DUFF, C.M.; FISH, F.E.; West Chester University, Pennsylvania; West Chester University, Pennsylvania: Enhanced Propulsion Using Undulation of the Elongate Tail of the South American Giant River Otter (Pteronura brasiliensis)

The evolution of swimming modes in semi-aquatic and aquatic mammals has several transitional stages as locomotion becomes more energetically efficient. The South American giant river otter (Pteronura brasiliensis) possesses a body morphology that appears to be transitional between semi-aquatic mammals that use paddling propulsion and more aquatic undulatory swimmers. The swimming kinematics of two captive otters was detailed using videography and computer analysis (Peak Motus). Animals swam over a range of velocities, both at the water surface and while submerged. The otters propelled themselves with simultaneous strokes of the hind feet. Paddling strokes were associated with undulatory movements of the dorso-ventrally flattened tail. During the power stroke of the feet, a traveling wave was produced in the tail that moved at a velocity faster than the forward velocity of the otter. A similar wave traveled down the tail during the recovery stroke. Hydrodynamic theory indicates that the laterally expanded tail would generate thrust throughout the stroke cycle. The wave kinematics in the tail of Pteronura suggests a possible evolutionary transitional stage from appendicular to body and tail propulsion.