Sea turtles (Chelonioidea) are turtles found in all the world's oceans except the Arctic Ocean, and some species travel between oceans. The term is US English. In British English they are simply called "turtles"; fresh-water chelonians are called "terrapins" and land chelonians are called tortoises.
The earliest known turtles are from the Middle Jurassic. So, turtles are one of the oldest surviving reptile groups: they are more ancient than snakes or crocodiless. 
There are seven species of sea turtle: Kemp's ridley sea turtle, the olive ridley, the flatback, the green, the loggerhead, the hawksbill and the leatherback.
All but the leatherback are in the family Chelonioidea. The leatherback belongs to the family Dermochelyidae and is its only member. The leatherback sea turtle is the largest, measuring six or seven feet (2 m) in length at maturity, and three to five feet (1 to 1.5 m) in width, weighing up to 2000 pounds (about 900 kg). Most other species are smaller, being two to four feet in length (0.5 to 1 m) and proportionally less wide. The flatback turtle is found only on the northern coast of Australia.
- ↑ Joyce, Walter G. (2017). "A review of the fossil record of basal Mesozoic turtles". Bulletin of the Peabody Museum of Natural History. 58 (1): 65–113. doi:10.3374/014.058.0105. S2CID 54982901. Archived from the original (PDF) on May 31, 2019. Retrieved June 2, 2019.
- Spotila, James R. 2004. Sea turtles: a complete guide to their biology, behavior, and conservation. Baltimore: Johns Hopkins University Press. ISBN 0-8018-8007-6
- Davidson, Osha Gray. 2001. Fire in the turtle house: the green sea turtle and the fate of the ocean. United States: United States of Public Affairs. ISBN 1-5864-8199-1
- Witherington, Blair E. 2006. Sea turtles: an extraordinary natural history of some uncommon turtles.
- SWOT – The state of the world's sea turtles – The most up-to-date information on global sea turtle populations
- Oceana scientists are tracking turtles in the Mediterranean and the Atlantic to find out more about their habits in the deep sea
- Conserving Turtles on a Global Scale
- Underwater video Archived 2008-05-14 at the Wayback Machine of turtles in the Red Sea, Egypt
- Preserving Turtles Archived 2018-12-25 at the Wayback Machine