Shape variation in the talus and medial cuneiform of chimpanzees and bonobos

Sarah E. Friesen, Ryan P. Knigge, Tea Jashashvili, William E.H. Harcourt-Smith, Margaret J. Schoeninger, Matthew W. Tocheri

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


Objectives: Bonobos and chimpanzees do not differ from one another in overall frequencies of arboreality versus terrestriality as much as once thought. Thus, at a broad level, one would predict that there is little difference in foot morphology among Pan taxa. However, behavioral data suggest that bonobos more often use smaller diameter substrates (<10 cm) when climbing whereas western chimpanzees frequently climb larger diameter (>15 cm) substrates. This study tests the hypothesis that if Pan medial cuneiform and talus morphology reflects these substrate preferences, then the morphology of these bones should favor hallucial grasping in bonobos and an inverted foot set in western chimpanzees. Materials and Methods: Three-dimensional geometric morphometric (3DGM) methods were used to explore shape variation in 126 talus and 127 medial cuneiform 3D surface models acquired from 108 chimpanzees (24 western, four Nigeria-Cameroon, 33 central, 32 eastern, and 15 captive unknowns) and 22 bonobos. Results: The shapes of the talus and medial cuneiform in Pan covary as a functional unit emphasizing hallucial grasping with a less inverted foot set in bonobos and a more inverted foot set with a less abducted hallucial set in western chimpanzees. Other chimpanzee subspecies fall between these two extremes. Discussion: Bonobo and western chimpanzee medial cuneiform and talus shapes are consistent with their differing preferences for using smaller and larger diameter substrates, respectively, when vertically climbing. These results suggest that even among closely related taxa, foot, hand, and other postcranial anatomy may be fine-tuned for specific locomotor behaviors or preferences.

Original languageEnglish (US)
Article numbere24571
JournalAmerican Journal of Biological Anthropology
Issue number3
StatePublished - Mar 2024

Bibliographical note

Funding Information:
Ontario Ministry of Colleges and Training; Queen Elizabeth II Graduate Scholarship for Science and Technology; Canada Research Chairs Program; Social Sciences and Humanities Research Council of Canada, Grant/Award Number: 435‐2017‐1234; Wenner‐Gren Foundation, Grant/Award Number: 7822 Funding information

Funding Information:
This research was supported by a Wenner‐Gren Foundation post‐PhD grant (Grant Number 7822), the Social Sciences and Humanities Research Council of Canada (Insight Grant 435‐2017‐1234), and funds from the Canada Research Chairs Program (to MWT), as well as by a Joseph Armand Bombardier CGS M award from the Social Sciences and Humanities Research Council of Canada and a Queen Elizabeth II Graduate Scholarship for Science and Technology from the Ontario Ministry of Colleges and Training (to SEF). We would like to thank the following museums, institutions, and organizations for access to specimens: the Smithsonian Institution's National Museum of Natural History, the Royal Museum of Central Africa, the Academy of Natural Sciences of Drexel University, the American Museum of Natural History, the National Museums of Kenya, the Powell Cotton Museum, the University of Minnesota Evolutionary Anthropology Labs, the Max Planck Institute for Evolutionary Anthropology, and the Center for Academic Research and Training in Anthropogeny. For curatorial and other assistance, we thank Richard Thorington, Linda Gordon, Emmanuel Gilissen, Wim Wendelen, Ned Gilmore, Eileen Westwig, Ogeto Mwebi, Inbal Livne, Christophe Boesch, Jean‐Jacques Hublin, David Plotzki, and Zewdi Tsegai. Finally, MWT especially acknowledges his PhD advisor, Dr. Mary Marzke, for her mentorship, supervision, and training, as well as for inspiring the research conducted in this study.

Publisher Copyright:
© 2022 The Authors. American Journal of Biological Anthropology published by Wiley Periodicals LLC.


  • Pan paniscus
  • Pan troglodytes
  • climbing
  • functional morphology
  • tarsals


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