Actually, You Could Have Outrun a T. rex

Contrary to popular belief, the tyrant lizard king was not built for speed. Instead, the mighty Tyrannosaurus rex was typically restricted to a brisk walk, according to a rigorous new computer model.

The top speed of a T. rex has been a long-standing debate among paleontologists. Previously, the best estimates indicated that the large lizard could run between 11 and 33 miles an hour.

That means that in an imagined race between a person and the iconic dinosaur, there was the possibility that a T. rex could outrun the world’s fastest human, who clocks in around 27 miles an hour.

Now, paleontologist William Sellers from the University of Manchester and his colleagues have crunched the numbers using even more comprehensive information.

According to their results, published this week in the journal PeerJ, the lower end of the estimate is more accurate: T. rex probably could only reach around 12 miles an hour. Any faster, and its bones would have shattered.

Slow and Steady

Decades ago, paleontologists would point to individual parts of the T. rex skeleton and say it proved that the dinosaur was either fast or slow. Superficially comparing T. rex limbs to ostrich limbs, for instance, it stood to reason that the 40-foot-long dinosaur could have been quick. (Here’s what it would feel like to pet a T. rex.)

With the advent of more complex biomechanical models, though, scientists can get much closer to an answer. (Also see our best look yet at a tyrannosaur’s face.)

“You need to put all parts together to get a full picture. Just looking at morphology alone won’t get you there,” says John Hutchinson, an evolutionary biomechanics expert at the Royal Veterinary College in London who was not involved in the study.

One of the new factors taken into account in this model was bone stress. A bone can only handle so much pressure while running before it shatters. Sellers and his team developed their new model using the total body weight of a T. rex—around seven tons—along with the mechanical properties of bone.

This is a slightly different approach than has been used in the past, Hutchinson says.

“This study uses the assumption that at maximum speed, the muscles weren’t the limiting factor,” he says. “At the previously proposed top speed, T. rex would have shattered foot bones, according to this model.”

As Sellers says in the study, T. rex was not one of the more “athletic” dinosaurs on the Cretaceous landscape—and that’s not a huge surprise to most paleontologists.

“The movie image of T. rex is wrong,” says Stephen Brusatte, a paleontologist at the University of Edinburgh who was not involved in the study. “Paleontologists have realized this for over a decade now, and this new study drives it home by providing the most sophisticated computer modeling studies yet.”

Still, people take any demotion of a “celebrity dinosaur” like T. rex pretty seriously, Hutchinson notes. “It has to be fast or else it won’t be cool. People have an emotional tie to it.”

Brusatte agrees, adding that this study will throw more doubt on dinosaur lovers’ favorite cinematic moments.

“No way T. rex could have chased down that Jeep in Jurassic Park if it was going at highway speeds,” he says. “Maybe if it was in first gear, but even that's a big if.”

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