Sea turtles

Sea turtles and the pig-nosed turtle are the most specialized for aquatic locomotion. Their front limbs have evolved into flippers while the shorter

hind limbs are shaped more like rudders. The front limbs provide most of the thrust for swimming, while the hind limbs serve as stabilizers.[18][27] Sea turtles such as Chelonia mydas rotate the front limb flippers like a bird’s wings so as generate a propulsive

force on both the upstroke and on the downstroke. This is in contrast to similar-sized freshwater turtles (measurements having been made on young animals in each case) such as Mauremys caspica, which use the front limbs like the oars of a rowing boat, creating substantial

negative thrust on the recovery stroke in each cycle. In addition, the streamlining of the marine turtles reduces drag. As a result, marine turtles produce a propulsive force twice as large, and swim six times as fast, as freshwater turtles. The swimming efficiency of young marine turtles is similar to that of fast-swimming fish of open water, like mackerel.[26]

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