Thalattosauria is an extinct order of prehistoric marine reptiles that lived in the Middle to Late Triassic. Thalattosaurs were diverse in size and shape, and are divided into two superfamilies: Askeptosauroidea and Thalattosauroidea. Askeptosauroids were endemic to the Tethys Ocean, their fossils have been found in Europe and China, and they were likely semiaquatic fish eaters with straight snouts and decent terrestrial abilities. Thalattosauroids were more specialized for aquatic life and most had unusual downturned snouts and crushing dentition. Thalattosauroids lived along the coasts of both Panthalassa and the Tethys Ocean, and were most diverse in China and western North America. The largest species of thalattosaurs grew to over 4 meters (13 feet) in length, including a long, flattened tail utilized in underwater propulsion. Although thalattosaurs bore a superficial resemblance to lizards, their exact relationships are unresolved. They are widely accepted as diapsids, but experts have variously placed them on the reptile family tree among Lepidosauromorpha, Archosauromorpha, ichthyosaurs, and/or other marine reptiles.
Many 20th-century paleontologists considered thalattosaurs to be an independent offshoot of formerly terrestrial reptiles closely related to squamates (such as lizards) or rhynchocephalians (such as the tuatara, pictured)
Thalattosaurs have been proposed to be related to various reptile groups including archosauromorphs, sauropterygians, and ichthyosaurs (such as Temnodontosaurus, pictured)
Image: Anshunsaurus huangguoshuensis NTM
Image: Askeptosaurus italicus
Marine reptiles are reptiles which have become secondarily adapted for an aquatic or semiaquatic life in a marine environment. Only about 100 of the 12,000 extant reptile species and subspecies are classed as marine reptiles, including marine iguanas, sea snakes, sea turtles, and saltwater crocodiles.
Reptiles that live in the sea: • Saltwater crocodile (top left) • Sea turtle (top right) • Marine iguana (bottom left) • Sea snake (bottom right)
Hawksbill sea turtle (Eretmochelys imbricata)
Fossil of Ophthalmosaurus icenius, a species of ichthyosaur