Sea turtles (superfamily Chelonioidea), sometimes called marine turtles,[3] are reptiles of the order Testudines and of the suborder Cryptodira. The seven existing species of sea turtles are the flatback, green, hawksbill, leatherback, loggerhead, Kemp's ridley, and olive ridley.[4][5] Six of the seven sea turtle species, all but the flatback, are present in U.S. waters, and are listed as endangered and/or threatened under the Endangered Species Act.[6] All but the flatback turtle are listed as threatened with extinction globally on the IUCN Red List of Threatened Species. The flatback turtle is found only in the waters of Australia, Papua New Guinea, and Indonesia.[7][6] Sea turtles Temporal range: Early Cretaceous-Holocene,[1] 110β0 Ma PreκκOSDCPTJKPgN A green sea turtle, a species of the sea turtle superfamily Scientific classificationEdit this classification Domain: Eukaryota Kingdom: Animalia Phylum: Chordata Class: Reptilia Order: Testudines Suborder: Cryptodira Clade: Americhelydia Clade: Panchelonioidea Superfamily: Chelonioidea Bauer, 1893[2] Families Dermochelyidae Cheloniidae β Ctenochelyidae Synonyms[2] Chelonii - Oppel, 1811 Chlonopteria - Rafinesque, 1814 Cheloniae - Schmid, 1819 Edigitata - Haworth, 1825 Oiacopodae - Wagler, 1828 Pterodactyli - Mayer, 1849 Sea turtles can be categorized as hard-shelled (cheloniid) or leathery-shelled (dermochelyid).[8] The only dermochelyid species of sea turtle is the leatherback.[8] Description For each of the seven species of sea turtles, females and males are the same size. As adults, it is possible to tell male turtles from female turtles by their long tails with a cloacal opening near the tip. Adult female sea turtles have shorter tails, with a cloacal opening near the base. Hatchling and sub-adult turtles do not exhibit sexual dimorphism; it is not possible to determine their sex by looking at them.[9] 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 that sea turtles cannot retract their head and limbs into their shells for protection, unlike many other turtles and tortoises.[10] However, 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, reaching 1.4 to more than 1.8 m (4.6 to 5.9 ft) in length and weighing between 300 and 640 kg (661 to 1,411 lbs).[11] Other sea turtle species are smaller, ranging from as little as 60 cm (2 ft) long in the case of the Kemp's ridley, which is the smallest sea turtle species, to 120 cm (3.9 ft) long in the case of the green turtle, the second largest.[5][12] The skulls of sea turtles have cheek regions that are enclosed in bone.[13][14] Although this condition appears to resemble that found in the earliest known fossil reptiles (anapsids), it is possible it is a more recently evolved trait in sea turtles, placing them outside the anapsids.[15][13]
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