1Evolutionary Anthropology, Duke University, 2Division of Anatomy, University of Alberta
Friday 8:15-8:30, Galleria North
Primates and other mammals display remarkable diversity in limb design (length, mass, and weight distribution), which has profound implications for how limbs move during locomotion. While many studies have focused on stance phase mechanics, swing phase has been overlooked. The rate of swing and required muscular effort, which are influenced by pendulum length and mass, can affect energetic costs and speed. It is assumed that as speed increases stance period decreases, while swing period stays relatively constant. In effect, limb inertial properties may constrain the swing period, which is especially relevant for primates as prehensile hands and feet may contribute to heavier limbs more distally. By calculating swing period in three carnivorans and a wide range of primate species, we test the hypotheses that: (1) swing phase period stays constant as speed increases, and (2) primates have relatively longer swing periods compared to other mammals. Results from our sample show that stance period decreases as speed increases, while swing period remains nearly constant in each species examined. Lemurs and kinkajous had relatively longer swing periods compared to cats, while Saimiri had relatively short swing periods compared to other primates. These data suggest that swing phase period is constrained by limb design and that in some arboreal mammals, the need for decreasing swing period must be balanced by other factors such as longer limbs and more distally positioned musculature. These competing factors must be understood for accurate interpretations of limb anatomy in living and fossil mammals.
Supported by NSF BCS 9904401and 0452217