Evolutionary Anthropology, Duke University
March 27, 2015 9:45, Grand Ballroom A/B
It has been suggested that the evolution of bimanual locomotion in primates was preceded by a shift to below-branch quadrupedalism for purposes of feeding and balance, yet little is known about the mechanics of limb use during below-branch walking. Recent studies in primates have demonstrated an increased reliance on the forelimb for support and propulsion during below-branch compared to above-branch quadrupedalism, but it remains unclear whether similar biomechanical patterns exist for all mammals that walk below branches or whether non-primate species adopt differing strategies. This study examines the kinetics of below-branch quadrupedalism in Varecia variegata, Propithecus coquereli, Lemur catta, Daubentonia madagascariensis, Pteropus vampyrus, and Choloepus hoffmanni. Animals walked below an instrumented arboreal runway, and values for peak vertical, braking, and propulsive forces as well fore-aft impulses were collected from each limb.
All primates sampled displayed a consistent limb-loading pattern in which both the peak propulsive and vertical forces were greater in the forelimbs (FL Ppk = 22.5% bw; FL Vpk = 81.1% bw) than the hindlimbs. Additionally, the forelimbs served a net propulsive role (0.023 bws), while the hindlimbs served in a braking capacity (-0.021 bws). Conversely, bats and sloths displayed little differences in loading between the forelimbs and hindlimbs. Bimanual locomotion is unique to Primates, and involves, by definition, a dominant role of the forelimb. Forelimb dominance during below-branch quadrupedalism may represent a significant change that enabled a shift to the use of forelimbs in tension, and the evolution of bimanual locomotion in Primates, but not in other mammals.
This research was funded by the Force and Motion Foundation and the NSF Graduate Research Fellowship Program