🐢Plesiosaurs

Four-flippered sea reptiles

Diapsida › Sauropterygia › Plesiosauria

🚫 Not dinosaurs

Plesiosaurs were reptiles that swam in the sea using four big flippers. Some had extra-long necks, and others, called pliosaurs, had giant heads and teeth. They lived at the same time as dinosaurs but were not dinosaurs.

Plesiosaurs are marine reptiles in the group Sauropterygia, which branched off from other reptiles long before dinosaurs appeared, so they are not dinosaurs. They lived from the latest Triassic, about 203 million years ago, until the end-Cretaceous extinction. Instead of swimming with their tails, they "flew" underwater with four wing-like flippers. Long-necked forms such as Plesiosaurus and Elasmosaurus fed on fish and squid-like animals, while short-necked pliosaurs such as Liopleurodon and Kronosaurus were top predators. A Polycotylus fossil with an embryo inside shows that plesiosaurs gave birth to live young rather than laying eggs; the first near-complete Plesiosaurus skeleton was found by Mary Anning in 1823.