By | September 9, 2016

During the Jurassic and Cretaceous periods, when dinosaurs ruled the land, the oceans were ruled by gigantic carnivorous reptiles called plesiosaurs. There were two main types: long-necked plesiosaurs, which had long, snakelike necks and small, dainty heads; and short-necked plesiosaurs (pliosaurs), which had huge heads and enormous, fang-filled jaws.


Key features
■ Plesiosaurs had long necks and small skulls; pliosaurs were short-necked, with enormous skulls
■ Four large flippers
■ Many pointed teeth

Plesiosaurs appeared in the Early Jurassic, 200 million years ago. They died out at the end of the Cretaceous Period, 65 million years ago.

Elasmosaurus (el-LAZZ-moe-SORE-us)


Experts argue over how flexible the long neck of Elasmosaurus was. Some think it was as flexible as a snake’s body and could be coiled up or held right out of the water. Others think it was stiffer but with enough flexibility to bend down and reach far to each side.

When: 99–65 million years ago (Late Cretaceous)

Fossil location: USA

Habitat: Oceans

Length: 45 ft (14 m)

Diet: Fish, squid, shellfish

Elasmosaurus’s neck was as long as the rest of its body. After its discovery in 1868, the first scientists to study this animal thought the long neck was its tail and so put the head at the wrong end. This long neck came in handy—as Elasmosaurus swam slowly over the seabed, it would reach down to pick prey off the bottom.

Plesiosaurus (PLEE-see-oh-SORE-us)


When: 200 million years ago (Early Jurassic)

Fossil location: British Isles, Germany

Habitat: Oceans

Length: 10–15 ft (3–5 m)

Diet: Fish, squidlike mollusks

Plesiosaurus was a long-necked aquatic reptile with a wide, turtlelike body. Like a turtle, it pushed itself through the water using its flippers, as the tail was too short to be of much use. It hunted by swimming among shoals of fish, swinging its long neck from side to side to snatch its prey. Plesiosaurus had U-shaped jaws, which it could open wide, trapping prey with its conical teeth.

Liopleurodon (LIE-oh-PLOOR-oh-don)


Each of the bones in Liopleurodon’s spine was the size of a dinner plate.

When: 165–150 million years ago (Mid to Late Jurassic)

Fossil location: British Isles, France, Russia, Germany

Habitat: Oceans

Length: 16–23 ft (5–7 m)

Diet: Large squid, ichthyosaurs

One of the most powerful carnivores of all time, Liopleurodon had massive jaws and probably a stronger bite than Tyrannosaurus. It could easily have held a medium-sized car in its mouth and bitten it in half. Scientists believe it had a strong sense of smell, which helped it to hunt in deeper waters where prey was difficult to spot.

Kronosaurus (crow-no-SORE-us)



When: 65 million years ago (Late Cretaceous)

Fossil location: Australia, Colombia

Habitat: Oceans

Length: 33 ft (10 m)

Diet: Marine reptiles, fish, mollusks

Kronosaurus was one of the largest sea reptiles. Even its head, at almost 10 ft (3 m) long, was bigger than a man. This monster could open its jaws wide like a crocodile and grasp prey with teeth as big as bananas. Fossilized stomach remains show that it ate other marine reptiles, including other plesiosaurs. Like all plesiosaurs, it had to rise to the surface to breathe air.


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