Tyrannosaurs may have hunted in packs like wolves, a new study says, undermining the idea they were solitary predators

• New evidence suggests that tyrannosaurs hunted as a pack animal.
• The dinosaur remains were found in the Grand Staircase-Escalante National Monument in Utah.
• Scientists had previously thought that the tyrannosaurs' brains were too small for this kind of complex behavior.
• See more stories on Insider's business page.

Tyrannosaurs were probably social animals who hunted in packs, according to research from the University of Arkansas published Monday.

The research challenges a common theory that the huge lizards were solitary hunters who chased down prey alone, perhaps because they were too stupid to cooperate.

The tyrannosaur category includes the famous Tyrannosaurus rex as well as similar-looking carnivores likes the Albertosaurus and Gorgosaurus.

"A lot of researchers feel like these animals simply didn't have the brain power to engage in such complex behavior," Alan Titus, a paleontologist for the Bureau of Land Management who led the research, told reporters in an online briefing, The Washington Post reported.

But this research suggest that the animals hunted in packs, like wolves, or like the velociraptors hunting together in "Jurassic Park."

The scientists looked at the remains of four or five tyrannosaurs aged roughly between 2 and 44 years of age, found in Utah in the Grand Staircase-Escalante National Monument.

This was the first tyrannosaur mass death site found in the southern US, The Post reported.

The results of this investigation, published in the peer-reviewed journal Peer J on Monday, suggest that the dinosaurs died while hunting together, challenging the idea that they only hunted alone.

An artist representation of the dinosaurs, in this tweet from the Bureau of Land Management Utah, shows how they might have died:

-Bureau of Land Management Utah (@BLMUtah) April 19, 2021

Grand Staircase-Escalante national monument is one of two Utah monuments that President Joe Biden pledged to restore as part of his campaign.

The fossils "are national treasures," Titus said, The Guardian reported. "They're part of the story of how North America came to be and how ultimately we came to be."

"This is a cool analysis," Professor Mike Benton, a professor of vertebrate paleontology at the University of Bristol, UK, told Insider in an email. "They have a smart method that makes sense, and the results are plausible," he said.

"In a way, it was a question we never asked," Benton said. Until recently, "it was fanciful even to try to estimate how many dinosaur individuals existed on Earth," Benton said.

A separate study, also out this week, found that 2.5 billion fully grown T. rexes roamed the Earth over the 2.5 million years that the species was around, Insider's Aylin Woodward reported.

The site where the remains were found was nicknamed Rainbows and Unicorns Quarry because of the abundance of turtle, fish, alligator, and dinosaur remains found there.

Its discovery was sheer luck. Titus and a group of volunteers went to the site in 2014 to look at the turtle remains.

During a freak storm, they were stranded. But they were rewarded when the heavy rain uncovered a T. Rex bone.

The tyrannosaurs in the Rainbows and Unicorn quarry are thought to come from the Teratophoneus species, The Guardian reported.

The findings build on the discovery of other sites where bones were found huddled together, the scientists said in a statement.

One was in Canada, where 12 individuals tyrannosaurs of the Albertosaurus species were found in Dry Island Buffalo Jump park.

"This must be reflecting some sort of behavior and not just a freak event happening over and over again," Titus told reporters.