Sprawling Locomotion in the Lizard Sceloporus Clarkii: Quantitative Kinematics of a Walking Trot

Abstract

Although the hindlimb is widely considered to provide the propulsive force in lizard locomotion, no study to date has investigated the kinematic patterns of the lizard hindlimb during running for more than one stride for a single individual. The quantitative kinematics of the hindlimb, pelvis and backbone are described here for two individuals of the lizard Sceloporus clarkii using a fast walking trot on a treadmill moving at a constant speed of 0.833 m s-1. Pelvic rotation, femoral retraction, knee flexion and posterior movement of the foot all begin before the foot hits the substratum and, thus, there is a terminal portion of the swing phase during which the limb is retracting. Pelvic rotation (to the opposite side), femoral protraction and knee flexion all begin before the foot leaves the substratum. The foot, however, continues to move posteriorly into the early swing phase. Thus, limb retraction and protraction movements do not directly correlate with footfall phases. Axial bending involves a rough standing wave with two nodes, one centered on each limb girdle. In Sceloporus clarkii, the foot clearly remains lateral to the knee and, thus, has a more sprawling posture than that of any other vertebrate studied to date. Therefore, the generalization that the 'lacertilian' foot passes under the knee joint is no longer supported. The kinematics of sprawling locomotion in Sceloporus clarkii are compared and contrasted with the general understanding of lizard locomotion based on qualitative work to date. Comparisons with other tetrapods reveal a fundamental functional dichotomy in hindlimb retraction mechanics in salamanders and mammals versus lizards that may be related to a key morphological difference in the saurian caudifemoralis muscle.

A general locomotion control framework for multi-legged locomotors

“…Surprisingly, modulating the lateral phase lag only affects the static stability, while body speed is not correlated with the lateral phase lag. On the other hand, animals including myriapods [34] and quadrupedal lizards [20,52,53] have been observed to modulate the lateral phase lag as speed increases. In other words, in biological systems, the loss of static stability is compensated by a gain in speed while our findings indicate that speed is independent of lateral phase lag modulation.…”

“…However, previous experimental gait studies with lizards and myriapods [20,34] have found that modulation of lateral phase lag is associated with changes in lateral body undulation. For example, lizards increase the amplitude of their lateral body undulation during transitions from LS walking to trotting or even DS gaits [20,24,25,50,52,53]. Similarly, myriapods change their leg wave pattern (lateral phase lag) at high speed while simultaneously increasing lateral body undulation amplitude [34].…”