Plesiosaur Dilatational (Compressional) Propagation (non-flipper) for Propulsion

Plesiosaurs use flipper and non-flipper propulsion; which is why plesiosaurs (>43 vertebrae) appear as "gliding" either surfaced or submerged. This would of course apply also to Elasmosaurs (>70 vertebrae). Reptiles (snakes) use this method of longitudinal propulsion.