General
Stegosaurus literally means "Covered Lizard" and they lived in the late Jurassic period about 156-140 million years ago. With the bony plates down its back and spikes at the end of the tail, Stegosaurus is one of the more bizarre and best known dinosaurs. Stegosaurus was a bird-hipped (ornithischian) plant eating (herbivore) dinosaur. Stegosaurus was the largest and one of the last of the Stegosauridae, which also includes Kentrosaurus and Tuojiangosaurus. It is not known if Stegosaurus was a herding animal.

Fossils
Many fossils have been found in western North America (Utah, Colorado and Wyoming), but also in western Europe, southern India, China, and southern Africa. The first fossil was found in 1876 and named by O.C. Marsh. 

Anatomy
Stegosaurus was 20-30 feet (6-9 m) long, 8-9.5 feet (2.4-2.8 m) tall at the hips, and weighed 2-3 tons. Its head was long and narrow, it had a toothless beak and small cheek teeth. The head was carried about 3 feet (1 m) from the ground. It is generally thought that Stegosaurus walked on all four legs, but it is not known if it could raise up on the back legs to eat.

Back plates
Stegosaurus had 17 bony plates embedded along its back. It is still debated if they were upright, and even the function is uncertain. The plates was not solid and could have contained a network of blood vessels. It is widely believed that Stegosaurus was cold-blooded and used the plates to regulate the body temperature. But they may have also been used for protection or mating display purposes. 

Spiked tail
Stegosaurus had spikes at the end of its flexible tail. The spikes were up to four feet long, enough to provide a serious defense against predators such as the Allosaurus. The number of spikes varied from 4 to 8 at the different species.

Small Brain
Stegosaurus had a low intelligence as its small brain was only the size of a walnut. But it had an enlargement in the spinal cord in the hip area. This nerve relay station was twenty times larger than its brain and was probably used to control its massive hind legs and tail.