Meeting Abstract

P3.54  Jan. 6  Mechanics of Bipedal and Quadrupedal Running in the Desert Iguana LACOUNT, L.T.*; BOROK, M.J.; AHN, A.N.; Harvey Mudd College; Harvey Mudd College; Harvey Mudd College aahn@hmc.edu

Desert iguanas (Dipsosaurus dorsalis) have the relatively rare ability to run well both bipedally and quadrupedally. However, the reason why lizards sometimes run bipedally is still uncertain. Lizards may have evolved bipedal locomotion as a means of escape (Snyder, 1952; Irschick and Jayne 1999). To test the hypothesis that lizards run bipedally to increase acceleration during escape (Aerts, et al., 2003), we examined these animals as they ran across a miniature force platform embedded into a 2.2 x 0.16 m track while we recorded high-speed digital video images in lateral and dorsal views. All force platform experiments were performed at the Concord Field Station of Harvard University. On average, the lizards accelerated 110% more when running on two legs than on four legs, but the range of maximal running speeds when bipedal tended to be lower than when quadrupedal. Furthermore, preliminary experiments measuring metabolic rate during running on a motorized treadmill indicated that the energetic cost remained constant between bipedal and quadrupedal modes of locomotion in these animals. These results support our hypothesis to suggest that Desert Iguanas run bipedally primarily to increase acceleration, rather than to increase maximal running speed or to decrease the energetic cost of locomotion. This research was supported by the Howard Hughes Medical Institute.