Facultative Use of Large Accelerations for Bipedal Running in Lizards

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In amniotes, bipedal locomotion has evolved repeatedly in various lineages. In many instances, a bipedal running posture evolved from a quadrupedal ancestor. The vast majority of lizard species are quadrupedal, yet many often employ a bipedal locomotor posture for several strides at the start, or during, a sprint. Numerous studies have tested hypotheses regarding why lizards may use a bipedal posture, yet its functional basis remains elusive. At least two hypotheses exist for why facultative bipedalism exists. One hypothesis suggests that it is a byproduct of high accelerations generated by the hind limbs at the start of a run, while another suggests that bipedal posture is used to overcome obstacles. These hypotheses are not mutually exclusive as high accelerations would be likely needed to transition from quadrupedal to bipedal running. Here we will present data comparing quadrupedal and bipedal postures of lizards while sprinting toward a single obstacle. Velocity and acceleration data were collected for each step during the lizard’s locomotion toward the obstacle. The data show that lizards can take several quadrupedal steps before transitioning to bipedalism, and that acceleration is highest on either the last quadrupedal, or the first bipedal, step. Hence, high accelerations are involved, but they do not always occur during the initial steps. This finding implies that the use of a bipedal posture is not only a spandrel of large accelerations, but rather, an individual may control when, or how, to use this posture.


Society for Integrative and Comparative Biology Annual Meeting (SICB)


Austin, TX