Plesiosauria

Plesiosauria is an extinct group of marine reptiles that lived from the Triassic to the end of the Cretaceous. Its members propelled themselves with four paddle-like limbs and were not dinosaurs.

Sauropterygia: An extinct group of aquatic reptiles that included plesiosaurs and their close relatives. Plesiosauria belongs within this broader lineage of marine reptiles.
Underwater flight: A mode of aquatic propulsion in which paired fins or flippers generate lift and thrust through oscillating strokes. Plesiosaurs are often understood as underwater fliers using their four flippers.
Triassic: The geologic period from about 252 to 201 million years ago, preceding the Jurassic. Plesiosaur origins lie near the end of this period.
Plesiosaurus: A genus of long-necked plesiosaur from the Early Jurassic of Europe. Its fossils helped establish the group’s characteristic long-necked body plan.
Ichthyosauria: An extinct group of marine reptiles with streamlined bodies and fishlike or dolphin-like outlines. Ichthyosaurs swam with tail flukes, unlike plesiosaurs’ four-flipper propulsion.
Plesiosauromorpha: A major plesiosaur lineage generally characterized by long necks and relatively small heads. Its long-necked members show one of the group’s most recognizable body plans.
Hydrodynamics: The study of how fluids move and exert forces on bodies. Hydrodynamic principles help explain how plesiosaur flippers moved through water.
Jurassic: The geologic period from about 201 to 145 million years ago, marked by diverse marine reptiles. Plesiosaurs diversified widely in Jurassic seas.
Liopleurodon: A genus of large-headed pliosaur from the Middle to Late Jurassic. It exemplifies the short-necked, powerful-jawed end of plesiosaur diversity.
Mosasauridae: An extinct family of large marine lizards that flourished during the Cretaceous. Mosasaurs were lizards, not plesiosaurs, and propelled themselves mainly with their tails.

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