Cryptoclidus

Cryptoclidus (/krɪptɵˈklaɪdəs/ krip-toh-KLY-dəs) was a genus of plesiosaur (a type of marine reptile) from the Middle Jurassic period of England.

Description
Cryptoclidus is estimated to have weighed about 8 tons[clarification needed]. Its head was rather flattened, with eyes facing upward. The skull was broad and light, with jaws lined with about a hundred long, fine teeth, ideal for catching fish and squid. The internal nares were set forward, and the nostrils were relatively small. At up to 8 metres (26 ft) long, Cryptoclidus was a medium-sized plesiosaur.[citation needed]

It had a neck that was up to 2 metres (6.6 ft) long that does not seem to have been very flexible. This probably kept its bulky body away from its small head so as not to alarm potential prey. It had four broad paddle-shaped limbs, with which it either "flew" through the water in wave-like undulating movements, or swam like a porpoise by moving upwards on two flippers and gliding back down again on the other two.

Paleobiology
Due to their seal-like body plan, small plesiosaurs such as Cryptoclidus have been depicted as amphibious animals instead of fully marine reptiles. Despite looking clumsy and cumbersome, in water it would have been relatively graceful, using all four limbs as paddles, to swim and hunt its prey. It may have laid eggs in sand, but this is conjectural.

The fragile build of the head and teeth preclude any grappling with prey, and suggest a diet of small, soft-bodied animals such as squid and shoaling fish. Cryptoclidus may have used its long, intermeshing teeth to strain small prey from the water, or perhaps sift through sediment for buried animals.[2]

The size and shape of the nares and nasal openings have led Brown and Cruickshank (1994) to argue that they were used to sample seawater for smells and chemical traces.