Meeting Abstract
During the course of vertebrate evolution, multiple tetrapod lineages evolved from sprawled to erect postures. While most studies have focused on the kinetics of quadrupedal and bipedal locomotion using an upright stance, far fewer have examined sprawled locomotion. Sprawled postures have classically been associated with greater bending forces on proximal limb segments (e.g., turtles, iguanas, and alligators) and increased energetic cost. Interestingly, the production of medio-lateral forces associated with the sprawled posture has also credited for increasing stability and maneuverability (e.g., cockroaches and geckos). Yet, for erect bipedal systems, the role of medio-lateral forces are often considered negligible; nothing is known about medio-lateral force production in sprawled bipedal runners. The goal of this study was to quantify the forces being produced during bipedal running in a sprawled locomotor system. The basilisk lizard is an appropriate model system because they are one of the few vertebrates that exhibit a sprawled posture and bipedal running. For this study, we ran 12 basilisks on a trackway with an embedded 6 d.o.f. force plate (ATI Mini-40) while filming two views with a high speed camera (500 fps). On average lizards ran at 1.8 ± 0.2 m/s. Initial results show that vertical force was characterized by a large initial impact force spike followed by a more gradual force development. Excluding the impact force spike, peak vertical force was 2.3 ± 0.3 body weight [BW] and peaked coincident with maximum fore-aft force (0.9 ± 0.2 BW). Medio-lateral forces were variable (0.7 ± 0.3 BW), suggesting that these forces could be important for locomotor stabilization, or may be an outcome of the sprawled posture. Comparisons will be made with other sprawled and upright animal systems that run bipedally or quadrupedally.
