WILLEY, J.S.*; BLOB, R.W.; Clemson University, SC: Tail function during aquatic walking in snapping turtles
Most lineages of quadrupedal reptiles (e.g., lizards, crocodilians) possess long tails that play important roles during locomotion on land (as the origin for caudofemoralis, a major leg retractor muscle) and in water (as a propagator of propulsive waves during swimming). Long tails are ancestral among turtles, but most extant species have highly reduced tails that likely contribute little to propulsive forces. Tails of chelydrids (snapping turtles), however, are unusually long and robust among extant groups, and have been shown to help stabilize juveniles climbing slopes on land. Chelydrids typically traverse aquatic habitats by walking along pond or stream bottoms rather than swimming. If the tail contributes to propulsion during aquatic walking in chelydrids, it might show flexion coordinated with limb retraction (similar to terrestrial walking), or flexion and wave propagation independent from limb retraction (similar to swimming in other reptiles). To evaluate the role of the tail in chelydrid propulsion, we collected digital video of tail kinematics from common snapping turtles (Chelydra serpentina) during aquatic walking. Within strides, low-amplitude traveling waves originate at the base of the tail and travel posteriorly. The tail base (first caudal vertebra to vent) flexes 16 � 3° to each side, similar to the flexion range of swimming alligators and suggesting the tail may generate propulsive thrust. However, tail flexion toward the retracting hindlimb begins at 86 � 2% of the stride cycle (75% of stance), after hindlimb retraction has largely ceased. This suggests tail flexion and hindlimb retraction are controlled independently, perhaps indicating that caudofemoral muscles (with reduced caudal attachment in turtles) serve only as limb retractors, whereas tail flexion is produced by caudal, pubo- and ischiococcygeus muscles.
