What are ancient marine reptiles called?

There were many different marine reptiles during the 'age of the dinosaurs' (the mesozoic era - comprising the Triassic, Jurassic and Cretaceous periods).

These marine reptiles are collectively known as 'sauropterygia' (lizards with flippers) and should not be confused with dinosaurs.

The best known of these is the 'plesiOSaur'.

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