Dinosaur footprints discovered in Oxfordshire have revealed the Jurassic giant that left them could reach the speed of top Olympic sprinters.

The footprints, some the size of a small child, lay hidden for 168 million years until they were unearthed at a quarry in Ardley, near Bicester.

The discovery of about 30 sets of dinosaur tracks, each measuring up to 200m long, has led scientists to conclude the creatures which left them could run at speeds of nearly 20mph.

The enormous three-toed footprints, some complete with impressions of claws, were preserved in fossilised limestone at the quarry site and discovered in March, 1999.

Experts believe some of the imprints were made by the carnivorous Megalosaurus, which grew up to eight metres long, walked on its two back legs and weighed an estimated ten tonnes.

Changes in the tracks show how the meat-eater swaggered along with its feet wide apart, but ran by placing one foot in front of the other, reaching speeds rivalling those achieved by some of the world's fastest men.

Philip Powell, assistant curator of geological collections at Oxford University's Museum of Natural History, said: "The research has opened up all kinds of questions about whether other dinosaurs that walked on two feet could run and how long they could keep it up for, as the trackway does not show the dinosaur slowing down. We also do not know what the maximum speed it could have reached would have been."

Mr Powell said the tracks found at the Ardley quarry are the longest to have been discovered in Britain.

He said: "The chances of them being preserved is fairly small because you do not often get large expanses of a single bedding plain of rock where footprints are likely to be preserved in wet mud, which is then dried and subsequently buried under a temporary flood of mud."

Round pothole-like tracks were also discovered at the site, which are thought to have been made by a four-footed brontosaur-type dinosaur, with a big body, long thin neck and long tail.

Mr Powell said the tracks provided no evidence of any interaction between the two types of dinosaur.

The tracks will eventually be lost again, as the quarry is now being used as a landfill site.

A reconstruction of the Megalosaurus's trail can be viewed stretching 60m across the natural history museum's lawn in Parks Road, Oxford.

Concrete casts of the footprints are also on display in the museum.