Forces Acting on the Foot of the American Alligator (Alligator mississippiensis) During Pedal Anchoring

Abstract

This study was undertaken to explore the forces acting on the pes during pedal anchoring and to discern if pedal anchoring required the activation of the intrinsic pedal musculature. Replica feet equipped with strain gauges were moved over mud substrate, mimicking locomotion and pedal anchoring. Quantification of the substrate tracks demonstrated that they were similar to those made by freely moving Alligator, that the locomotor and pedal anchoring tracks were significantly different, and that the composition of the artificial feet significantly altered the tracks. Strain gauges revealed significantly different forces at different locations (e.g., digit vs. heel) on the pes and between locomotor and pedal anchoring motions. Collectively, the results of the present study demonstrate that the forces acting on the pes during pedal anchoring are different from those during locomotion. Furthermore, varying the composition of the feet used in this study demonstrated the importance of flexion at the metatarsal/phalangeal joints. Resistance to this flexion in living crocodylians requires active muscle contraction, meaning that pedal anchoring is an active, not passive, behavior. These results offer the first insights into the mechanics of pedal anchoring and demonstrate how technologies like 3D printing can be applied to established problems like fossil trackways.