In December 2022, Vanderbilt University neuroscientist Suzana Herculano-Houzel published a paper that caused an uproar in the dinosaur world.

After analyzing previous research on fossilized dinosaur brain cavities and the neuron counts of birds and other related living animals, Herculano-Houzel extrapolated that the fearsome Tyrannosaurus rex may have had more than 3 billion neurons — more than a baboon.

As a result, she argued, the predators could have been smart enough to make and use tools and to form social cultures akin to those seen in present-day primates.

The original "Jurassic Park" film spooked audiences by imagining velociraptors smart enough to open doors. Herculano-Houzel's paper described T. rex as essentially wily enough to sharpen their own shivs. The bold claims made headlines, and almost immediately attracted scrutiny and skepticism from paleontologists.

In a paper published Monday in "The Anatomical Record," an international team of paleontologists, neuroscientists and behavioral scientists argue that Herculano-Houzel's assumptions about brain cavity size and corresponding neuron counts were off-base.

True T. rex intelligence, the scientists say, was probably much closer to that of modern-day crocodiles than primates — a perfectly respectable amount of smarts for a therapod to have.

"What needs to be emphasized is that reptiles are certainly not as dim-witted as is commonly believed," said Kai Caspar, a biologist at Heinrich Heine University Düsseldorf and co-author of the paper. "So whereas there is no reason to assume that T. rex had primate-like habits, it was certainly a behaviorally sophisticated animal."

Brain tissue doesn't fossilize, and so researchers examine the shape and size of the brain cavity in fossilized dinosaur skulls to deduce what their brains may have been like.

In their analysis, the authors took issue with Herculano-Houzel's assumption that dinosaur brains filled their skull cavities in a proportion similar to bird brains. Herculano-Houzel's analysis posited that T. rex brains occupied most of their brain cavity, analogous to that of the modern-day ostrich.

But dinosaur brain cases more closely resemble those of modern-day reptiles like crocodiles, Caspar said. For animals like crocodiles, brain matter occupies only 30% to 50% of the brain cavity. Though brain size isn't a perfect predictor of neuron numbers, a much smaller organ would have far fewer than the 3 billion neurons Herculano-Houzel projected.

...continued

©2024 Los Angeles Times. Visit at latimes.com. Distributed by Tribune Content Agency, LLC.