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,
Wallowa Mountains addition there are many older terranes between the batholith and basalt flows. The Wallowa Batholith is formed of granite from a magma upwelling in Late Jurassic and Early Cretaceous time (between 160 million and 120 million years ago). The placement of this rock caused uplift of the surface, which at the time was tropical sea. This is evident from the slate, quartzite, and marble present in the mountains, which come from metamorphism of the sedimentary deposits of oceans during the Triassic. At the center of the Batholith are granodioritic rocks, while the outer limits of the range are tonalitic. The