Meeting Abstract
The Gansfontein paleosurface (Mid-Permian, South Africa) preserves several footprints, including a trackway attributed to a single dinocephalian (a lineage of non-mammalian therapsids). In contrast to the straight digital axis indicated by articulated hands and feet of dinocephalians, digit impressions in this trackway are curved, with tips directed toward the trackway midline. To evaluate how such curved-digit prints were produced, we constructed contour maps to measure how the depth of an impression varied within individual prints. We poured milk into prints in successive increments of 2 mm in height, and traced the perimeters of filled areas on translucent paper taped to the paleosurface. Contours show features consistent with outward rotation of the hand and foot during stance. For example, impressions of digit I are shallow, but impressions of digit V are deep. Lateral edges of digit IV impressions are also steeper than medial edges. Thus, depth asymmetry between or within digits shows deeper or steeper lateral edges, consistent with outward foot rotation. Finally, distal tips of digit impressions are among the shallowest portions of prints; however, local ’overdeepened’ depressions are present several centimeters from distal digit tips, indicating that the toes rotated out from their initial point of placement prior to lifting of the foot off the ground. Despite narrow spacing between left and right prints, the presence of foot rotation during stance supports osteological evidence that dinocephalians used sprawling, rather than parasagittal limb posture. Close spacing of prints likely resulted from lateral bending of the body and significant cranio-caudal limb excursion, rather than adduction of the limbs under the body.
