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DON鈥橳 believe everything you see in the movies. As well as putting
Tyrannosaurus rex alongside dinosaurs that actually lived tens of millions
of years earlier, Jurassic Park portrayed the fearsome beast as an
adept sprinter, capable of catching a speeding car.

But this piece of artistic licence literally went a step too far: T.
rex was actually a lumbering giant incapable of even breaking into a gentle
jog, say two specialists in biomechanics.

John Hutchinson and Mariano Garcia of the University of California at
Berkeley calculated that a 6-tonne T. rex couldn鈥檛 have carried enough
leg muscle to break into a run. Instead it could only walk at a respectable 5
metres per second, just half the top speed clocked for an elephant or a top
human sprinter.

Palaeontologists have been arguing about the top speed of giant predatory
dinosaurs for years. In a bid to resolve the dispute, Hutchinson, now at
Stanford University, developed a model for calculating the muscle mass an animal
would need to run on two-legs, based on its size, weight and posture. The
requirements increase with body mass. A running chicken in their model would
need at least 4.7 per cent of its body mass in muscle in each leg; an actual
chicken has 8.8 per cent. In contrast, a full-size T. rex would have
needed muscle weighing 43 per cent of its body mass in each leg to get up a bit
of speed鈥攁 practical impossibility. Hutchinson is confident the model 鈥渋s
going to hold for large dinosaurs in general鈥�. That means T. rex would still
have been able to catch its ambling herbivorous prey.

The model seems reasonable, says Jim Farlow of Indiana University-Purdue
University, Fort Wayne. The tracks of a large dinosaur recently discovered in
Britain indicate the animals were moving about 8 metres per second, Farlow
estimates, but that includes a large margin of error. He has also suggested that
running too fast would have been a bad idea for giants such as T. rex
because a fall could have been lethal.