On a cold winter's day in 1811, a boy and a girl were walking beside the sea in Lyme Regis, south-west England. They were alone, and they walked slowly, looking at the stones under their feet. The sea on their right was still and grey. On their left, near the land, there were a lot of large, broken rocks.
The children were looking for something.
The girl, Mary Aiming, was about twelve years old. Every few minutes, she picked up a stone, looked at it carefully, and put it in her bag. Then the boy, her older brother Joseph, began to climb over the broken rocks. It was dangerous; both children knew that. There had been a storm the night before, and some rocks had fallen into the sea. Another big rock could fall at any time.
But the morning after a storm was also the best time to look for fossils - the bones of animals or parts of plants that had become hard and changed into rock.
After a few minutes, Joseph called out to his sister, 'Mary! Quick! Come and look at this!'
When Mary climbed up to him, he showed her a line of teeth, half a metre long, in the broken rock. And behind the teeth, there were some bones, like the head of a strange animal. 'It's a crocodile, isn't it?' Joseph said. 'We've found a crocodile in the rocks!'
Mary looked carefully at the head of the strange animal that Joseph had found.
'What's that round thing?' she asked. 'Look, there, behind the teeth.'
As she cleaned away some sand from the head, a bony circle stared back at them.
'That must be its eye,' Mary said. 'Look - it's almost as big as my head!'
Her brother laughed. 'And its mouth is as big as your body. Be careful, Mary. Look at those teeth! It's going to eat you!'
'Don't be silly,' Mary said. 'It's dead. It died hundreds of years ago. Come on, we've got to find the rest of its body too.'
Some men helped the children to get the bones of the dead animal out of the rock. It was about four metres long, with flat, bony hands and a long tail. It had huge eyes and a long mouth full of sharp teeth. At first, people thought it was a crocodile, but it was not. It was an animal quite different from anything alive in the world today. In 1818, two scientists called Henry de la Beche and William Conybeare gave it the name Ichthyosaurus.