Tyrannosaurus rex not so smart, after all

Tyrannosaurus rexes were mighty dinosaurs with massive skulls, scaly skin, foot-long teeth and tiny arms. They were terrifying carnivores, living in what’s now western North America more than 66 million years ago. T. rexes were among the deadliest of dinosaurs. But were they smart? A study in 2023 claimed that a T. rex could be as smart as a baboon. But a new study disputes that idea, asserting that T. rexes weren’t smart, after all, and behaved more like crocodiles and lizards.

The 2023 study was based on what are called neuron counts, that is, on the number of neurons in the brains of T. rex and other animals. Neuron counts have been used to gain insights into the intelligence of some species. For example, the human brain contains 86 billion neurons, with 16 billion neurons in the cerebral cortex, which plays a key role in things like attention, perception, awareness, thought, memory, language, and consciousness.

But what about T. rex?

The new study considered neuron counts, and on a re-examination of brain sizes and structures in dinosaurs. It was published in the peer-reviewed journal The Anatomical Record on April 26, 2024.

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Tyrannosaurus rex studies in 2023 vs. 2024

Tyrannosaurus rex: Big animal with sharp, yellowish teeth, and tiny arms with 2 fingers in each claw.
Animatronic Tyrannosaurus rex at the Natural History museum, London, United Kingdom. Image via Amy-Leigh Barnard/ Unsplash.

In last year’s study, associate professor of psychology at Vanderbilt University Suzana Herculano-Houzel found the T. rex had between 2 and 3 billion neurons. Herculano-Houzel said these neuron counts – comparable to those of baboons – could directly inform on the intelligence of T. rex. She suggested T. rex might be able to pass on knowledge to their young. They might even be able to use tools. Can you imagine? If the idea of a huge predator that used to walk Earth wasn’t terrifying enough, picture them hunting in packs, teaching their descendants and using tools … Goosebumps!

However, an international team of paleontologists, behavioral scientists and neurologists conducted a new study on the brain size and structure of the Tyrannosaurus rex, among other things. The team concluded that these dinos were as smart as reptiles – such as crocodiles and lizards – but not as smart as monkeys. They found the T. rex brain size had been overestimated – especially the forebrain – and that the 2023 estimates of neuron counts for T. rexes were likely way off base.

But how can we reconstruct the biology of an animal that went extinct millions of years ago? The new study doesn’t just focus on the skull of these creatures. A further analysis of the rest of the skeleton, the bone histology, fossils and the descendants of these animals were also taken into account. Team member Hady George of the University of Bristol wrote:

Determining the intelligence of dinosaurs and other extinct animals is best done using many lines of evidence ranging from gross anatomy to fossil footprints, instead of relying on neuron number estimates alone.

How to study an extinct animal?

Herculano-Houzel clearly didn’t have a T. rex brain in front of her to study. So, she analyzed the brains of evolutionary descendants of the dinosaurs, such as modern birds, reptiles and turtles. She then compared the results with fossilized brain cases of ancient lizards. She concluded that dinosaurs were as smart as monkeys, because their neuron counts were equivalent to that of some intelligent primates, such as baboons. But neuron count estimates are not a reliable guide to intelligence.

Another thing to consider is whether or not brain tissue fills the entire skull. Team member Cristian Gutiérrez-Ibáñez of the Department of Biological Sciences, University of Alberta, noted the actual brains inside T. rex skulls were much more related to modern crocodiles than birds. And it turns out that crocodiles have big skulls but they contain a significant amount of fluid and other tissue. Only 30% of a croc’s skull contains grey matter.

In addition to this, bird brains are denser, neuron-wise, than reptile brains. So, are 2 billion neurons in a small body the same as in a big body? The answer is no. A big body needs a big brain because it has a lot more body to operate. Gutiérrez said:

It’s clear larger animals need more neurons.

Are brain size and intellect connected?

According to Gutiérrez, more neurons doesn’t necessarily mean smarter. For example, giraffes also possess around 2 billion neurons, but they don’t pass on knowledge or use tools. There are other animals that are much smaller, have fewer neurons and can learn tricks (crows), teach their young (ants), repeat what they see or hear from humans (parrots or cockatiels), and even prepare funerals (magpies).

But how can we know for sure how smart T. rex was? Fossils provide some indications on how dinosaurs lived. They tell us that T. rex parents were protective of their young and lived in groups, for example. But there will always be a limitation to what we can know. Gutierrez said:

That’s the one thing that isn’t going to be fossilized … behavior.

Bottom line: We all know Tyrannosaurus rex dinosaurs: they’re huge with scaly skin, big teeth and tiny arms. But how much do we know about their brains? A new study says they weren’t quite as smart as monkeys and were more like crocodiles.

Source: The Anatomical Record. How smart was the T. rex? Testing claims of exceptional cognition in dinosaurs and the application of neuron count estimates in palaeontological research

T. rex not as smart as previously claimed, scientists find

New U of A research questions T. Rex intelligence, culture-building

May 3, 2024

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