Meeting Abstract
The evolution of tetrapod locomotion is typically considered to progress from a sprawling gait with the limbs out to the side, as in salamanders, to an erect stance with the limbs underneath the body, as in birds and mammals. However, studies of crocodylians reveal that a derived, erect stance can revert to sprawling stance. Moles (Talpidae) are one of the most specialized fossorial mammals and assume a sprawling stance. Their short, broad humerus is oriented perpendicular to the sagittal plane of body, and its movement has been suggested to be the primary contributor to the production of force during digging. We investigated the kinematics of the humerus in Eastern moles (Scalopus aquaticus) during walking, lateral strokes, and scratching. Behavioral studies suggest that moles use these three movements extensively during tunnel building and patrolling. We implanted radiopaque markers into the humerii of Eastern moles and tracked the movements of the humerus using x-ray reconstruction of moving morphology (XROMM) during walking on a flat surface, doing lateral strokes in loose couscous, and scratching in compact couscous. We found that the humerus moved differently during these three movements. During walking the humerus rotated primarily in the transverse axis, presumably to increase stride length. In contrast, during lateral strokes and scratching, rotation mainly occurred along both the longitudinal and transverse axes. However, transverse axis rotation started at a larger angle during the lateral stroke than during scratching, indicating a more extended posture of forearm at the beginning of the burrowing cycle in the lateral stroke than in scratching. The physiological and mechanical mechanisms behind these kinematic differences will be the focus of future study.
