Meeting Abstract
Despite decades of research on lizard locomotion, the mechanics of the elbow joint and its relationship to manus orientation remain understudied. Previous studies on monitor lizards have inferred from dissection and X-ray cine that manus pronation is dictated by long-axis rotation of both the radius and ulna relative to the humerus. To further explore the kinematics of the lizard elbow, we use XROMM (X-ray Reconstruction of Moving Morphology) to characterize elbow movements in the central bearded dragon, Pogona vitticeps. Our results show that during stance, the radius and ulna both rotate laterally on their long-axes relative to the humerus, especially during elbow flexion. Given that the radial and ulnar condyles of the humerus have different morphologies, the antebrachial bones follow different paths at the elbow, resulting in their distal ends moving in opposite directions. These movements of the radius and ulna maintain palmar contact of the manus with the ground during stance in what can be described as the squamate equivalent of pronation. At the end of stance, the long-axis rotations of the radius and ulna reverse, rotating medially relative to the humerus, allowing the manus to supinate.. We find it significant that manus pronation is maintained in part through movements of the radius and ulna (lateral long axis rotation) typically associated with supination in birds and (at least for the radius) in mammals. Our data suggest that more examples of elbow kinematics across reptiles and mammals are needed to enhance our understanding of the ancestral mechanism for amniote pronation and supination.
