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Stegosaurus was a dinosaur that lived during the Jurassic period, between about 155 and 144 million years ago. It was a herbivore (plant eater) that lived in the regions that are today North America and Europe (a Stegosaurus fossil was found in Portugal in 2006).

Stegosaurus is quite simple to recognize. It had a small head, a bulky body, and a tail. Stegosaurus is usually depicted as a quadraped (walking on four legs), but it probably could have stood in a bipedal stance on its powerful hind legs when browsing from the branches of trees. The most recognizable feature of Stegosaurus were the bony plates on its back - these are usually depicted as standing upright, and were arranged in pairs or a zigzag fashion - however there are some scientists who believe the plates may have lain falt on the animal's skin. As well as the bony plates on its back, Stegosaurus also a number of spikes (the number varied depending on the particular species) at the end of its tail.

It is not entirely clear what purpose the bony plates served. One possibility is that they may have helped protect Stegosaurus from predators. Another idea is that because of their large surface area they might have been useful in temperature regulation - helping Stegosaurus to quickly warm itself up or cool itself down, depending on whether they were facing towards or away from the sun.

An average Stegosaurus was about 20 feet (6.1 meters) long, but some animals were considerably larger - the largest animals grew to a length of 30 feet (9.1 meters) and weighed around 2 tons.