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,
Lake Parime the Takutu Basin or the Takutu Formation, dates back to the late Paleozoic, roughly 250 million years ago, and the basin connected with the Atlantic via the Takutu Graben. The geologic history of the Takutu Graben is characterized by one phase of volcanic activity and three depositional phases of sedimentary rocks. Rifting (due to divergent tectonic plate movements) occurred in "a lake or delta environment" in the Late Triassic to Early Jurassic periods, between 200 million and one hundred and fifty million years ago. Starting around 66,000 years ago, sea level rise and more humid conditions created flooded zones north