Real Stegosaurus were plant-eating dinosaurs that were the largest and most famous members of the stegosaur family, at about 9 metres long. It lived during the Jurassic period, from 155 to 150 million years ago. Its most distinctive features are the row of plates along its back and the double row of spikes on its tail. This tail weapon is sometimes called the thagomizer, in honour of a Far Side cartoon by Gary Larson which humourously (as, of course, dinosaurs lived much earlier than ancient humans) depicted a group of cavemen warning of the danger of a stegosaur's tail. Fossils of meat-eating dinosaurs have been found with punctures in their bones from a stegosaur's tail spikes.Stegosaurus is also notorious for having a brain the size of a walnut, although this seems to have been false - its brain was about twice that size, and Stegosaurus did not need the help of a "second brain" in the hip, which is now thought to have stored energy. Stegosaurus had armour under its throat, necessary protection for an animal living at the same time as predators like Allosaurus. The plates were used to help warm the animal's body or as a threat display against its enemies. While Stegosaurus could not walk on two feet, it may have been able to rear up on its hindlegs using its tail as a prop, as Teggs sometimes does in the books. Its name means "roofed lizard".