Henodus

Henodus is an excellent example of how nature tends to produce similar shapes among creatures with similar lifestyles. This marine reptile of the Triassic period looked uncannily like a prehistoric turtle, with a broad, flat shell covering most of its body, short, clawed feet poking out the front, and a small, blunt, turtle-like head; it probably lived like a modern turtle, too, plucking shellfish out of the water with its knobby beak. However, Henodus was very unlike modern turtles in terms of its anatomy and physiology; it's actually classified as a placodont, a family of prehistoric reptiles typified by Placodus.