In 2022, the giant fossil species Leviathanochelys was described from Spain. The earliest "true" sea turtle that is known from fossils is Nichollsemys from the Early Cretaceous ( Albian) of Canada. Presently thought to be outside the crown group that contains modern sea turtles (Chelonioidea), the exact relationships of protostegids to modern sea turtles are still debated due to their primitive morphology they may be the sister group to the Chelonoidea, or an unrelated turtle lineage that convergently evolved similar adaptations. Desmatochelys was a protostegid, a lineage that would later give rise to some very large species but went extinct at the end of the Cretaceous. The oldest possible representative of the lineage ( Panchelonioidea) leading to modern sea turtles was possibly Desmatochelys padillaifrom the Early Cretaceous. Their closest extant relatives are in fact the snapping turtles (Chelydridae), musk turtles (Kinosternidae), and hickatee ( Dermatemyidae) of the Americas, which alongside the sea turtles constitute the clade Americhelydia. Modern sea turtles are not descended from more than one of the groups of sea-going turtles that have existed in the past they instead constitute a single radiation that became distinct from all other turtles at least 110 million years ago. Other pleurodires are also thought to have lived at sea, such as Araripemys and extinct pelomedusids. A lineage of unrelated marine testudines, the pleurodire (side-necked) bothremydids, also survived well into the Cenozoic. In Africa, the first marine turtle is Angolachelys, from the Turonian of Angola. The leatherback sea turtle is the only extant member of the family Dermochelyidae.įossil evidence of marine turtles goes back to the Late Jurassic (150 million years ago) with genera such as Plesiochelys, from Europe. The superfamily name Chelonioidea and family name Cheloniidae are based on the Ancient Greek word for tortoise: χελώνη ( khelone). All species except the leatherback sea turtle are in the family Cheloniidae. Sea turtles, along with other turtles and tortoises, are part of the order Testudines. 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. The skulls of sea turtles have cheek regions that are enclosed in bone. Other sea turtle species are smaller, being mostly 60–120 cm (2–4 ft) long and proportionally narrower. The leatherback sea turtle is the largest sea turtle, measuring 2–3 m (6–9 ft) in length, 1–1.5 m (3–5 ft) in width, and weighing up to 700 kg (1500 lb). However, the streamlined body plan reduces friction and drag in the water and allows sea turtles to swim more easily and swiftly. 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. In general, sea turtles have a more fusiform body plan than their terrestrial or freshwater counterparts. Descriptionįor each of the seven types of sea turtles, females and males are the same size there is no sexual dimorphism. There is only one dermochelyid species which is the leatherback sea turtle. Sea turtles can be separated into the categories of hard-shelled ( cheloniid) and leathery-shelled ( dermochelyid). The seventh sea turtle species is the flatback, which exists in the waters of Australia, Papua New Guinea and Indonesia. Īll six of the sea turtle species present in US waters (all of those listed above except the flatback) are listed as endangered and/or threatened under the Endangered Species Act. The seven existing species of sea turtles are the flatback, green, hawksbill, leatherback, loggerhead, Kemp's ridley, and olive ridley sea turtles. Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines and of the suborder Cryptodira. A green sea turtle, a species of the sea turtle superfamily
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