The Stegosaurus was a dinosaur that lived about 156 to 140 million years ago, in the Jurassic Period; when the climate was warm and moist with high sea levels. During the Jurassic Period, large areas were flooded, and there were forests (both temperate and subtropical), as well as coral reefs. The extensive amounts of water during the Jurassic Period helped moderate the seasonality.
The Stegosaurus was an ornithischian dinosaur and was a part of the group Thyreophora and the family Stegosauridae.
Fossils of Stegosaurus have mainly been found in western North America, but have also been found in Western Europe, southern India, China and southern Africa. The very first Stegosaurus fossil was discovered in the United States, in Colorado, by M. P. Felch in 1876. However, Stegosaurus did not get its name until a year later, in 1877. It was named by paleontologist Othniel C. Marsh. Also discovered in Colorado was the most complete Stegosaurus that has yet to be found. Nicknamed "Spike," this Stegosaurus was discovered near Canon City, Colorado, in 1992 by Bryan Small, Tim Seeber and Kenneth Carpenter.
The Stegosaurus was a plant eater, or an herbivore. It would have to have eaten large amounts of plant material every day in order to maintain its considerable size. It is believed that the Stegosaurus would have had few competitors, as it preferred food that was near the ground.
The Stegosaurus was 26 to 30 feet long (8 to 9 m), about 9 feet tall (2.75 m) and weighed about 6,800 pounds (3,100 kg).
The Stegosaurus is named for the plates that ran along its back. Stegosaurus means “roofed lizard,” or “covered lizard.” Nineteenth-century paleontologists believed the plates lay flat along its back, instead of sticking straight up. These plates were large, flat, bony and triangular. There were 17 in total and they ran in two rows along the back and tail of the Stegosaurus. It is still not known what purpose these plates held. They were made of bone filled with tube-like tunnels. The largest plate would have been about 2.5 feet (76 centimeters) tall and just as long. It is thought that since the plates were more than likely well-nourished by blood vessels, they may have been used to regulate the Stegosaurus’ temperature. Other possible uses of the plates are thought to be protection and mating display purposes.
Another distinctive physical feature of the Stegosaurus was the heavy, spiked tail. This would have been used for protection. The spikes were called thagomizers; the name of which came from a Gary Larson “Far Side” cartoon in which a caveman explains that the end of a Stegosaurus’ tail is called a thagomizer, named for the late Thag Simmons. The spikes could be up to four feet long and pointed to the sides of the tail. Different species of Stegosaurus could have different numbers of tail spikes.
The Stegosaurus had even more protection in the way of armor-like scutes on its neck, the pelvic area and, in some species, on the sides.
Its very small brain, the size of a walnut (weighing about 2.5 to 2.9 ounces , or 70 to 80 grams), was contained within a very small head carried close to the ground. The skull of the Stegosaurus was long, pointed and narrow. It had a toothless beak and small cheek teeth, with grooves for crushing its food.
The Stegosaurus was quadrupedal, meaning that it walked on four legs. Its back legs were twice as long as its front legs. The forefeet had five short, wide toes that had short, hoof-like tips. The rear feet had three, instead of five, short, wide toes.
There was a minor mass extinction near the end of the Jurassic Period, during which most of the Stegosaurs were wiped out.