The animal ran across a Jurassic Oxfordshire

The evidence comes from a quarry in Oxfordshire, UK, where Julia Day and colleagues at Cambridge University have been studying the feet impressions left by the bi-pedal hunters and long-necked plant-eaters, the sauropods.

In a report in the journal Nature, the scientists describe how one set of theropod tracks clearly reveals the creature breaking from a walk into a run. When walking, the stride is about 2.7 metres in length, which increases to 5.5 metres at its fastest.

The tracks also begin to look quite different. "During the walking phase, the dinosaurs have their feet splayed out widely, with the toes pointing inwards, pigeon-toed fashion," says Dr Day.

"That's quite unusual for a theropod dinosaur. All the trackway evidence until now has shown that their feet are tucked underneath."

By contrast, when the creatures picked up speed, the feet were then tucked underneath their bodies, like mammals today, she said.

Under landfill

Scientists had always thought that the theropods could run, but the Cambridge team believe they're the first with proof from tracks of medium-sized or large theropods running. They have calculated that one particular animal walked at about 7 km per hour (a human walks at about 6 km/h) and ran as fast as 30 km/h.

It is thought the dinosaur was a Megalosaurus. From the tracks, the researchers estimate it has a hip height of about 2 m and measures about 7 m long.

"We're not entirely sure," said Dr Day. "But we have one line of evidence that in nearby quarries of a similar age there are signs of a large theropod called Megalosaurus and we think that's a very good candidate for this dinosaur too."

With sauropod tracks on the same spot, her guess is that the huge racing theropods were chasing their prey - a herd of sauropods.

The site of the find - Ardley Quarry in Oxfordshire - contains one of the most extensive dinosaur-trackway sites in the world, with some extending for up to 180 m. Some of those that have been studied are gradually being covered over, as the area has been designated as a rubbish dump.

However, the scientists hope more tracks will be revealed there as new layers are continually exposed.