Wikijunior:Dinosaurs/Plesiosaur

A picture of a Rhomaleosaurus with a long neck.

The plesiosaur, more named correctly as Elasmosaurus, is not actually a dinosaur, but rather a large swimming reptile. The word plesiosaur is Greek for "nearer to the reptiles". This name given to this creature because it resembles something that is part reptile and part fish. The whole group of these animals are called plesiosaurs, pliosaurs and elasmosaurs.

What did they look like?

Dinosaurs

Tyrannosaurus Rex Stegosaurus Allosaurus Apatosaurus Pterosaurs Triceratops Plesiosaur Ichthyosaur Pachycephalosaurus Velociraptor Herrerasaurus Ankylosaurus Iguanodon Brontosaurus

An early image of the Plesiosaurus, surprisingly accurate with only one problem.

There were different types of plesiosaurs which were different from each other in size and in shape. The shortest were 2.5 metres long and the longest were 14 metres long! That is about as long as 8 adults lying in one long line! Some had long necks with small heads on the end, others had short necks with immense jaws (pliosaurs). Their stomachs were oval-shaped with two front flippers and two back flippers. They had long tails, though much shorter than their necks.

Scientists first thought that they swam close to the surface of the water (as the picture on the left shows). This way they could stick their head above the water and look down on fish. But because their eyes are placed facing slightly upwards, this is probably not true. They probably swam completely underwater and used their long necks to dart their heads towards fish. Plesiosaurs and their relatives were highly successful throughout the Mesozoic.

What did they eat?

Their tooth structure and gut remains showed they ate mostly invertebrates, so things like cephalapods. They ate fish, squids, mollusks and other small sea creatures. Very recently, scientists have found evidence that the plesiosaurs may have also been "bottom-feeders". That is, they would feed from the bottom of the sea - on things like clams and snails.

When did they live?

Rhomaleosaurus lived from the early Jurassic, while Elasmosaurus lived in the late Cretaceous. That is from about 220 million years to about 66 million years ago. Plesiosaurs, like dinosaurs, lived in the Mesozoic. Nobody is sure why the plesiosaurs went extinct on Earth.

Where did they live?

Some people think that they could climb out of the water and crawl around on land, like seals. But other scientists disagree with this. Either way they would have spent a lot of their time under water. And because they were air-breathing animals, they would have to come up to the water surface for air every now and then.

Their fossils were found in England, Germany, Korea, Australia, New Zealand and USA. They also lived in Manitoba, Canada,and Mexico

How were they discovered?

The first plesiosaur was discovered in 1821 by Mary Anning, in England. Mostly found in the Benthic zone, they can also be found in the intertidal zones as well.

Modern mysteries around the Plesiosaurs

The most famous mysteries around these creatures is the Loch Ness Monster. There are a lot of stories of some large creature in the lake called Loch Ness in Scotland. Most descriptions of the monster are close to what the plesiosaurs must have looked like. Some of the sightings have been proven to be a hoax and at present there is no scientific proof of the existence of the animal but many people believe in it. The study and search for animals which fall outside of contemporary zoological catalogues has the name of Cryptozoology.

In 1977, some Japanese fishermen off the coast of New Zealand found a very rotten carcass of some large creature with flippers. It was so rotten that it was very hard to tell anything from it, but some people believed that it was a plesiosaur. Scientists however ascertained it was a basking shark, fallen to bits because it was so rotten.

What do we need to learn?

• How flexible were their necks? Scientists don't agree on this.
• Is there any truth to the stories around them?