Few people know much about Stegosaurus beyond the fact that a) it looked funny and b) it was dumber than the average dinosaur. Here are 10 facts about this popular plant-eater with the spiked tail and plated back. (See also a gallery of Stegosaurus pictures.)
1. Stegosaurus had a brain the size of a walnut.
The four-ton Stegosaurus was equipped with an unusually small brain, only about the size of a modern dog's. It was once proposed (by no less an eminence than the famous paleontologist Othniel C. Marsh) that this none-too-bright herbivore had supplementary grey matter located in its hip region, but scientists quickly soured on this "brain in the butt" theory.
2. No one knows why Stegosaurus had plates...
Did Stegosaurus evolve its thin, tough, roughly triangular plates as a form of defense against larger predators? Were they a sexually selected characteristic, meaning males with bigger plates had a better chance of mating with females? Or could they have been used to regulate this dinosaur's body temperature? For answers to these and other questions, see Why Did Stegosaurus Have Plates on its Back?
3. ...or exactly how these plates were arranged along its back.
The name Stegosaurus means "roofed lizard," reflecting the belief of 19th-century paleontologists that this dinosaur's plates lay flat along its back, like a form of armor. Various reconstructions have been offered since then, the most convincing of which has the plates alternating in parallel rows (and facing pointy side up) from this dinosaur's neck all the way down to its butt.
4. Stegosaurus' spiked tail is called a "thagomizer."
Way back in 1982, a famous Far Side cartoon showed a group of cavemen clustered around a picture of a Stegosaurus' tail; one of them points to the sharp spikes and says, "Now this end is called the thagomizer...after the late Thag Simmons." The word "thagomizer" has been used by paleontologists ever since. (See Allosaurus vs. Stegosaurus - Who Wins? for an analysis of how effective this thagomizer would have been in actual combat.)
5. Most stegosaurs hailed from Asia, not North America.
Although it's by far the most famous, Stegosaurus wasn't the only spiked, plated dinosaur of the Jurassic period. Remains of these odd-looking reptiles have been found all over the world, with the largest concentration in Asia--hence the odd-sounding stegosaur genera Chialingosaurus, Chungkingosaurus and Tuojiangosaurus.
6. It was once thought that Stegosaurus walked on two legs.
Because it was discovered such a long time ago, Stegosaurus is the poster-lizard for wacky dinosaur theories (such as that brain-in-the-butt blunder, detailed above). Paleontologists once thought this plant-eater was bipedal, like Tyrannosaurus Rex; even today, some experts argue that Stegosaurus may have been occasionally capable of rearing back on its two hind feet, though few people are convinced.
7. Stegosaurus supplemented its diet with rocks.
Like many herbivorous dinosaurs, Stegosaurus swallowed small rocks (known as gastroliths) that helped mash up the tough vegetable matter in its enormous stomach, of which it would have had to eat hundreds of pounds a day. Of course, it's also possible that Stegosaurus swallowed rocks because it had a brain the size of walnut; who knows?
8. Stegosaurus is the state dinosaur of Colorado.
Back in 1982 (around the same time Gary Larson was coining the word "thagomizer"), the governor of Colorado signed a bill making Stegosaurus the official state dinosaur, after a two-year write-in campaign by thousands of fourth-grade students. This is a major honor, considering the huge number of dinosaurs that have been discovered in Colorado, including Allosaurus, Apatosaurus and Ornithomimus.
9. Unlike most of its contemporaries, Stegosaurus had cheeks.
Although it undoubtedly had a tiny brain, Stegosaurus did sport one relatively advanced feature: based on an analysis of its teeth, experts believe this plant-eater may have possessed cheeks. Why were cheeks so important? Well, they gave Stegosaurus leeway to thoroughly chew and pre-digest its food, and also allowed it to store more vegetable matter than non-cheeked dinosaurs.
10. Stegosaurus was closely related to Ankylosaurus.
Back in the Mesozoic Era, the Jurassic stegosaurs (plated, spiked dinosaurs) were first cousins of the Cretaceous ankylosaurs (armored dinosaurs), both of these families grouped under the larger classification of "thyreophorans" (Greek for "shield bearers). Like Stegosaurus, Ankylosaurus was a low-slung, four-footed plant-eater, and even less appetizing in the eyes of ravenous raptors.