Vertical climbing, a behavior frequently performed by extant hominoids and atelines, has figured prominently in theories of locomotor evolution in the hominoids and hominins. For example, it has been proposed that vertical climbing pre-adapted hominins for bipedality. However, whether Pliocene hominins or Miocene hominoids practiced vertical climbing is still a subject of debate. Kinematic work on wild chimpanzees in Kibale National Park, Uganda has shown that vertical climbing requires extreme foot dorsiflexion, coupled with foot inversion and abduction. It is thus hypothesized that the morphology of the ankle, or talocrural joint, in vertical climbing Old World anthropoids is (1) adapted for positions of extreme dorsiflexion, inversion, and abduction, and (2) adapted to withstand the forces incurred on the joint while being loaded in these foot positions. This project will examine the external and internal morphology of the ankle in thirteen species of living primates, including humans, to test whether vertical climbers have a distinct talocrural joint morphology. External morphology of the talocrural joint will be assessed using linear and angular properties of the tibia and talus. Furthermore, the complex shape of the ankle will be modeled using data obtained from 3D laser scans. The role of ankle ligaments in restricting joint motion and stabilizing the ankle will be determined by quantifying the specific location and shape of the bony attachments. Finally, the internal morphology of the talus will be examined using CT scans of modern anthropoid tali. To address whether extinct hominoids and hominins included vertical climbing in their locomotor repertoire, results obtained from the study of modern ankles will be applied to fossil tibia and tali, including CT scan data obtained from seven hominin tali from fossil localities in South Africa.
This project examines the ankle joint across a wide range of modern primates to help reconstruct the locomotion of extinct apes and humans, and test whether early human ancestors were capable tree climbers. This project focuses specifically on the ankle joint to test whether the remarkable tree climbing ability of modern apes has a deep history, and whether vertical tree climbing may have been a precursor to human bipedality. Because the ankle joint is so often injured in modern humans, this study will also track the evolutionary history of ankle ligaments using fossil tibia and tali to determine the timing of and circumstances leading to our modern ankle anatomy.
