Theropods walked on two legs

[Jack Kolb <kolb@ucla.edu>]

http://news.bbc.co.uk/hi/english/sci/tech/newsid_1791000/1791709.stm

 Wednesday, 30 January, 2002, 19:21 GMT
Theropods walked on two legs
By BBC science correspondent Christine McGourty

Fossilised dinosaur tracks that are 163 million years old have revealed how 
large meat-eating theropod dinosaurs could break into a run when chasing 
their prey.

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.