The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

Strategies in below branch locomotion in non-specialized quadrupeds


Evolutionary Anthropology, Duke University

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The shift to specialized suspensory locomotion is interpreted as a major transition during the primate evolution. The ability to locomote both above and below branches has many potential benefits including balance and foraging, but presents challenges associated with safety and energy expenditure. There is limited data about which, if any, mechanical solutions animals use to meet these challenges. Here we explore the limb mechanics of above and below-branch locomotion in a relatively large-bodied primate (Varecia variegata). We test the hypotheses that during inverted quadrupedalism (1) the hands and feet remain above the substrate to provide security; (2) that the effective limb length (ELL) is greater than in above branch locomotion, thus requiring less muscular effort to support the body against gravity and providing longer limbs for swinging locomotion.

Video recordings of V. variegata (n=3) walking on a horizontal pole were digitized for hand, foot, shoulder and hip position throughout the stride. Contrary to our hypotheses, during inverted walking animals adopted more crouched (pulled-up) postures with shorter ELLs. This crouched movement may engender higher metabolic costs compared to above-branch walking. The pattern of hand and foot position throughout the stride is similar during both above- and below-branch locomotion:The foot remains on the same side of the substrate as the animal’s body, the hand on the opposite. This hand position maintains the ability to pull the hands and body towards the branch at any time. Conservation of gait between locomotor orientations may have been advantageous during the evolution of specialized suspensory locomotion.

This project was funded by the National Science Foundation's Graduate Research Fellowship Program (GRFP)

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