T. Rex Was Slow-Turning Plodder, Study Suggests

James Owen
for National Geographic News
June 7, 2007
Tyrannosaurus rex's fearsome reputation has taken another knock, with new research suggesting it was a slow-turning plodder.

The so-called king of dinosaurs has been buffeted in recent years by accusations of being a scavenger and a slowpoke.

Now a U.S. team suggests that T. rex also weighed considerably more than some experts had believed, took up to two seconds to turn 45 degrees, and is unlikely to have exceeded speeds of 25 miles (40 kilometers) an hour. (Related story: "Tyrannosaurus Rex Was a Slowpoke" [February 22, 2002].)

The study, led by biomechanics expert John Hutchinson while at Stanford University in California, is reported in the Journal of Theoretical Biology.

Building on previous work into the dino's biomechanics, the new findings challenge the perception that T. Rex was an athletic super-predator capable of running down fast, agile dinosaurs.

The team used a computer-modeling system to calculate the weight of a fossil specimen from the U.S. and then to estimate its running speed and turning ability, which has never been done before.

That fossil, an average-size adult, weighed between six and eight tons, and some individuals may have been as heavy as ten tons, the researchers said.

The team found the animal, hampered by a long tail and that heavy body, would have taken one to two seconds to make a quarter turn—far slower than a human.

"We now know that a T. rex would have been front-heavy, turned slowly, and could manage no more than a leisurely jog," Hutchinson, the lead study author, said.

Different Kind of Walk

Previous work by Hutchinson indicated that T. rex reached top speeds of between 10 and 25 miles (16 and 40 kilometers) an hour.

But the new study further undermines the popular notion that T. rex could reach speeds of around 45 miles an hour (72 kilometers an hour), as often depicted in movies.

Previous estimates that T. Rex weighed three to four tons were based only on the dinosaur's fossil bones, Hutchinson pointed out. But the new prediction involved over 30 different computer models.

"The method that we applied, creating a kind of computer sculpture of the body of a T. rex, takes into account the whole anatomy," he said.

Previous investigations into the biomechanics of dinosaurs have also often been based on living animals such as elephants, the research team added.

But the new research suggests T. rex walked very differently than the mammals, which use vertical, pillar-like legs. For the dinosaur to maintain its center of mass over its feet it would have needed to keep its legs bent, the team suggested.

The research team adds that its study has little bearing on the issue of whether T. rex was a scavenger or a predator.

It's a "false debate," with most experts now agreeing that the animal was both, Hutchinson said.

"If you look at living animals, pretty much anything that eats meat is both a predator and a scavenger," he added. "There's really no convincing evidence that says it was only a scavenger."

Slow Prey

Paul Barrett is a dinosaur researcher at London's Natural History Museum who was not involved with the study. He says the new research does appear to undermine the idea of T. rex as a super-predator.

"It suggests that T. rex is basically a lot slower and more lumbering than a lot of the recent views on it have been," he commented.

However, "most of the animals that T. rex would have been hunting were also large and pretty slow moving and not particularly agile. So although it wouldn't have been a particular speedy predator, that might not have been a big disadvantage," Barrett said.

"Whether or not it was running after its prey at high speeds, it would still have been pretty awesome, I think."
Hutchinson's team agrees, saying its weight and speed findings may also apply to other large dinosaurs such as Triceratops and Edmontosaurus, which T. rex is known to have eaten.

"These were also big clunky animals that clearly weren't running around at 50 miles [80 kilometers] an hour," Hutchinson said. "And why would [T. rex] need to turn quickly if it was preying on other big, relatively slow things?"

Smaller two-legged dinosaurs would probably have been able to outrun T. rex, however.

"T. rex probably didn't eat those, unless it got lucky and caught one off guard," Hutchinson said.

The environment during T. rex's day was also very different from today, Hutchinson added, and probably one where animals didn't need to be built for speed.

"I think there's a bias imposed by looking at living mammals in the Serengeti and elsewhere on open grasslands where they have a lot of space," he said.

"When T. rex lived there probably weren't a lot of huge open spaces to be charging around in at massive speeds."

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