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,
Geography of Switzerland term covers entire geological movements contributing to the of the Alps’ formation. A crystalline basement formed at the beginning of the Paleozoic era, between 540 and 360 millions years ago. Later, between 205 and 96 million years ago, the alpine ocean or Tethys Ocean formed between Eurasia and Africa. The ocean reached its maximum width at the end of Jurassic period, 135 million years ago. The collision between the Eurasian and African plates made it progressively disappear. This plate collision (still in progress) began 100 million years ago. The Alps resulted from this geological movement, the two plates creating folding