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Chimpanzee hand anatomy
Chimpanzee hand anatomy













naledi are dated to the Middle Pleistocene between 335 kya and 241 kya. 9 No arboreal primate has phalanges that are both short and curved it is an aberration that confounds conventional interpretation. First, the phalanges are relatively short, resulting in humanlike hand proportions. Such curvature would normally and unequivocally suggest an arboreal milieu 3, but there are at least two reasons to doubt such an inference for H. 9 The degree of phalangeal curvature is astounding, with an included angle (0) that far exceeds that of modern humans ( Figure 1). Upsetting this orthodoxy is the hand of Homo naledi, recovered from Rising Star Cave, South Africa, in 2013-14 and described in 2015. Phalangeal curvature is therefore widely viewed as a measure of arboreality among primates - it is a classic form-functional trait that informs our interpretations of behaviour and ecology in the fossil record 1-7 (but see Wallace et al. 1-3 Greater curvature is advantageous to arboreal primates because it dissipates forces and dampens recruitment of muscles during finger flexion, thus economising energetic costs and simultaneously lowering the risk of falling. For example, loading stresses from vertical climbing and suspensory locomotion can increase the curvature of primate finger bones (phalanges) during growth and development. Keywords: human evolution, locomotion, climbing, suspension, bone curvatureīone is a dynamic tissue, and repeated mechanical loading can induce changes to its density and angular curvature. Our results show that a large proportion of a vertical rock wall would compel crimp and slope hand positions during climbing - grips that could explain the extraordinary phalangeal curvature expressed by a Middle Pleistocene hominin, Homo naledi.We present the first three-dimensional photogrammetric analysis of a vertical rock surface climbed by a non-human primate, the chacma baboon (Papio ursinus).If such proportions are representative of vertical rock surfaces elsewhere, it may be sufficient to induce stress-mitigating curvature in the phalanges of primates. Here we use three-dimensional photogrammetry to show that 82-91% of the climbable surface would generate high forces on the flexor tendon pulley system and severely load the phalanges of baboons and H. This rock surface is an attractive model for estimating the probability of extreme mechanical loading on the phalanges of rock-climbing primates. The importance of climbing rock walls is attested by several populations of baboons, one of which uses a 7-m vertical surface to enter and exit Dronkvlei Cave, De Hoop Nature Reserve, South Africa. The recent discovery of extremely curved phalanges in a hominin, Homo naledi, is puzzling, for it suggests life in an arboreal milieu, or, alternatively, habitual climbing on vertical rock surfaces. Mechanical loading of finger bones (phalanges) can induce angular curvature, which benefits arboreal primates by dissipating forces and economising the recruitment of muscles during climbing. VIIEvolutionary Studies Institute, University of the Witwatersrand, Johannesburg, South Africa VISkeletal Biology Research Centre, School of Anthropology and Conservation, University of Kent, Canterbury, UK VDepartment of Anthropology University of Pennsylvania, Philadelphia, Pennsylvania, USA IVMammal Research Institute, University of Pretoria, Pretoria, South Africa

chimpanzee hand anatomy

IIICentre for the Exploration of the Deep Human Journey, University of the Witwatersrand, Johannesburg, South Africa IIDepartment of Archaeology, Simon Fraser University, Burnaby, British Columbia, Canada IDepartment of Anthropology, Dartmouth College, Hanover, New Hampshire, USA Syeda VI Jesse Casana I Bernhard Zipfel VII Jeremy M. Elliott II, III David Gaynor IV Austin C. Mechanical loading of primate fingers on vertical rock surfaces















Chimpanzee hand anatomy