![]() The term "plesiosaur" is properly used to refer to the Plesiosauria as a whole, but informally it is sometimes meant to indicate only the long-necked forms, the old Plesiosauroidea.įirst published plesiosaur skeleton, 1719 "Plesiosauroidea" and "Pliosauroidea" today have a more limited meaning. Therefore, the purely descriptive terms "plesiosauromorph" and "pliosauromorph" have been introduced, which do not imply a direct relationship. Modern research, however, indicates that several "long-necked" groups might have had some short-necked members or vice versa. The two types are related to the traditional strict division of the Plesiosauria into two suborders, the long-necked Plesiosauroidea and the short-neck Pliosauroidea. Other species, some of them reaching a length of up to seventeen metres, had the "pliosauromorph" build with a short neck and a large head these were apex predators, fast hunters of large prey. ![]() Some species, with the "plesiosauromorph" build, had (sometimes extremely) long necks and small heads these were relatively slow and caught small sea animals. Plesiosaurs showed two main morphological types. Plesiosaurs breathed air, and bore live young there are indications that they were warm-blooded. The flippers made a flying movement through the water. ![]() Their limbs had evolved into four long flippers, which were powered by strong muscles attached to wide bony plates formed by the shoulder girdle and the pelvis. Plesiosaurs had a broad flat body and a short tail. In the early twenty-first century, the number of discoveries has increased, leading to an improved understanding of their anatomy, relationships and way of life. Since then, more than a hundred valid species have been described. The first plesiosaurian genus, the eponymous Plesiosaurus, was named in 1821. In the beginning of the nineteenth century, scientists realised how distinctive their build was and they were named as a separate order in 1835. Plesiosaurs were among the first fossil reptiles discovered. They had a worldwide oceanic distribution, and some species at least partly inhabited freshwater environments. They became especially common during the Jurassic Period, thriving until their disappearance due to the Cretaceous–Paleogene extinction event at the end of the Cretaceous Period, about 66 million years ago. Plesiosaurs first appeared in the latest Triassic Period, possibly in the Rhaetian stage, about 203 million years ago. The Plesiosauria ( / ˌ p l iː s i ə ˈ s ɔːr i ə, - z i-/ Greek: πλησίος, plesios, meaning "near to" and sauros, meaning "lizard") or Plesiosaurs are an order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia.
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