Thalattosauria is an extinct order of marine reptiles that lived during the Triassic Period. Thalattosaurs were diverse in size and shape, and are divided into two superfamilies: Askeptosauroidea and
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)