Tyrannosaurus rex walked surprisingly slowly, new study finds
Published Wednesday, April 21, 2021 8:27AM EDT
A cast of a Tyrannosaurus rex discovered in Montana greets visitors as they enter the Smithsonian Museum of Natural History in Washington on April 15, 2014. (AP / J. Scott Applewhite)
Tyrannosaurus rex was a fearsome predator, but it sure wasn't a particularly fast mover. In fact, most humans could easily keep up with the dinosaur without breaking a sweat.
T. rex would have covered just under 3 miles in an hour -- a speed similar to that of humans and many other animals -- at its preferred walking speed, according to new calculations by Dutch paleontologists. However, this pace is slower than other estimates of the tyrant lizard king's walking speed.
When they have no reason to run, most animals -- including humans -- have a natural walking speed that minimizes the amount of body energy spent.
Earlier estimates had not taken fully into account the role of the T. rex's tail -- which makes up more than half its length -- when crunching the numbers, said Pasha van Bijlert, lead author of a new study on T. rex locomotion published in the journal Royal Society Open Science on Tuesday.
"Animals tend to prefer walking speeds at which, for a given distance, energy cost is minimal. They do this choosing specific step rhythms at which their body parts resonate. Since the entire tail of T. rex is suspended by ligaments, which behave like rubber bands, we reconstructed this tail to investigate at which step rhythm the tail of T. rex would resonate," said van Bijlert, a graduate student in paleo-biomechanics at Vrije Universiteit Amsterdam, via email.
"The entire tail, by our reconstruction at almost 1,000 kilos, was really just a mass supported by a rubber band and with every step it would slightly bounce up and down. With the right rhythm you get a lot of movement for very little effort."
The research team calculated a step rhythm from a computer model of a T. rex tail, based on Trix, an adult 12-meter-long (39-foot-long) T. rex fossil at the Naturalis Biodiversity Center, a museum of natural history and research center in the Netherlands. The scientists then multiplied the step rhythm by the step length found in fossilized tracks for an estimated baseline walking speed of 2.86 miles per hour.
Other methods, van Bijlert said, mainly focus on calculations based on the legs and hips. They certainly play a crucial role in estimations, but calculations based only on these parts of dino anatomy may lead to inaccurate results. That's because T. rex and many other dinosaurs had unique tails that aren't found with any other living animals today.
SIMILAR TO WALKING SPEED OF ANIMALS TODAY
Understanding how a top predator like T. rex moved can help paleontologists better understand dinosaur behavior and ancient ecosystems, answering questions like: How much food did it need to move that huge body at that speed? How far would it have ranged to find prey?
For instance, a T. rex would use its preferred walking speed when walking toward a water source, said van Bijlert. "It may also give you an idea of what types of distances it may traverse when looking for food."
He did not estimate the T. rex's maximum speed in this research but plans to do so using the same method in the future.
Other studies have investigated the dinosaur's running abilities and suggested it could have a top speed of between 12 miles per hour (20 kilometers per hour) and 18 miles per hour (29 kilometers per hour) -- any faster and the bones may have shattered.
John Hutchinson, a professor of evolutionary biomechanics at the Royal Veterinary College in London said that the role played by tails had been a neglected topic in dinosaur locomotion studies.
"What speed giant tyrannosaurs might have normally walked at hasn't been a big question for many studies, but it is still an interesting question. The approach used here is complementary to fancier muscle-based simulation studies and, in a way, to data from fossil footprints," he said in an email.
"This study covers some new ground in a clever way with an original model. It's interesting and would be useful to integrate with and compare with other approaches in the future."
What surprised van Bijlert the most about the research was that the T. rex walking speed the team found was similar to that of a diverse range of animals alive today.
"Humans, ostriches, horses, elephants, giraffes, gnus and gazelles all have a remarkably close distribution in preferred speeds (about 2.2 - 3.1 mph). So this includes both two- and four-legged animals, and also both relatively small and large animals," he said via email.
"The interesting thing is that our new method predicts slower walking speeds for T. rex than other methods, but the speed that we find is closer to many animals living today."