I’m a paleontologist. I’ve made a career out of studying Tyrannosaurus rex, and I’ve described and named a few of its closest relatives. But when I think of T. rex, the first image to come to mind is the iconic scene in Jurassic Park, in which a blood-lusting rex chases down a Jeep at highway speeds, an injured Jeff Goldblum peeking out of the back window in terror.
That moment of movie magic has so permeated pop culture that I can’t escape it. And I’m not alone. One of the most common questions I’m asked when visiting schools or giving public talks is whether that Jurassic Park Jeep chase could actually happen. No doubt, T. rex was big, T. rex was fierce, T. rex was smart. But was it really that fast?
Two studies published in July suggest the answer is “no.” Far from being a speedster, it seems the King of Dinosaurs could barely even break into a jog.
When Jurassic Park was released in 1993, the idea of a turbo-charged T. rex was completely plausible. A few decades earlier, paleontologists had begun to reimagine dinosaurs as active and energetic creatures—much more similar to today’s birds than reptiles. Some scientists argued that big meat-eaters like T. rex could whizz about at 45 miles-per-hour or so. That was the vision that enchanted Michael Crichton and Steven Spielberg, making its way into Jurassic Park.
What the moviemakers probably never realized, however, was that there was little evidence that T. rex could run fast. But even if they did recognize this dirty little secret, they probably wouldn’t have been too concerned. After all, T. rex has been dead for 66 million years. We can’t observe a rex in the wild and clock it with a stopwatch, or bring it into the lab and put it on a treadmill. So how could we possibly know how fast it was?
To paraphrase Jeff Goldblum’s character, science finds a way.
In the early 2000s, right around the time Jurassic Park III made its inglorious debut in theaters, John Hutchinson made the first serious attempt to study the locomotory behaviors of T. rex and predict its speed. Hutchinson used computer models—then a novel technique for paleontologists—to show that T. rex would have needed laughably huge leg muscles—comprising an absurdly impossible 86% of total body mass—to run quickly (at, say, more than 20 miles per hour). And even if rex somehow could force its muscles into overdrive and accelerate to running speeds, its hefty seven-ton bulk would have made it liable to tip over, like a race car taking a corner too quickly.
Hutchinson’s vision of T. rex became widely accepted by most of my fellow paleontologists. But like most arguments sequestered in the peer-reviewed literature, it was nearly powerless against the crush of pop culture. When Jurassic World raked in hundreds of millions of dollars in the summer of 2015, audiences still gawked at a speed-burner T. rex.
Perhaps two new studies will change that. They use wildly different methods, but both agree with Hutchinson.
The first, a paper published in the journal PeerJ by paleontologist Bill Sellers and his team, builds on Hutchinson’s work by utilizing the latest and most comprehensive computer models. They began with a high-resolution, three-dimensional laser scan of one of the best preserved and most complete T. rex skeletons ever found. Then, they digitally added muscles and other soft tissues, by locating all of the small bumps and projections on the bones where these tissues attach and comparing with living dinosaur relatives (like birds and crocodiles) to make sure they were putting the muscles in the right places. Finally, they used a variety of computer simulations to put their fully fleshed-out rex through all sorts of walking, jogging, and running routines. The result was clear: T. rex could only move at a walking gait, of about 12 miles per hour (20 kilometers per hour). If it tried to run at Jurassic Park speeds, its foot bones would have shattered.
The second study, published in Nature Ecology and Evolution by a team of biologists led by Myriam Hirt, took a much different approach. To understand T. rex, they turned to modern animals. They compiled a database of the top speeds and body sizes of nearly 500 living species and found a general relationship between these two basic metrics, which means that by simply knowing the mass of T. rex (seven tons) they could predict its top speed at about 18 miles-per-hour (29 kilometers-per-hour).
Yes, the studies differ slightly in detail, with the Sellers computer models suggesting a lower speed than the Hirt equation. But this difference is minor, and is explained by the different methodologies: one uses specific anatomical models of T. rex; the other is a panoramic study of living species that looks at top speeds (and not average or “normal” speeds). In the grand scheme of things, the studies are remarkably congruent with each other, and with Hutchinson’s work. T. rex could not run fast.
So what was life like for T. rex as a living, breathing animal? We have to drop the assumption that rex was a big, mean dinosaur version of a cheetah. It was not a pursuit predator that would chase down its prey over long distances. Most of the time it could merely walk, or maybe enter into a slow jog before quickly exhausting itself. When hunting, T. rex relied on its brute strength and its keen intelligence and senses, not its speed.
That also means that the Jurassic Park rex couldn’t have caught up with the Jeep, at least once it got past first gear. Jeff Goldblum would have been okay—he probably would have laughed as the rex pathetically tried to keep pace by power walking, as the Jeep sped off into the rain. But that just doesn’t have the same cinematic drama, now does it?