Meeting Abstract

119.5  Tuesday, Jan. 7 11:15  Lizards popping a wheelie: Bipedal running in Australian agamid lizards CLEMENTE, C. J.; University of Queensland c.clemente@uq.edu.au

Bipedal locomotion is widespread among various taxa. While the reasons for bipedal locomotion in other taxa vary from energetic advantages to reassignment of the forearms to other uses, within lizards reasons for bipedal locomotion are still unclear. Recent modeling studies suggest bipedalism in lizards may be a consequence of a caudal shift in the body centre of mass (BCOM), combined with quick busts of acceleration, together which cause a torque moment at the hip lifting up the front of the body. Lizards are essentially ‘popping a wheelie’. Some lizards appear to run bipedally sooner and for longer than might be expected from this simple model, and it has been suggested that these lizards have exploited the consequence of bipedal locomotion. However, it is unclear how common this exploitation is among lizards. Do some lizards try to run bipedally or do most simply run bipedally by accident? We examined morphological data for 78 species across the squamate phylogeny and show that a rearward shift in the BCOM is associated with bipedal lineages. We then examined strides from 10 species of Australian agamid lizards, and recorded acceleration during bipedal or quadrupedal locomotion. Five of the 10 species were capable of steady state bipedal locomotion. We estimated the empirical acceleration threshold for these species to switch between quadrupedal and bipedal locomotion using logistic regression and compared this to thresholds estimated from morphological parameters alone. With the exception of two species, lizards were able to run bipedally at lower than expected accelerations based on morphology, suggesting that kinematics have a significant influence on bipedalism. Together, these results suggest most agamids have exploited changes in BCOM to become bipedal, suggesting that bipedalism in this group may convey some advantage, though what this advantage is remains the subject for future investigations.