Was T. Rex Really a Slowpoke?

Jurassic Park sent millions of moviegoers running for cover — especially with the scene in which a Tyrannosaurus rex almost catches a jeep. It was good movie-making — it just wasn't quite accurate.

A 65-million-year-old dinosaur chasing a modern-day car? That wasn't the problem. It's just that the car would have gotten away much more easily.

John Hutchinson saw the film, and says he greatly enjoyed it. But he happens to be an evolutionary biomechanist — a scientist who studies how ancient animals moved.

"How a 13,000-pound, two-legged animal would be able to run 45 miles an hour just seemed really strange to me," says Hutchinson, now a researcher at Stanford University.

Computerized Carnivore

Back at the lab, Hutchinson and his colleague, Mariano Garcia, created a computer model of T. rex. In this week's edition of the journal Nature, they report that the dinosaur could not possibly have reached the near-highway speeds other scientists had believed.

Though they do not include it in their study, Hutchinson says T. rex probably lumbered along, not at 45 mph, but at 10 mph. In other words, a good sprinter could have gotten away from it.

The new report will now face the skeptical eye of other scientists, but many applaud Hutchinson and Garcia for their rigor. "People had these things as track-meet speedsters out there running along, tearing up everything in sight," says Mark Norell of the American Museum of Natural History in New York, "but that's really biomechanically impossible."

Dinosaur King Meets Super-Chicken

How could our image of T. rex change so drastically? Hutchinson says it's all a matter of scale.

Many assumptions about dinosaurs, he says, were based on what scientists know about their modern-day descendants, such as birds and reptiles. But dinosaurs were many times larger. For a 13,000-pound Tyrannosaurus to be able to run at all, its legs would have had to be ridiculously large.

That's because, even if one could double the size of an animal, one couldn't double the strength of its bones and muscles.

For comparison, Hutchinson and Garcia did a computer model of a chicken, which scampers around easily because it weighs 7 pounds. They found that if one could grow the chicken to 13,000 pounds, it would need leg muscles twice as big as the rest of its body.

"A 13,000-pound human could not run, and probably, based on what we found with our chicken, could not walk, or even stand," says Hutchinson.

So maybe the movies have had it wrong, and T. rex was a slowpoke.

No matter — the dinosaurs it killed for lunch were probably even slower.