Researching intelligence is an extremely difficult task, even in animals alive today. In part that’s because much of the scientific jury is still out on what intelligence even is.
So, estimating the smarts of any creature that is now extinct is an especially tall order. In the case of dinosaurs, combine the fact that they have been gone for tens of millions of years, and this task requires … even more brains, and speculation.
Nevertheless, scholars have pursued several different methods to tackle the question of dino intelligence.
Their approaches rely on a mix of morphological proxies of intelligence like absolute and relative brain size and neuron count, or mapping dinosaurs against their relatives in the evolutionary tree.
As an added challenge, the term dinosaur itself is a broad category. These creatures spanned great diversity in their morphology, lifestyles and diets, which means that some dinosaurs were likely much smarter than others.
Suffice it to say, the debate is rife, and the research methods are mind-boggling.
How Smart Were Dinosaurs?
In the 1970s, when scientists first questioned whether there was information to glean about dino smarts from morphological traits — like how big a brain is — they developed the EQ, aka encephalization quotient.
This calculation measures the weight of an animal’s brain compared to the size of the rest of the body, then contrasts that figure with other animals within its taxonomic group.
Humans, with their massive brains compared to their relatively small bodies, have an EQ of approximately 7.5.
Dolphins are somewhere between 4.0 and 4.5. And chimps land between 2.2 and 2.5.
Measuring the Size of a Dinosaur Brain
As for the dino family, the Tyrannosaurus rex falls between 2.0 and 2.4, when compared to other reptiles.
Presumably, that means T. rex might have been as bright as chimps, according to the book The Rise and Fall of the Dinosaurs by paleontologist Steve Brusatte.
This would seem to suggest that T. rex wasn’t dumb at all.
Read More: Tyrannosaurus Rex: Scary. Smart. Social?
Encephalization Quotient Methods
But while the encephalization quotient was a great starting tool for scientists over the past decades, there are tensions among scholars regarding how much it can actually be trusted.
“These animals were incredibly large, so you get a rather skewed idea, I think, of the importance of the brain size to the animal,” says Scott Rogers, professor of neurobiology at the University of Utah, who also uses brain morphology to learn more about the behavior of dinosaurs.
One important consideration is that Brusatte’s calculation for the T. rex brain is based on comparing it to modern reptiles, resulting in a high EQ number. If, instead, you compare it to birds, it’s actually exceptionally low, at 0.1-0.2, according to a 2013 study.
Thus, EQ comparisons across major groups of animals might not be that meaningful.
Reconsidering Brain Mass
On the other hand, brain mass is notoriously quite tricky to calculate.
The Brusatte calculations assume that 50 percent of the brain cavity in an adult T. rex was filled by the brain. But modern crocodiles only fill 30 percent of their headspace.
Plus, when tested on living animals today, brain size doesn’t match their cognitive abilities particularly well.
So, comparing T. rex smarts to chimp smarts would be highly misleading.
Were Dinosaurs Intelligent?
In January of this year, a research paper in Journal of Comparative Neurology argued that some dinos were much smarter than previously thought.
Tyrannosauruses and velociraptors could be dubbed “primates of their time,” Suzana Herculano-Houzel, a neuroscientist at Vanderbilt University who authored the study told the Washington Post.
This was based in part on findings that they had approximately 3 billion cerebral neurons in a brain weighing 343 grams, more than baboons.
This would mean T. rex was nothing like the idiot we’ve long thought it was.
Yet, Kai Robert Caspar, a researcher of comparative cognition from Heinrich-Heine University Düsseldorf, and many of his colleagues have questioned these results. They’re working on a research paper to debunk these findings.
Challenging the Neuron Theory
Firstly, Caspar says, there are errors in the paper’s methods: Once again, it assumes T. rex’s brain filled the whole cranial cavity. It also assumes a neuron density similar to that of some birds, which is not necessarily the case in the brain of the T. rex.
Secondly, just like EQ, it might be inaccurate to make assumptions about smarts based on quantity, not quality.
“I'm quite skeptical of whether we should accept neuron counts as a good proxy of cognitive ability,” says Caspar. “The neuron might be the computational unit of the nervous system … it also matters how neurons are connected to each other and organized.”
Considering Living Relatives of Dinosaurs
Let's not forget that some animals alive today are distant relatives of the dinosaurs.
These include birds, which evolved from the carnivorous dinosaurs called theropods (and included T. rex ), and crocodiles, which evolved from an ancestor of dinosaurs, the archosaurs (aka ruling reptiles), also related to T. rex.
On the evolutionary tree, these animals sit on both sides of the dinosaurs, so scholars can draw comparisons and make educated guesses about what kind of characteristics and traits from these creatures today were also present in dinosaurs back then.
This technique is called phylogenetic bracketing.
“If you have a certain cognitive trait, if it would be present both in crocodilians and across birds, then I think we could make an argument that this was also present in dinosaurs,” says Caspar.
Compared to Birds and Crocodiles
According to this theory, scholars have posited that some dinosaurs were probably as smart as birds and others were as smart as crocs.
But phylogenetic bracketing does not allow you to predict stuff like this, says Caspar, because you need to take other lines of evidence into account.
For example, the brain morphology of T. rex is more similar to crocodiles than to birds, despite being more closely related to the latter. And that factor is much more telling than estimating a trait based on its presence or absence in living relatives.
Sizing Up Brain Casts
Rogers at the University of Utah specializes in using the internal measurements from the skull of dinosaurs — aka ‘endocasts’ — and comparing them to brain models of their living relatives.
For instance, when taking the cast of an allosaurus brain (quite similar to the T. rex ) and placing it next to the model of what an alligator brain looks like, it’s clear they are very similar shapes.
“Bingo,” says Rogers, holding the two next to each other. “Super good match.”
This, he says, is the most accurate “very first evidence” of what behavior an allosaurus or T. rex exhibited and how their brains worked. That’s because the method can reveal where the neurons were concentrated, and compare that to the function of different brain areas in animals alive today.
Neuron Patterns Like Crocodiles
“[Like crocodiles,] the neurons were concentrated down here in the sensory section, in the olfactory part. Not so much up in here where you'd expect the telencephalon to be,” Rogers says.
The latter region is much more developed in birds and mammals, and responsible for sensory processing and learning.
That now means we can make estimated guesses that the T. rex was possibly clever in the same way that crocodiles and alligators are.
“That's the kind of comparison I think is useful,” Rogers says. “Can we say it’s exact? Well, of course not.”
The Ultimate Intelligence Test
Moving forward, it’s imperative that scholars use an “integrative approach,” according to Caspar.
This means relying on as many different lines of evidence as possible, from neuron count to endocasts to making comparisons with living animals.
Ultimately we just really do not know how smart dinosaurs could have been, according to Caspar.
Rogers adds that looking at the context might provide some answers: “Intelligence really is more of an idea of adaptiveness. I mean, how successful are you in your environment?”
From his perspective, dinosaurs were around for tens of millions of years and did “extremely well.”
“It took a rather substantial change in the environment to wipe them out,” he says. “For me, that sort of suggests they were actually quite intelligent.”
Read More: What Killed the Dinosaurs?