Stegosaurus lived at the end of the jurassic period, about 155-150 million years ago. It lived in the area that today is USA and Portugal, and was described for the first time in 1877.
The big plates of bone on the Stegosaurus´ back has confused many scientists. The first skeletons that were found were incomplete, and because of this it was hard to determine how stegosaurus actually looked. One of the first illustrations show it with plates of bone on the tail and spikes on its back.
Today we believe that Stegosaurus used the plates of bone to regulate its body heat, and also to show off and possibly attract a mate.
Stegosaurus is known for the small size of its brain compared to the size of its body. A stegosaurus weighing 4,5 tons may have had a brain weighing only 80 grams!