How Smart Were Tyrannosaurus rex and Other Large Theropod Dinosaurs? | Sci.News

Tyrannosaurus rex holotype specimen at the Carnegie Museum of Natural History, Pittsburgh, the United States. Image credit: Scott Robert Anselmo / CC BY-SA 3.0.

In a study published last year, Vanderbilt University paleontologist Suzana Herculano-Houzel claimed that dinosaurs like T. rex had an exceptionally high number of neurons and were substantially more intelligent than assumed.

She claimed that these high neuron counts could directly inform on intelligence, metabolism and life history, and that T. rex was rather monkey-like in some of its habits.

"The Late Cretaceous North American theropod dinosaur T. rex is a superlative predator, being among the largest, heaviest, and most powerful (in terms of bite force) terrestrial carnivores of all time," said University of Bristol's Dr. Hady George and colleagues.

"Recently, Dr. Herculano-Houzel proposed that anthropoid primate-level intelligence should be added to T. rex's already impressive predatory resume based on high estimates for the number of neurons in its forebrain."

"This conclusion emerged from a paradigm whereby neurological variables estimated from endocasts can, so it is claimed, be used to infer metabolic parameters, behaviors, and longevity in fossil species."

In their new study, Dr. George and co-authors took a closer look at techniques used to predict both brain size and neuron numbers in dinosaur brains.

They found that previous assumptions about brain size in dinosaurs, and the number of neurons their brains contained, were unreliable.

This new research follows decades of analysis in which paleontologists and biologists have examined dinosaur brain size and anatomy, and used these data to infer behavior and lifestyle.

Information on dinosaur brains comes from mineral infillings of the brain cavity, termed endocasts, as well as the shapes of the cavities themselves.

The authors found that their brain size had been overestimated — especially that of the forebrain — and thus neuron counts as well.

In addition, they show that neuron count estimates are not a reliable guide to intelligence.

"To reliably reconstruct the biology of long-extinct species, researchers should look at multiple lines of evidence, including skeletal anatomy, bone histology, the behavior of living relatives, and trace fossils," they said.

"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," Dr. Hady added.

"We argue that it's not good practice to predict intelligence in extinct species when neuron counts reconstructed from endocasts are all we have to go on," said Dr. Kai Caspar, a paleontologist at the Heinrich Heine University.

"Neuron counts are not good predictors of cognitive performance, and using them to predict intelligence in long-extinct species can lead to highly misleading interpretations," said Dr. Ornella Bertrand, a paleontologist at the Institut Català de Paleontologia Miquel Crusafont.

"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," said Dr. Darren Naish, a paleontologist at the University of Southampton.

"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 results were published in The Anatomical Record.

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Kai R. Caspar et al. How smart was T. rex? Testing claims of exceptional cognition in dinosaurs and the application of neuron count estimates in palaeontological research. The Anatomical Record, published online April 26, 2024; doi: 10.1002/ar.25459