Sea turtle

Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines and of the suborder Cryptodira. The seven existing species of sea turtles are the green sea turtle, loggerhead sea turtle, Kemp's ridley sea turtle, olive ridley sea turtle, hawksbill sea turtle, flatback sea turtle, and leatherback sea turtle..mw-parser-output .toclimit-2 .toclevel-1 ul,.mw-parser-output .toclimit-3 .toclevel-2 ul,.mw-parser-output .toclimit-4 .toclevel-3 ul,.mw-parser-output .toclimit-5 .toclevel-4 ul,.mw-parser-output .toclimit-6 .toclevel-5 ul,.mw-parser-output .toclimit-7 .toclevel-6 ul{display:none} The majority of a sea turtle's body is protected by its shell, which is divided in two: the carapace (dorsal/top) and the plastron (ventral/underside). The shell is made up of smaller plates called scutes. The leatherback sea turtle is the only sea turtle that instead of a hard shell has a leathery skin covering a mosaic of bony plates. Importantly, for each of the seven types of sea turtles, females and males are the same size—no sexual dimorphism. In general, sea turtles have a more fusiform body plan than their terrestrial or freshwater counterparts. This tapering at both ends reduces volume and means sea turtles can’t, as can other turtles and tortoises, retract their head and limbs into their shells for protection. But the streamlined body plan reduces friction and drag in the water and allows sea turtles to swim more easily and swiftly. The leatherback sea turtle is the largest 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). Other sea turtle species are smaller, being mostly 60–120 cm (2–4 ft) long and proportionally narrower. Sea turtles, along with other turtles and tortoises, are part of the order Testudines. All species except the leatherback sea turtle are in the family Cheloniidae. The leatherback sea turtle is the only extant member of the family Dermochelyidae. The origin of sea turtles goes back to the Late Jurassic (150 million years ago) with genera such as Plesiochelys, from Europe. In Africa, the first sea turtle is Angolachelys, from the Turonian of Angola. 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 constitute a single radiation that became distinct from all other turtles at least 110 million years ago.