Stegosaurus is the namesake for a large family of dinosaurs whose members were found all over the world. The Stegosaurus was a peaceful herbivore, and probably roamed the prehistoric highlands in herds that size from small to large numbers, grazing on low ground plants. It had a very low intelligence (its brain was the size of a walnut). The bony plates on its back may have served a dual purpose of a body temperature regulation, and protection from large flesh-eating predators. Different species had different numbers of tail spikes. Stegosaurus had 4 spikes on its tail.
Stegosaurus lived during the Late Jurassic Period over 150 million years ago in Western North America. It shared the environments with the massive sauropod dinosaurs, Dryosaurus, and of course Allosaurus and Ceratosaurus.
Stegosaurus stood 14 feet tall (17 at tallest plate), measured up to about 10-12 meters (30-36 ft) in length and weighed 3-7 tons (6,000-14,000 lbs). It had much shorter limbs in front than in back, so its back--which was lined with large bony triangular plates--appeared arched from the neck to the hip. Instead of claws, its hands and feet had evolved into broad, blunt-hoofed feet.
Most fascinating to people are the distinctive row of 17 bony, knife-shaped plates arranged in a double row along its curved back. There has been a great deal of debate about their use and arrangement. The plates ranged in heights, varying from 4 inches up to almost 3 feet tall and 2 feet wide (.6 m) and gave Stegosaurus its unique appearance. The most prevalent theory is that they were used for cooling or heating the animal. A more recent theory, however, suggests that they could have been used as a display during courtship and that they may have been brightly colored. It is also possible that they could move up and down, perhaps to intimidate predators.
The spikes on its tail are also the subjects of some controversy. For years every model of Stegosaurus showed it with the spikes sticking up into the air. It is only since the 1990s that it has become accepted that these spikes stuck out horizontal to the ground, which would have been a potent defensive weapon when swung at a hunter. The two pairs of long lethal spikes extending horizontally near the end of the tail. Pointing up to 3-4 feet long, those spikes are as long as baseball bats. Stegosaurus is often called the dumbest dinosaur because of its incredibly small brain. In fact, most scientists believe that its brain was too small to control such a large creature and that it used an auxiliary "brain" located above its rear legs to help control its movements. This was not actually a brain, but a bundle of nerves that helped relay information from its real brain. Its brain was once thought to have been the size of a walnut, but CAT-scans proved that it was actually the size of 5 walnuts.
Stegosaurus would have lived in family groups and herds, moving slowly through forests while eating the low-growing plants.
Of all members of the Stegosaur family, Setgosaurus was the only one found in North America.