Plesiosauria Plesiosauria The Plesiosauria (; Greek: πλησίος, "plesios", meaning "near to" and "sauros", meaning "lizard") or plesiosaurs are an order or clade of Mesozoic marine reptiles (marine Sauropsida), belonging to the Sauropterygia. Plesiosaurs first appeared in the latest Triassic Period, possibly in the Rhaetian stage, about 203 million years ago. 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. They had a worldwide oceanic distribution. Plesiosaurs were among the first fossil reptiles discovered. In the beginning of the nineteenth century,
Eldon George as a sparrow or robin. In 1986, a scientific team that included Paul Olsen, discovered hundreds of thousands of fossils at Wasson Bluff, one of the biggest troves ever found. Fossil discoveries on the Fundy shoreline are especially significant because they date from 200 million years ago, the boundary between the Triassic and Jurassic geological periods, when about half of the Earth's living creatures suddenly became extinct giving rise to dinosaurs and the mammals that eventually succeeded them. Many of the fossils that date from that time remain hidden, buried under North American forests, farmland or cities. But, the Fundy