FRIDAY, March 8, 2002 (HealthDayNews) -- Tyrannosaurus rex may have been a towering "terrible lizard," but it certainly wasn't a terrific runner.
That's the verdict of two American scientists who used computer modeling to calculate that the dinosaur's much-touted top speed of 45 mph was probably a lot closer to 10 mph.
The new finding, published in Nature, reveal that for T. rex to reach speeds of 45 mph, its leg muscles would have had to make up an impossible 86 percent of its body mass.
Stephen M. Gatesy, an associate professor of ecology and evolutionary biology at Brown University, is familiar with the study. He says it's the first time anyone has approached the question of how fast a dinosaur could run using a computer model and biological knowledge of both skeletal and muscle systems.
The idea for the study developed when lead investigator John R. Hutchinson, who is now a post-doctoral researcher at Stanford University, was reading books and articles on dinosaurs and locomotion. They suggested that T. rex and other large dinosaurs could run 45 mph or faster.
However, Hutchinson wasn't convinced. When he started graduate school at the University of California-Berkeley, he and his colleague, Mariano Garcia, decided to create a simple biomechanical computer modeling system that would tell them how much muscle mass a T. rex would have needed to run at those speeds.
First, they tested the model on living animals, including chickens, humans and alligators. Chickens and humans have roughly twice the amount of leg muscle required for running on two legs; alligators have only half the required leg muscle, which is why they can't get up and sprint on two legs.
Then the researchers turned to T. rex, and tried to determine the minimum amount of muscle mass required for the massive dinosaur to run 45 mph.
According to the model, the amount of muscle needed to run increases faster than overall body mass, and T. rex would have needed supportive muscles in its legs amounting to 86 percent of its body mass to do that.
At that rate, the dinosaur wouldn't have enough weight left over for bones or other crucial anatomy.
"The amount of muscle that a tyrannosaur would have needed to run at about 45 mph is far more than the body could've really contained," Hutchinson says.
"Just to move quickly, the forces that it would have experienced at a really high speed were too much. So, it had to slow down to at least 25 mph and probably much slower. I think the 10 mph estimate is more realistic," he says.
"I think Tyrannosaurus was near a limit of what an animal can be and still move around reasonably quickly," Hutchinson adds. "Ten miles an hour is still a fast speed. That's a little bit slower than the average human can run, but it's still pretty fast."
Hutchinson points out the dinosaur's 10-foot-long legs would have given it a sizable stride. "So, just by swinging its legs slowly, it could have covered a lot of ground quickly," he explains.
To further show that size limits speed, Hutchinson and Garcia dissected a 7-pound chicken, taking measurements including leg length and the angle of various joints. Then, they scaled the chicken's measurements up to the size of an adult T. rex and created a 13,228-pound chicken.
"We found that a giant chicken would need twice as much muscle as it actually had body mass," Hutchinson says. "There's no way it could have fit even half as much muscle as it needed into its entire body in order to run quickly."
"Giant chickens are an impossibility," Hutchinson adds, noting when poultry breeders try to create larger chickens with bigger breasts or legs, the animals have problems walking.
Gatesy says this approach to examining movement and function in animals represents the future of studying extinct life forms.
"If you're really interested in paleobiology, it's got to have the biology in there," he says.
Hutchinson is currently developing more complex locomotion computer models at Stanford to look at the walking patterns of other dinosaurs, including velociraptors and triceratops, as well as living animals.
What To Do
You can visit Hutchinson and Garcia's Web site to find out more about their research.
For more information on T. rex, check out the
University of California-Berkeley or the T. rex at the Smithsonian National Museum of Natural History .
