Meeting Abstract
It is well-known that among terrestrial animals with parasagittal limb postures, center of mass (CoM) potential and kinetic energies fluctuate out-of-phase when walking, but fluctuate in-phase during running. Lizards move with a sprawled limb posture, and many are capable of running quadrupedally and bipedally. An earlier study on quadrupedal lizards revealed that despite their sprawled limb postures, their center of mass dynamics also follow an inverted pendulum model when walking, and a spring-mass model when running. However, bipedal locomotion in lizards is both kinematically and kinetically distinct from quadrupedal locomotion. In the present study, we quantify the CoM dynamics of a bipedally-running lizard. Our previous studies show that bipedally running basilisks produce fore-aft and vertical forces similar in magnitude to that produced by other parasagittal runners, but much larger medio-laterally directed forces. We hypothesized that they would exhibit the spring-mass CoM dynamics similar to most other running animals, in spite of their sprawled-limb posture. However, as a result of the large medio-lateral force production, we also hypothesized that they would have higher fluctuations of medio-lateral kinetic energy. We collected kinematic and force data from five adult brown basilisks running across a track way (20 trials total) with an embedded six d.o.f. force plate, while filming two views with a high speed camera (500 fps). CoM dynamics were calculated from the measured vertical, medio-lateral, and fore-aft force. We found that while running, basilisks’ CoM kinetic and potential energies fluctuate in-phase, indicative of a spring-mass model style of running. Despite differences in stance and morphology, lizard bipedal running shows functional similarities to other parasagittal runners.
