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,
Carabobo Field attributed to the formation of the field is when North America separated from Gondwanaland in the Late Triassic/Early Jurassic (~200 million years ago). The rifting in this period is represented by Late Jurassic basalts deposited in the Espino graben. This event led to the northern passive margin of South America. During the Cretaceous Period (~150 million years ago), the passive margin began to subside from organic rich sediments being deposited. This deposition includes the Querecual and San Antonio formations that would become source rocks for the Orinoco Oil Belt. The next tectonic event is referred to as a progressive collision