Transitions from Drag-based to Lift-based Propulsion in Mammalian Swimming

Abstract

Synopsis. The evolution of fully aquatic mammals from quadrupedal, terrestrial mammals was associated with changes in morphology and swimming mode. Drag is minimized by streamlining body shape and appendages. Improvement in speed, thrust production and efficiency is accomplished by a change of swimming mode. Terrestrial and semiaquatic mammals employ drag-based propulsion with paddling appendages, whereas fully aquatic mammals use lift-based propulsion with oscillating hydrofoils. Aerobic efficiencies are low for drag-based swimming, but reach a maximum of 30% for lift-based propulsion. Propulsive efficiency is over 80% for lift-based swimming while only 33% for paddling. In addition to swimming mode, the transition to high performance propul? sion was associated with a shift from surface to submerged swimming providing a reduction in transport costs. The evolution of aquatic mam? mals from terrestrial ancestors required increased swimming performance with minimal compromise to terrestrial movement. Examination of modern analogs to transitional swimming stages suggests that only slight modification to the neuromotor pattern used for terrestrial locomotion is re? quired to allow for a change to lift-based propulsion.