Long thought of as big and dimwitted, the T. rex might owe its perch as king of the Cretaceous to its brains as much as its jaws and giant teeth.
That’s a level of brain cells similar to that in baboons, potentially making theropods — a group of vicious, two-legged and fast-running dinosaurs that included tyrannosauruses and velociraptors — the “primates of their time,” according to Suzana Herculano-Houzel, a neuroscientist and biologist at Vanderbilt University who wrote the paper.
“What if the asteroid hadn’t happened?” Herculano-Houzel said, referring to the cosmic collision thought to have driven most dinosaurs to extinction. “That’s a whole other world that would have been terrifying.”
The new research builds on a growing body of evidence suggesting the Tyrannosaurus rex was more than just a big brute. Rather, it appears to have been a social animal that worked in packs.
The soft tissue that made up dinosaurs’ gray matter rotted away eons ago. So Herculano-Houzel looked at T. rex’s bony brain cases and compared them to the skeletons of its living cousins: the birds.
It's officially news: T. rex had baboon-like numbers of brain neurons, which means it had what it takes to build tools, solve problems, and live up to 40 years, enough to build a culture! Paper is just out in J Comp Neurol. Reality was actually MORE terrifying than the movies! pic.twitter.com/6HafJVHQlk— Suzana Herculano-Houzel (@suzanahh) January 5, 2023
Extrapolating from emus and ostriches, Herculano-Houzel estimated the T. rex’s cerebrum had as many as 3 billion neurons, comparable to a baboon’s brain. Another terrifying carnivorous dinosaur called the Alioramus, meanwhile, had over 1 billion, similar to a capuchin monkey.
If the T. rex’s cognition approached that of a baboon’s, the dinosaur may have been capable of using tools and passing down knowledge through generations, Herculano-Houzel said.
“The overall study is an important step in understanding the evolution of the structure and function of the modern bird brain,” said Amy Balanoff, an evolutionary biologist at Johns Hopkins University not involved in the study.
Other research that chips away at the childhood image of the T. rex as a scaly, solitary monster involves mass burial sites found in Utah, Montana and elsewhere, suggesting the carnivores moved in groups like wolves. The remains of other male theropods have been found guarding clutches of eggs, a social behavior seen in modern birds.
Paleontologists even suspect tyrannosauruses had feathers — and are hunting for the fossil evidence.
Herculano-Houzel’s analysis hinges on treating theropods as a separate, warm-blooded group instead of lumping T. rex and its cousins with the rest of the dinosaurs.
Past researchers, she said, used to “take all dinosaurs together and throw them in the blender.”
Balanoff said she would like to see future research with updated fossil measurements. She also called the notion of the T. rex forming cultures a “really fascinating idea” but added, “I don’t know that we’re quite there yet in being able to make this prediction.”
“That being said, I welcome the positing of big ideas to drive science forward,” Balanoff said.
Now that paleontologists know to look for it, perhaps they will find more evidence of T. rex’s rich social lives, Herculano-Houzel said.
“If they were hunters, maybe you find evidence of them hunting in groups, using some sort of social communication. If you have no reason to expect that, you’re not going to look for that evidence.”
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