex and features representing specialized grasping in other distantly related groups (e.g., marsupials and carnivorans) and in closely related fossil taxa (e.g., plesiadapiforms). In particular, among specialized graspers euprimates are uniquely characterized by a large peroneal process on the base of the first metatarsal, but the functional significance of this trait is poorly understood. We tested the hypothesis that the large size of the peroneal process corresponds to the pull of the attaching peroneus longus muscle recruited to adduct the hallux during grasping. Using telemetered electromyography on three individuals of Varecia variegata and two of Eulemur rubri-venter, we found that peroneus longus does not generally exhibit activity consistent with an important function in hallucal grasping. Instead, extrinsic digital flexor muscles and, sometimes, the intrinsic adductor hallucis are active in ways that indicate a function in grasping with the hallux. Peroneus longus helps evert the foot and resists its inversion. We conclude that the large peroneal tuberosity that characterizes the hallucal metatarsal of prosimian euprimates does not correlate to powerful grasping with a divergent hallux in general, and cannot specifically be strongly linked to vertical clinging and climbing on small-diameter supports. Thus, the functional significance of this hallmark, euprimate feature remains to be determined. (C) 2007 Elsevier Ltd. All rights reserved.
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