Does Bipedalism Confer an Advantage to Lizards Sprinting Over Obstacles?

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Terrestrial animals evade predators and capture prey by running over uneven and highly variable terrain. Characterizing the mechanisms to traverse obstacles can clarify crucial aspects of how animals interact with their environment. Bipedal running may allow animals to move over obstacles faster relative to quadrupedal running or jumping. Evolving first as a consequence of acceleration, facultative bipedalism is known to be exploited in certain lizard lineages. However, the ecological advantages of bipedalism remain unclear. We tested the hypothesis that bipedalism is advantageous relative to quadrupedal running when traversing obstacles. Specifically, we quantified how sprint speed and kinematics changed when traversing an obstacle and if this varied with the use of a bipedal or quadrupedal posture. Data were quantified from high-speed video of four lizard species running down a 3m runway either with or without an obstacle. In general, bipedal obstacle negotiation was faster relative to quadrupedal strides. Furthermore, bipedal obstacle negotiation was equal to sprint speed attained on a flat surface. The tail was held at a depressed angle during obstacle negotiation, suggesting that tail function is essential in maintaining speed. We suggest that while bipedalism may not increase velocity on a level, straight trackway, it does confer a velocity advantage when negotiating difficult terrain by allowing the lizards to maintain a constant center of mass height, extending stride length, increasing efficiency, and allowing a line of sight beyond the obstacle.


Society for Integrative and Comparative Biology Annual Meeting (SICB)


New Orleans, LA