How smart were T-Rex? Study that suggested dinosaurs were as intelligent as monkeys called into question

Published in 2023 in the scientific journal Journal of Comparative Neurology, a study led by neuroscientist Suzana Herculano-Houzel, concluded that the brains of theropod dinosaurs – a species of which T-Rex are part – would have similarities to those of monkeys and baboons. In her conclusions, the author stated that these dinosaurs had a high number of neurons, similar to the primate brain, and were substantially more intelligent than science thought.

However, a recent scientific review published in the scientific journal The Anatomical Record concluded that Herculano-Houzel’s study overestimated the size of the dinosaur brain, as well as the neuron count. “Furthermore, neuron count estimates were not a reliable indicator for inferring intelligence,” explained Hady George, one of the researchers at the University of Bristol, in the United Kingdom.

The international team of paleontologists, behavioral scientists and neurologists re-examined the size and structure of the dinosaurs’ brains and concluded that they bear more similarities to reptile species, such as crocodiles and lizards, than to primate species. “The possibility that the T-Rex was as intelligent as a baboon is fascinating and terrifying, but our study shows how all the data we have contradicts this idea. They were more like giant intelligent crocodiles, which is equally fascinating,” concluded Darren Naish, a researcher at the University of Southampton.

Currently, studies on the brain of dinosaurs are based on the observation of internal molds of the braincase, as well as the shapes of the skulls of fossil dinosaurs, resources that serve to build a more faithful image of the brains of these living beings before they were extinct. “The best way to determine the intelligence of dinosaurs and other extinct animals is to use many lines of evidence, from gross anatomy to fossil footprints, rather than relying solely on estimates of the number of neurons,” George continued.

To reconstruct the biological traits of dinosaurs, the researchers involved in the scientific review considered that factors such as skeletal anatomy, bone histology, the behavior of living relatives and existing fossil remains must be observed. “Neuron counts are not a good indicator of cognitive performance and their use to predict intelligence in long-extinct species can lead to very misleading interpretations”, believes Ornella Bertrand, one of the authors involved in the study.