However, neither of these are related to extant sea turtles; the oldest representative of the lineage leading to these was Desmatochelys padillai , from the Early Cretaceous.A lineage of unrelated marine testudines, the pleurodire (side-necked) bothremydids, also survived well into the Cenozoic.Other pleurodires are also thought to have lived at sea, such as Araripemys.Sea turtles' limbs and brains have evolved to adapt to their diets.are reptiles of the order Testudines and of the suborder cryptodira.The seven existing species of sea turtles are: the green, loggerhead, Kemp's ridley, olive ridley, hawksbill, flatback, and leatherback.
The leatherback is the only extant member of the family Dermochelyidae.
The leatherback is the largest species of sea turtle.
Measuring 2–3 meters (6–9 ft) in length, and 1-1.5 m (3–5 ft) in width, weighing up to 700 kilograms (1500 lb).
Instead, it bears a mosaic of bony plates beneath its leathery skin.
In general, sea turtles have a more fusiform body plan than their terrestrial or freshwater counterparts.