Stegosaurus was a herbivore (plant-eater) that lived in North America and Europe (the first European specimen was found in Portugal in 2006) during the late Jurassic period, about 155 to 144 million years ago. The creature's name, which was chosen by Othniel C. Marsh in 1877, means "roof lizard".
Stegosaurus was up to 30 feet (9.1 meters) long. An average Stegosaurus was around 20 feet (6.1 meters) long, and weighed 2 tons. Stegosaurus had much longer hind legs than forelegs, and very strong muscles around its hips. So, although Stegosaurus walked on all fours, it is thought likely that the animal could have lifted its forelegs off the ground to eat from the branches of trees.
Stegosaurus bony plates on its back that could have been used for protection, and possibly temperature regulation. The largest of the plates were over 2 feet (60 centimeters) high. Nobody is absolutely sure how the plates on the back were arranged, because the plates have never been found still attached to the skeleton. Some scientist believe the plates may have lay flat on the skin. However, most scientists believe the plates stood erect on the back, and were arranged in pairs or a zigzag pattern. Stegosaurus also had pairs of spikes on its tail which were about 3 feet (0.9 meters) long. There were several species of Stegosaurus, and the number of tail spikes varied between Stegosaurus species.