It is interesting to compare the brain of a very large dinosaur with the brain of an equally large modern mammal like the whale. The largest dinosaurs weighed as much as 100 tons. Whales also weigh as much as 100 tons and are, as the dinosaurs were in their time, the largest animals alive today. The brain of a large whale is a huge mass of gray matter, nearly a foot and a half across, that weighs about 20 pounds. The possessor of this mammoth brain is an intelligent animal. Some whales have a remarkable memory’ capacity; they can memorize a complex whale song that goes on
for hours, and repeat it note for note a year later. The brains of the largest dinosaurs, on the other hand, such as Supersaurus, were only the size of an orange, and weighed about half a pound. Yet, that small amount of gray matter had to exercise control over the same 100-ton bulk that is commanded by the 20-pound brain of the largest whales.
Scientists who specialize in the study of brains and intelligence have plotted charts of brain weight against body weight for many kinds of animals. They find that when the ratio of brain weight to body weight is as small as it was in the Supersaurus, the behavior of the animal is stereotyped, automatic, and unintelligent. The reason is clear: a large body has many large muscles and needs many nerve fibers for its coordination. When that large body is controlled by a small brain, every neuron in this brain must be used to move the body through its basic survival routines: find food! flee from the predator! and so on.

The Supersaurus was not an unusually stupid dinosaur, and dinosaurs were not unusually stupid reptiles. In fact, dinosaurs had normal intelligence for reptiles. Of course, there was a spread in braininess among the dinosaurs. But the same is true among modem mammals; plant-eaters like the cow are among the least intelligent mammals, while alert carnivores like the wolf are among the most intelligent. However, the dinosaurs as a group were generally less intelligent than the early mammals as a group. This held then, and still holds today, all the way up and down the scale of sizes. A little lizard, for example, has a considerably smaller brain than a chipmunk of the same size and displays a far less flexible repertoire.