Stegosaurus
Mary Evans Picture Library/Deagostini Editore
Stegosaurus was a plant-eating dinosaur that had plates running along its back and long spikes on its tail. It was between 26-30 feet long, and weighed about 6,800 pounds, but its brain was the size of a walnut. It lived during the late Jurassic Period, approximately 156 to140 million years ago.