Image: Tyrannosaurus rex adults
Copyright 1985 Mark Hallett, "Awakening of Hunger"
Two Tyrannosaurus rex adults are alert and ready to hunt. A pterodactyloid pterosaur Pteranodon ingens overhead. The scene takes place on the margin of a floodplain in the future area of western Montana, during the Hell Creek formational time of the late Cretaceous Period.
updated 6/6/2007 7:47:38 PM ET 2007-06-06T23:47:38

T. rex was no slacker. But the popular image of a nimble predator turning on a dime and chasing down prey with lightning speed is fiction, new computer models show. The terrifying tyrannosaur was actually a slowpoke.

Previous studies have looked at the movements of birds, the direct descendents of dinosaurs, and fossilized footprints to judge how Tyrannosaurus rex would have moved.

To get a better estimate of the giant’s movement, the new study modeled a typical complete T. rex skeleton, which probably weighed between about 13,000 and 17,000 pounds, and estimated its center of mass and the inertia, or resistance to movement, that it would have had when the animal turned or pivoted.

The center of mass is important to consider because two animals with similar weights may move in different ways depending on how their mass is distributed.

For example, an elephant’s four tree trunk-like legs keep its center of mass over its feet, while T. rex would have had to balance its mass differently over its two small legs, bending them to keep from toppling over.

The model results, detailed in the June 21 issue of the Journal of Theoretical Biology, also showed that T. rex would have had considerable inertia preventing it from turning quickly; a 45-degree turn would have taken one or two seconds — far longer than for a human.

These calculations lend further support to previous research indicating that the large tyrannosaurs could run no faster than 25 mph (and certainly not the 45 mph seen in some movies), because its leg muscles weren’t big enough for fast running.

“We now know that a T. rex would have been front heavy, turned slowly and could manage no more than a leisurely jog,” said team leader John Hutchinson of the Royal Veterinary College.

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