Gary Larson framed the issue best in a famous Far Side cartoon. A Stegosaurus behind a podium addresses an audience of his fellow dinosaurs: "The picture's pretty bleak, gentlemen… the world's climates are changing, the mammals are taking over, and we all have a brain about the size of a walnut." (See a slideshow of the 10 smartest dinosaurs.)
For over a century, that quote has pretty much summed up popular (and even professional) opinions about dinosaur intelligence. It didn't help that one of the earliest dinosaurs to be discovered and classified (the above-named Stegosaurus, in 1877) possessed an unusually small brain, about the size of, yes, a walnut (its brain was so small, in fact, that paleontologists once speculated that Stegosaurus had a supplementary brain in its butt). It also didn't help that dinosaurs are long extinct; wiped out by the famine and freezing temperatures in the wake of the K/T Extinction 65 million years ago. If only they'd been smarter, we like to think, some of them might have found a way to survive!
One Measure of Dinosaur Intelligence: EQ
Since there's no way to travel back in time and give an Iguanodon an IQ test, naturalists have developed an indirect means of evaluating the intelligence of extinct (as well as living) animals. The Encephalization Quotient, or EQ, measures the size of a creature's brain against the size of the rest of its body, and compares this ratio to that of other species of roughly the same size.
Part of what makes us human beings smart is the enormous size of our brains compared to our bodies; our EQ measures a hefty 5. That may not seem like such a big number, so let's look at the EQs of some other mammals: on this scale, wildebeests weigh in at .68, African elephants at .63, and opossums at .39. As you might expect, monkeys have higher EQs: 1.5 for a red colobus, 2.5 for a capuchin. Dolphins are the only animals on the planet with EQs even close to those of humans; the bottlenose comes in at 3.6. (By the way, EQ scales vary considerably; some authorities set the average human EQ at about 8, with the EQ of other creatures scaled up proportionally.)
As you might expect, the EQs of dinosaurs (based on the analysis of their fossil remains) are spread across the lower end of the spectrum. Triceratops weighs in at a scant .11 on the EQ scale, and it was the class valedictorian compared to lumbering sauropods like Brachiosaurus, which don't even come close to hitting the .1 mark. However, some of the swift, two-legged, feathered dinosaurs of the Mesozoic Era posted relatively high EQ scores-not quite as smart as modern wildebeests, but not that much dumber, either.
How Smart Were Carnivorous Dinosaurs?
One of the trickiest aspects of animal intelligence is that, as a rule, a creature only has to be smart enough to prosper in its given ecosystem and avoid being eaten. Since plant-eating sauropods and titanosaurs were so massively dumb, the predators that fed on them only needed to be marginally smarter-and most of the relative increase in the brain size of these carnivores can be attributed to their need for better smell, vision and muscular coordination, their tools for the hunt. (For that matter, one can argue that the reason sauropods were so dumb is because they only had to be marginally smarter than the giant ferns they munched on!)
However, it's possible to swing the pendulum too far in the other direction and exaggerate the intelligence of carnivorous dinosaurs. For example, the doorknob-turning, pack-hunting Velociraptors of Jurassic Park and Jurassic World are a complete fantasy-if you met a live Velociraptor today, it would probably strike you as slightly dumber (though a lot more dangerous) than a chicken. You certainly wouldn't be able to teach it tricks, since its EQ would be an order of magnitude below that of a dog or cat. (This is part of the reason why dinosaurs, as a general rule, don't make very good pets.)
Could Dinosaurs Have Evolved Intelligence?
It's easy, from our present-day perspective, to poke fun at the walnut-brained dinosaurs that lived tens of millions of years ago. However, you should bear in mind that the proto-humans of five or six million years ago weren't exactly Einsteins, either-even though, as stated above, they were significantly smarter than the other mammals in their savannah ecosystems. In other words, if you managed to time-transport a five-year-old Neanderthal into the present day, she probably wouldn't do very well in kindergarten!
This raises the question: what if at least some dinosaurs had survived the K/T Extinction 65 million years ago? Dale Russell, the one-time curator of vertebrate fossils at the National Museum of Canada, once caused a stir with his speculation that Troodon -a human-sized theropod dinosaur about as smart as an opossum-might eventually have evolved a human-sized level of intelligence if it had been left to evolve for another few million years. It should be noted, however, that Russell didn't propose this as a serious theory, which will come as a disappointment to those who still believe intelligent "reptoids" live among us.