Plesiosaurs and Pliosaurs
Plesiosaurs were highly skilled swimmers in the seas and they first appeared on Earth 170 million years ago. Early on in their evolution they were divided into two groups by experts, one is known as the plesiosaurs and other one is called pliosaurs. Plesiosaurs were more like fat dolphins with long necks and had heads the shape of a snake. Pliosaurs had plump bodies, short necks and crocodile-like heads.
The largest know plesiosaur was the Elasmosaurus which measured 15 meters from its head to tail. That is an extremely long sea reptile. Half of its body length was made up by its neck, which had over 70 tiny bones in it. The advantage of this long neck is, the Elasmosaurus could catch a passing fish in an instant. It may even have stretched its long neck out of the water to grab at an unsuspecting pterosaur (flying reptile) gliding just above the sea. Another long-necked plesiosaur was the Cryptoclidus. This marine creature measured only 3 meters long, but it was as agile as an otter and just as skilled and dangerous for hunting.
Pliosaurs had shorter necks than the plesiosaurs. They looked like whales with massive jaws and armed with lethal teeth. They fed on big fish and probably did not hesitate to go after tinier sea reptiles that came within their path. Pliosaurs were ideally suited to living in the water all the time. Some pliosaurs could dive down to depths of up to 300 meters in search of their prey. In Greek legend there was a mythical god named Kronos who ate his own children. When the fossil of a short-necked pliosaur with jaws 3 meters long and teeth the size of sharp carving knives was discovered, experts named it Kronosaurus after the bloodthirsty Greek god, Kronos.
Plesiosaurs and pliosaurs shared the waters with several other marine reptiles. One in particular, the Geosaurus, was an early ancestor of crocodiles of today. Geosaurus used its broad paddles to steer, compared to the pliosaurs which used their paddles to move along forward. Geosaurus could bend its body from side to side, just like an eel, and it weaved through the water on the look out for fish nearby.
Fossil of a Kronosaurus
Deborah Brooks Langford from Brownsville,TX on August 21, 2012:
wow this hub is awesome and interesting.. I just went to the zoo in Memphis couple of months ago. They had fossils of dinosaurs.. that was the best part of the Zoo besides the black Panthas which are my favorite animals..
I will share this
Michelle Liew from Singapore on August 21, 2012:
Welcome to hubpages!! It's nice to see a dinosaur fan. I don't think I know so much about dinosaurs,but I do know that they're awesome creatures . Wonderful facts about them which I learned so much about!! Will be coming by!