Meeting Abstract
Many lizards are capable of bipedal locomotion via high acceleration and/or posterior shift in body center of mass (BCoM). Kinematic analyses to date have focused primarily on the role of hindlimbs in generating power and acceleration. Yet forelimb position, which may affect a shift in BCoM, has yet to be studied in the context of bipedalism. This study quantified forelimb positions when transitioning to and from a bipedal posture at the start of a sprint and when crossing an obstacle. Change in BCoM from varying forelimb positions was also quantified. Two species with contrasting body forms (and thus different BCoM) were studied (Sceloporus woodi, Aspidoscelis sexlineata) to assess potential variation due to body plan and obstacle crossing behavior. Lizards were coerced to run along a 1.4-meter track with an obstacle present and filmed with high speed video. A subset of lizards was euthanized and BCoM was measured. Four commonly used forelimb positions were noted during bipedal running: gait cycle, cranial extension, cranial flexion and adduction, and caudal extension. When transitioning to a bipedal posture at an obstacle, S. woodi primarily held their forelimbs in a cranially flexed and adducted position. Caudal extension of the forelimbs was primarily used by A. sexlineata when transitioning to a bipedal posture. Both species primarily used a gait cycle when transitioning to a quadrupedal posture. Aspidoscelis sexlineata has a more posteriorly shifted BCoM (9.13mm ±0.78) than S. woodi (12.87mm ±0.55). Caudally extended forelimbs shifted the BCoM (0.66mm ±1.53) further posteriorly. Thus, forelimb position aids transitions between bipedal and quadrupedal posture by shifting the BCoM, and these patterns appear to be stereotyped for some species.
