Dianna Boyer

Stegosaurus had a brain the size of a walnut—about 3 inches (8 cm) long and weighing just 2.8 ounces (80 grams)—despite its body being the size of a bus? This made its brain-to-body ratio one of the smallest among dinosaurs, leading some to joke it had a "second brain" in its hips (actually a bundle of nerves called the sacral ganglion, which helped control its hind legs and tail).