The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)


Limb excursion patterns of an arboreal marsupial (Petaurus breviceps) vary with substrate size and inclination

AMBER N. HEARD-BOOTH1, LIZA J. SHAPIRO1 and JESSE W. YOUNG2.

1Department of Anthropology, University of Texas at Austin, 2Department of Anatomy & Neurobiology, Northeast Ohio Medical University (NEOMED)

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Primate quadrupedalism is characterized by a variety of kinematic features not commonly observed among non-primate mammals. Convergent use of this locomotor strategy by arboreal marsupials is consistent with the hypothesis that movement within a complex arboreal milieu is the selective factor shaping primate quadrupedal kinematics. Recent studies have demonstrated that variation in substrate type and inclination influence primate kinematics, but arboreal marsupials are rarely examined with respect to these parameters, especially simultaneously. Here, we investigate the effect of substrate size and inclination on limb excursion and flexion in four adult sugar gliders (Petaurus breviceps), a small arboreal marsupial with grasping hands and feet. Compared to locomotion on horizontal substrates, walking up a 30° incline caused sugar gliders to reduce limb protraction angles at touchdown and increase limb retraction angles at liftoff. As substrate size decreased, sugar gliders increased knee extension, forelimb protraction and hind-limb retraction, irrespective of substrate inclination. The observed changes in limb excursion patterns in response to inclined substrates are similar to those documented for primates, despite sugar gliders’ preference for lateral-sequence gaits. The combination of lateral-sequence gaits with increased forelimb protraction complicates previous associations between diagonal-sequence gaits and use of large forelimb protraction angles in primates. Finally, use of extended knee postures on the smallest substrates was unexpected, and suggests that grasping may mitigate the need to lower the body’s center of mass to maintain balance.

Supported by NSF BCS 0647402 and UT Austin.

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