The Plesiosaur is not actually a dinosaur, but rather a large swimming reptile. 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.
What did they look like? 
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! They all had long necks with small heads on the end. Their tummies 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 were very successful.
What did they eat? 
They ate fish, squids, mollusks and other small sea creatures. 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? 
They lived from the early Jurassic to the end of the Cretaceous period. That is from about 220 million years to about 65 million years ago. Plesiosaurs, like dinosaurs, lived in the Mesozoic era. Nobody is sure why the plesiosaurs went extinct.
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.
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?