The Tyrannosaurus Rex has always gotten a bad rap. It is portrayed as a bully in the blockbuster film Jurassic Park, people joke about its short arms, and many assume it had a pea-sized brain inside its head.
It turns out that sauropods should be the butt of our jokes, at least the ones about brain size. Sauropods, as I learned at the American Museum of Natural History’s “World’s Largest Dinosaurs” exhibit, had tiny brains even relative to other dinosaurs. These giant dinosaurs (for the less nerdy readers, sauropods include brachiosaurus and other “really long-necked” dinos) had a gland responsible for secreting hormones relating to growth that made up as much as 10 percent of their brain volume. The gland certainly did its job, but it helps explain why the overall brain size wasn’t much larger than a dog’s brain, despite its massive body.
Sauropods, like stegosaurus and many other species, were herbivores. Simply put, they didn’t have to be very smart because their food wasn’t trying to escape (although greater intelligence probably would have helped them avoid becoming another dinosaur’s food). T. Rex, on the other hand, was a hunter. While research suggests it was not intelligent by any means—its powerful jaws were its greatest asset and took up a lot of head room—it did have a large olfactory lobe and a well developed inner ear. In other words, T. Rex’s sense of smell and hearing were probably strong.
Even so, large dinosaurs likely only had several billion neurons in their brains, while humans have 100 billion. Our minds are obviously capable of much higher levels of thought, but given what many carnivores like T. Rex had to compute while chasing prey, they needed more powerful brains than the sauropods. Now if you want to talk about arm size…