We knew that they were perfectly adapted to their world, that they dominated the planet by land, sea and air, that many cared for their young, that some hunted in groups and that, as a whole, dinosaurs already showed, before they became extinct more than 60 years ago. millions of years ago, many of the behaviors that today ensure the survival of the animals that succeeded them. Something special, of course, these creatures had to have to be the absolute masters of the world for over a hundred million years…
But biologist and neuroanatomist Suzana Herculano-Houzel of Vanderbilt University in Tennessee has gone much further, suggesting in a controversial study that at least some dinosaurs had the same or even more neurons than modern primates.
Which would imply that they were highly intelligent, far more intelligent than anyone has ever thought, and intelligent enough to use tools, something only humans and a select handful of other living animals are capable of.
The article, published just a few days ago in the ‘Journal of Comparative Neurology’, has caused a sensation in the scientific community, especially among paleontologists.
Comments on social networks, both for and against, are multiplying, and the old controversy over ‘animal intelligence’ takes on a new dimension by now being projected into the remote past of life on Earth. Were dinosaurs intelligent or not? That is the question.
measure intelligence
Of course, measuring the degree of intelligence of dinosaurs, or of any other extinct creature whose behavior we cannot directly observe, is not an easy task. To do this, scientists have used for decades an indicator called ‘encephalization quotient’ (EQ), which is obtained by calculating the relationship between the size and the body of the animal. For example, a T. Rex, one of the largest carnivorous dinosaurs that ever lived, had an EQ of about 2.4, while a German Shepherd Dog has it of 3.1 and a human of 7.8. According to this, the fearsome Tyrannosaurus was dumber than a dog and, of course, much more than a person.
But the EQ can be misleading, since in many animals the size of the body and the size of the brain evolve independently, so using this parameter to measure intelligence can lead to gross errors. In search of a more reliable alternative, Suzana Herculano-Houzel decided to measure completely differently: the density of neurons in the cerebral cortexthe outer area of the brain, critical to the performance of most intelligence-related tasks. The method, which involves dissolving the brains in a detergent solution and then counting the neurons in the resulting ‘soup’, had already been used to estimate the number of neurons in many animal species, including humans. The downside is that this obviously cannot be done with dinosaur brains, which do not withstand the passage of tens of millions of years and therefore never reach the hands of scientists.
an indirect method
Fortunately, and despite their virtual disappearance after the fall of a large meteorite 66 million years ago, the dinosaurs did not completely disappear. In fact, the group of theropods, to which carnivores such as the famous velociraptors and T. Rex itself belonged, is related to today’s birds, which are their direct descendants. So when a large database was published a year ago showing that compared to reptiles, birds (and mammals) have much higher densities of neurons in their cortices, Herculano-Houzel saw his opportunity: thanks. to birds, he could estimate the neuronal density of dinosaurs. If not all, at least theropods.
To do this, the researcher used last year’s database and mixed it with estimates of dinosaur brain mass obtained over the years with CT scans of their skulls. With this data combined, she developed an equation that relates an animal’s brain mass to its approximate number of neurons. And he found that, unsurprisingly, theropod brains follow roughly the same rules as modern warm-blooded birds like ostriches, while the brains of sauropod dinosaurs like Brachiosaurus are more similar to those of modern cold-blooded reptiles.
By crunching the numbers and applying them to specific species, Herculano-Houzel found, for example, that Alioramus, a 20-foot-long theropod that lived about 70 million years ago in what is now Mongolia, was just over billion neurons in its cortex, similar to capuchin monkeys. And that T. Rex, with a brain that weighed just over 300 g, had approximately 3.3 billion cortical neurons, a density higher than that of living baboons.
These results, the researcher says, have made her feel “a completely new respect for the Tyrannosaurus rex. Something that big, with those teeth, and with the cognitive ability of a baboon…it’s truly terrifying.”
For and against
The study, of course, has elicited all kinds of reactions. Some, like Fabien Knoll, from the Dinópolis Foundation, in Teruel, are happy to finally have “an idea of the possible number of neurons that dinosaurs could have”, although he qualifies that “we would need more data from the fossil record.” Others, like Stig Walsh, Senior Curator of Vertebrate Paleobiology at the National Museums of Scotland, believe it is “a bunch of conclusions or suggestions based on what is essentially a single extrapolation.”
Amy Balanoff, for her part, an evolutionary biologist at Johns Hopkins University, points out that a good part of the data behind the estimates of brain mass made by Herculano-Houzel, are out of date, since they are from 2013, when she herself , (Amy Balanoff) published a new updated database in 2020 that provided new data.
Despite these doubts, the study has been generally well received, as it opens the door to a better understanding of the mental acuity of these incredible creatures.