Early Jurassic
Plesiosauridae
Long-necked marine reptiles — not dinosaurs, but a separate lineage that returned to the sea while dinosaurs still ruled the land. Plesiosaurus, unearthed by Mary Anning in 1823, was one of the fossils that first convinced the world extinct monsters had truly existed.
Not a dinosaur — marine reptileExtremely long neckFour large paddle-like flippersFirst described by Mary Anning
Plesiosauridae