Not so fast, Tyrannosaurus rex! A recent study that said theropod dinosaurs such as T. rex were speedy creatures (see "Run, Dinosaur, Run," 2/8) has been stopped in its tracks. Some scientists aren't so sure T. rex had the legs to even chase down live prey.
Last week, scientists argued that T. rex was a slow mover, lumbering along at 10 miles an hour. They used computers to calculate how much muscle in relation to its size an animal would need in order to move fast.
The scientists said that a 6-ton T. rex would need giant leg muscles—taking up about 80% of its body mass—to hit high speeds. "Things have a harder time moving as they get bigger," said Mariano Garcia in the journal Nature. Still, the debate over T. rex's speed promises to run on and on.