"We clocked the T. rex at 32 miles an hour," John Hammond, played by Richard Attenborough, casually informs his guests in Jurassic Park. Later, when the T. rex inevitably breaks out of her paddock, this speed limit is put to the test as the intimidating predator bears down on a Jeep in one of the most iconic chase scenes in film history.
This popular image of light-footed tyrannosaurs running after targets—which was recently rehashed in Jurassic World—has defined our view of how this extinct carnivore looked and lived.
But according to two unrelated studies published this week, in the journals Nature Ecology & Evolution and PeerJ, T. rex could not have come close to running 32 miles per hour. In contrast to its sporty depiction in movies, this animal appears to have been a bonafide slowpoke, sidling along at estimated top speeds of 12 to 17 miles per hour (20 to 29 kilometers per hour). By contrast, Usain Bolt can run nearly 28 miles per hour, cheetahs can top 60 miles per hour, and 1992 Jeep Wranglers, like those used in Jurassic Park, can accelerate to over 90 miles per hour.
William Sellers, a professor at the University of Manchester's School of Earth and Environmental Sciences, led the PeerJ study, which combines multi-body dynamics simulations, machine learning algorithms, and skeletal stress analysis to create "the most anatomically complete reconstructions" of T. rex locomotion yet, according to the authors.
Simulated reconstruction of T. rex walking gait. Image: 2017 Sellers et al.
Using these data-rich simulations, Sellers and his colleagues found that classic running gaits, involving periods where both feet are off the ground, would have risked breaking T. rex's bones , These huge carnivores weighed as much as nine tons (18,000 pounds), and while they may have dialed their walking gait up to around 12 miles per hour, Sellers' team argues that they couldn't push far beyond that pace. That upper limit has major implications for how researchers understand and interpret these giants' evolution and behavior.
" T. rex had to eat and these results suggest it couldn't catch fast-running prey by chasing it down," Sellers told me over email. Instead, he said, tyrannosaurs may have targeted equally large, slow herbivores, like hadrosaurs (duck-billed dinosaurs), or used ambush attacks to ensnare smaller animals. When scavenging for dead meat, T. rex could have also used its bulk to scare off smaller corpse-feeders, a solid tactic that doesn't require fleet feet.
This vision of a leisurely paced T. rex is further corroborated by research into the relationship between animal sizes and speeds, led by Myriam Hirt, a zoologist at the German Centre for Integrative Biodiversity Research in Leipzig, which was published in Nature Ecology & Evolution on Monday.
Hirt and her team generated a scaling model that explains why abnormally large size is often a trade-off for slower speeds in nature. Mid-scale animals like cheetahs, marlins, and falcons outpace their giant counterparts on land, in the sea, and in the air, and the same pattern likely held true for dinosaurs: Small species like velociraptors would have been much faster than colossal tyrannosaurs, which Hirt and her colleagues suggest topped out around 17 miles per hour.
This conclusion is not exactly new—a major 2002 Nature study by John Hutchinson suggested that T. rex's muscular buttocks were more in line with power-walking than running. Since then, more sophisticated computer simulations have allowed for increasingly precise estimates of T. rex's speedometer range, supporting an emerging consensus that this fierce predator was likely, at heart, an ambler.
Curbing the speed limit of T. rex might seem to defang the animal's onscreen presence somewhat, but Sellers points out that this famous meat-eater would still have some real bite, even at reduced speeds.
" T. rex hatch out of eggs the size of footballs, and then grow over the space of 20 or so years," he told me. "An adolescent T. rex would be just the right size to think that a human was definitely worth the effort and would be small enough that it probably could run reasonably fast. I don't think wandering around in the [Montana fossil bed] Hell Creek during the Cretaceous would have been particularly safe."
Even so, it remains to be seen if these assessments into T. rex's running abilities, or lack thereof, will alter the animal's portrayal as an agile sprinter in pop culture. Probably not, given that most cinematic T. rexes still don't have feathers.
Get six of our favorite Motherboard stories every day by signing up for our newsletter.