Ecological divergence and talar morphology in gorillas

Authors

  • Rachel H. Dunn,

    1. Department of Anatomy, Des Moines University, Des Moines, IA
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    • Rachel H. Dunn and Matthew W. Tocheri contributed equally to this work.

  • Matthew W. Tocheri,

    Corresponding author
    1. Human Origins Program, Department of Anthropology, National Museum of Natural History, Smithsonian Institution, Washington, DC
    2. Center for the Advanced Study of Hominid Paleobiology, Department of Anthropology, The George Washington University, Washington, DC
    • Correspondence to: Matthew Tocheri, Human Origins Program, Department of Anthropology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560 USA. E-mail: tocherim@si.edu

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    • Rachel H. Dunn and Matthew W. Tocheri contributed equally to this work.

  • Caley M. Orr,

    1. Department of Anatomy, Midwestern University, Downers Grove, IL
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  • William L. Jungers

    1. Department of Anatomical Sciences, Stony Brook University, Stony Brook, NY
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ABSTRACT

Gorillas occupy a variety of habitats from the west coast to eastern central Africa. These habitats differ considerably in altitude, which has a pronounced effect on forest ecology. Although all gorillas are obligate terrestrial knuckle-walking quadrupeds, those that live in lowland habitats eat fruits and climb more often than do those living in highland habitats. Here we test the hypothesis that gorilla talus morphology falls along a morphocline that tracks locomotor function related to a more inverted or everted foot set. This proposed morphocline predicts that gorillas living in lowland habitats may have a talocrural joint configured to facilitate a more medially oriented foot during climbing, suggesting that they may be more adaptively committed to arboreality than gorillas living in highland habitats. To quantify the relative set of the foot in gorillas, we chose two three-dimensional measurements of the talocrural joint: mediolateral curvature of the trochlea and relative surface area of the lateral malleolus. Our results show that, in comparison to their eastern counterparts, western gorillas have talar features that reflect a more medially directed sole of the foot. This morphology likely facilitates foot placement in a wider range of positions and minimization of shearing stresses across the joint when the foot is loaded on more curved or vertically oriented substrates as occurs during climbing and other arboreal behaviors. In contrast, eastern gorilla talar morphology is consistent with habitual placement of the foot with the sole directed more inferiorly, suggesting more effective loading during plantigrade push-off on terrestrial substrates. Am J Phys Anthropol 153:526–541, 2014. © 2013 Wiley Periodicals, Inc.

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