for National Geographic News
That well-imagined nightmare in which a bloodthirsty Tyrannosaurus
rex is chasing the family car down a lonely road in the red-rock
desert as the children scream and the gas gauge hovers on empty and the
dinosaur gnashes at the rear bumper is just that: a bad dream. T.
rex was a slowpoke.
The most feared and revered of the dinosaurs did not have the leg strength to run very fast, if at all, according to a computer model developed by two experts in the mechanical movements of living creatures.
The model suggests the Cretaceous landscape was filled with large, lumbering creatures that any human with a fast car or bike or maybe even a quick sprint could outpace.
The research, reported in the February 28 issue of Nature, brings the discipline of biomechanics to the long and at times contentious debate over just how fast the largest of the largest creatures ever to roam Earth could run.
"Large animals need a larger fraction of their body mass as leg muscles in order to do the same things that smaller animals can do, but there is a limit to how large that fraction can be," said John Hutchinson, co-author of the paper and a postdoctoral research fellow in the Biomechanical Engineering Division at Stanford University in Palo Alto, California.
At 13,228 pounds (6,000 kilograms), T. rex was over that limit, he said. So, too, were some of T. rex's potential prey, such as Edmontosaurus (large duckbill) and Triceratops (horned dinosaur).
Consequently, Hutchinson and his colleague Mariano Garcia, a mechanical engineer in Ithaca, New York, concluded that the large dinosaurs must have lumbered around at a much slower pace than suggested by some paleontologists and depicted in popular movies.
A classic scene in the movie Jurassic Park, for example, shows T. rex chasing a car that's traveling about 45 miles (72 kilometers) an hour. According to Hutchinson and Garcia's model, that's impossible. Eighty-six percent of T. rex's body mass would have to be leg muscle for the behemoth dinosaur to run that fast.
No creatures can have most of their body weight in their legs. It doesn't leave enough room for a skeleton, muscles, and other body parts.
"An animal cannot be made 100 percent out of leg muscle," said Hutchinson. "In fact, muscle of any kind normally is about one half of an animal's mass, and supportive leg muscle is usually only 5 to 20 percent of an animal's mass."
Need for Balance
The model designed by Hutchinson and Garcia uses equations from physics and biology to calculate the amount of leg muscle an animal needs to remain balanced during fast two-legged running.
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