How Intelligent Was T. Rex? Scientists Suggest the Dinosaurs Were Like ‘Smart, Giant Crocodiles’

A new paper refutes the idea that T. rex was as brainy as a baboon, furthering the debate on the extinct reptile’s intellect

Skeleton of T. rex, focused on its head
Scientists are at odds about how intelligent T. rex was. Sage Ross via Wikimedia Commons under CC BY-SA 3.0

How intelligent was Tyrannosaurus rex?

Paleontologists and other researchers have long been intrigued by this question—and it’s a difficult one to answer. While scientists have plenty of fossilized bones to study, they don’t have many dinosaur brains.

Last year, Vanderbilt University neuroscientist Suzana Herculano-Houzel published a paper estimating that dinosaurs like T. rex had three billion neurons in their brains—more than a baboon. To Herculano-Houzel, this suggested T. rex was much smarter than previously assumed—intelligent enough to use tools, solve problems and even pass down knowledge through generations.

The study was controversial at the time, with some researchers publicly expressing their skepticism. But now, new research officially refutes the findings: A paper published this month in the Anatomical Record proposes that T. rex was only as smart as the reptiles of today.

“The possibility that T. rex might have been as intelligent as a baboon is fascinating and terrifying, with the potential to reinvent our view of the past,” Darren Naish, a co-author of the new paper and a paleozoologist at the University of Southampton in England, says in a statement. “But our study shows how all the data we have is against this idea. They were more like smart, giant crocodiles, and that’s just as fascinating.”

The new study’s co-authors argue that Herculano-Houzel’s neuron estimates were wrong, because they were based on faulty assumptions about dinosaur brains. To come up with her estimate, Herculano-Houzel compared T. rex to some of its living relatives—birds like emus and ostriches, reported the Washington Post’s Dino Grandoni in January 2023.

While birds are descendants of theropods—the same group of dinosaurs that T. rex belonged to—theropods themselves were reptiles. And, as such, their skulls were probably more like those of today’s living reptiles than birds, the new study’s authors argue. By that logic, T. rex skulls likely contained a large amount of cerebrospinal fluid—and not very much brain tissue.

“The first time I dissected an alligator brain, I took the top of the skull off and I went, ‘Where is the brain?’” says study co-author Doug Wylie, a neurophysiologist at the University of Alberta, in a statement. “Because there is this big space in there.”

In addition, reptile brains have lower neuron density than bird or mammalian brains, the authors write. The number of neurons also tends to scale with body size—so, even if T. rex did have as many neurons as a baboon, that does not mean the dinosaur’s intelligence was on par with a primate’s. Larger animals simply need more neurons for basic biological functions.

“The T. rex weighed seven tonnes and the baboon weighs 40 kilos,” says study co-author Cristian Gutierrez, a neuroscientist at the University of Alberta, to the Canadian Press’ Bob Weber. “It’s not the same, right?”

Beyond that, the number of neurons does not necessarily indicate a species’ intelligence, he adds. Eurasian magpies, for example, have only about 400 million neurons, but they’re highly intelligent creatures that can work in teams, play games, use tools and imitate human speech. Giraffes, meanwhile, have two billion neurons and do none of those things.

“Neuronal counts really are comparable to the storage capacity and active memory on your laptop, but cognition and behavior is more like the operating system,” says study co-author Thomas R. Holtz, Jr., a vertebrate paleontologist at University of Maryland, College Park, to the Los Angeles Times’ Corinne Purtill. “Not all animal brains are running the same software.”

Herculano-Houzel, for her part, stands by her work—and argues that “it comes down to whether theropods like T. rex were already more similar to modern birds like an ostrich or reptilian-like in their brain [to] body size relationship,” she writes in a post on X.

But, she tells the L.A. Times in an email, she’s happy that her “simple study using solid data published by paleontologists opened the way for new studies.”

“Readers should analyze the evidence and draw their own conclusions,” she adds. “That’s what science is about!”

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