Cryptoclidus ("Hidden Collar Bone") was an 26 foot, eight ton member of a plesiosaur from the Middle to Late Jurassic Period (180-145 MYA) English deposits.
Cryptoclidus lived during the Middle to Late Jurassic period from 180-145 million years ago. It shared the Jurassic oceans with a variety of other sea creatures.
An eight-ton sea reptile, Cryptoclidus were air breathers. On the land, they were cumbersome hulks, but in the water, they were transformed. These animals used all four flippers to chase the blizzards of fish through the water. Flapping like underwater wings, these flippers were used separately to give them enormous maneuverability or together for sudden bursts of speed.
Whenever they dug their jaws in the sand, Cryptoclidus were not searching for food. They were in fact after pebbles and grit. Sieving of the grains, they retained the larger stone in their stomachs for ballast, which weighed them down and contracted the air in their lungs.