Sea turtles are turtles that inhabit all of the world's oceans except the Arctic. Sea turtles, along with other turtles and tortoises, are part of the order Testudines. The leatherback belongs to the family Dermochelyidae and is its only member. Sea turtles constitute a single radiation that became distinct from all other turtles at least 110 million years ago.
Sea turtles are large, air-breathing reptiles that inhabit tropical and subtropical seas throughout the world. Their shells consist of an upper part and a lower section. Hard scales cover all but the leatherback, and the number and arrangement of these scutes can be used to determine the species.
Only females come ashore to nest; males rarely return to land after crawling into the sea as hatchlings. Most females return to nest on the beach where they were born. Nesting seasons occur at different times around the world. In the U.S., nesting occurs from April through October. Most females nest at least twice during each mating season; some may nest up to ten times in a season. A female will not nest in consecutive years, typically skipping one or two years before returning.