Stegosaurus is one of the most famous of the great dinosaurs. It lived during the late Jurassic period, about 156 to 140 million years ago. It grew to be about 26 to 30 feet long and about nine feet tall. It weighed about 6,800 pounds. It was about the size of a bus. Stegosaurus is known for the big plates running down its back and tail. Its name means “covered lizard”. It had 17 bony plates that grew right out of its back. Stegosaurus also had spikes at the end of its flexible tail. These were about four feet long. Stegosaurus could have used its plates and spikes as protection against large meat-eating predators. It was so heavy that it couldn’t run away very quickly when a carnivore attacked.
No one knows exactly how these plates were used. Some paleontologists believe that if the plates had blood vessels running through them, then they could probably change color. This would have looked very impressive to a mate or very scary to a predator! And if the plates had blood vessels, then Stegosaurus could also use them to keep warm in the winter and cool in the summer. If a Stegosaur stood with its plates facing the sun, its blood would heat up and pump back into the creature’s body. When it needed to cool down, it could stand in a shady place and let the blood in its plates cool off. Its back legs were longer and thicker than its front legs, so its head stayed low to the ground. The front legs had five toes with short, hoof-like claws. The back feet had three short, wide toes with hooves. Its head was long and narrow.
Stegosaurus had a tiny brain for its body size. The brain was only about the size of a walnut. We know this by studying the space in its skull. This dinosaur might have had a second brain at the back of its body to help pass messages along. This bundle of nerves, which might have been larger than its other brain, may have controlled the animal's hind legs and tail. Stegosaurus was an herbivore, meaning that it only ate plants. It didn’t have any front teeth, but a hard beak at the front of its mouth. It used this beak to snip down tough plants. It chewed with its back teeth and could store food in its cheeks. It was a very successful dinosaur, meaning that it was found in many different parts of the earth. The first Stegosaurus fossil was found in Colorado, North America in 1876. Many fossils of Stegosaurus have been found in Utah, Wyoming and Colorado, North America. They have also been found in western Europe, southern India, China, and southern Africa.