Stegosaurus was designated the official state fossil of Colorado in 1982. Colorado is where the very first stegosaurus fossil was found in 1876.
Stegosaurus (which means "roofed lizard" or "covered lizard") was a large herbivore that lived in Colorado during the Mid-Jurassic to the Late Cretaceous period. It had a tiny brain in its head (about the size of a walnut), but is thought to have possibly had a second brain as well that may have been the larger of the two.
In addition to the distinctive bony plates that formed a defensive ridge along the dinosaur's back and tail, stegosaurus had a unique and deadly defense against predators with its spiked tail, which it could apparently wield with great dexterity and accuracy. Besides providing armor, the plates are also thought to have possibly helped with regulating body temperature, and could have been used as a display (turning colors as a warning to predators and as part of its mating ritual).