T-Rex Couldn’t Run—Doing So Would've Broken Its Legs

T-Rex
Tyrannosaurus Rex exhibit at the Natural History Museum of Leiden, Netherlands. Dean Mouhtaropoulos/Getty Images

Updated | Tyrannosaurus rex could not run, scientists now believe, in direct contrast to previous research. Instead, the dinosaur probably walked along at a fairly slow pace, eating slow-moving sauropods rather than chasing after fast-moving prey. 

Previous research had suggested T-Rex could clock speeds of up to 45 miles per hour and the new estimates paint a far less fearsome image of one of the Cretaceous period's apex predators.

The debate over T-Rex’s running abilities has raged for decades. Following the initial discovery of the species in the 1800s, T-Rex was often depicted as being a fast-moving creature. In the 1980s and 90s, several studies reinforced this image, based on anatomical research that indicated a very fast running speed and a high level of athleticism.

But not all scientists agreed, and more recent research using biomechanical approaches has indicated the predator moved at far slower speeds. Studies published over the last 15 years have favored the idea that T-Rex could not run at all.

In a study published in Peer J Tuesday, a team from the University of Manchester, U.K., demonstrated how a T-rex would move. They used two separate biomechanical approaches to create a computer model simulating how T-Rex would run, if it could. Because their model combined different aspects of bodily analysis, including the stress placed on the skeleton and how its body would move anatomically, the team believe the picture produced is a more accurate depiction of T-Rex’s gait.

Their findings show that not only was the species unable to run, but it could not even walk very fast. If it were to run, it would have buckled under its own weight and broken its legs, they found. They believe T-Rex’s maximum speed peaked at around 7.7 meters per second, or just over 17 miles per hour (mph). To put that in perspective, Usain Bolt, during the 100-meter sprint, has clocked speeds of over 27 mph.

This finding forces a rethink of T-Rex’s hunting style, as it would not have been able to pursue prey. It also suggests that other, similar sized and shaped dinosaurs—such as Giganotosaurus, Mapusaurus, and Acrocanthosaurus—would not have been able to run.

“We present a new approach that combines two separate biomechanical techniques to demonstrate that true running gaits would probably lead to unacceptably high skeletal loads in T-Rex,” study leader William Sellers said.

Tyrannosaurus rex is one of the largest bipedal animals to have ever evolved and walked the Earth. So it represents a useful model for understanding the biomechanics of other similar animals. Therefore, these findings may well translate to other long-limbed giants so but this idea should be tested alongside experimental validation work on other bipedal species,” he added.

The team say a slow-moving T-Rex likely had a less athletic lifestyle than previously thought—a suggestion that could alter our view of how T-Rex’s size and shape changed as it got older. It is thought its torso got longer and heavier as it got older, while the limbs got shorter and lighter, meaning younger individuals were more agile.

Commenting on the study, David Martill, professor of ​palaeobiology at the University of Portsmouth, U.K., says the findings are “very interesting” and that there is “no reason” to suppose the scientists are not right.

“It does seem to show that things slow down a bit as these apex predators get older, and that we need to think about how their ecology changed during their own lifetime,” he tells Newsweek. “Baby T-Rex may well have run around at terrific speed eating anything small that moved and would go down its gullet, but as it got older, so this changes, until eventually it was of a size capable of despatching large sauropod dinosaurs.

“As the sauropods were probably slow, there was little need for T-Rex to run, and a leisurely walk was all that was needed to catch its prey. Consequently, its skeleton was engineered to do just that.”

Paleontologist and evolutionary biologist Steve Brusatte adds: “The T-Rex that we see in the movies is a speedster that races down its prey—and sometimes even cars, in the case of Jurassic Park. For the last 15 years or so paleontologists have been arguing that this view is incorrect, and T-Rex was probably a lot slower. This new study adds a wealth of new evidence to that viewpoint. The computer modeling techniques applied here make it clear that T. rex was not a speed demon, and maybe was limited to walking. T-Rex was still a nasty predator, but speed wasn't one of its weapons. It relied on brute strength instead of sprinter speed.”

This story has been updated to include quotes from Steve Brusatte.