Constraining Hydrodynamics of Plesiosaur Locomotion

What is the role of the near-identical tandem pairs of flippers found in plesiosaurs? Here, we attempt to elucidate the function of this unique adaptation through a combination of dimensionless scaling, and by comparison with an experimental abstraction composed of a tandem pair of NACA 0012 airfoils. In the airfoil study, it is found that maximum thrust is achieved in rear-biased propulsion (when the hind-foil had a greater amplitude than the forward foil), suggesting that the flippers are more tightly-coupled than previosly thought. Forward-biased propulsion had significantly reduced thrust, often less than that of a single foil of equivalent amplitude. Moreover, the reduced flapping amplitude of the front airfoil corresponds to fossil measurements suggesting that plesiosaurs with low aspect-ratio flippers, which are thought to be more agile species and therefore required greater thrust production, had more developed pelvic girdles (that is, they were suited to a rear-biased gait).