Stegosaurus is a dinosaur that lived approximately 165-136 million years ago, mainly during the Tithonian Jurassic Period. It is the largest and most famous known member of the Stegosaurs, an aptly-named race of armored dinosaurs known for their body plates and spikes. It is a character of Fantasia, appearing in the "Rite of Spring" segment.
Stegosaurus is one of many fauna in the sequence. It is unusually mixed in alongside species of the Permian, Triassic, Jurassic and Cretaceous periods. When the Tyrannosaurus first makes its appearance, the Stegosaurus is shocked like the many of them. As the Tyrannosaurus lunges for the herbivores, the Stegosaurus attempts an escape, but is slow in getting away from the dangerous beast, and resorts to fighting the Tyrannosaurus in an effort to save its own life. However, the battle comes to an end, with the Tyrannosaurus emerging victorious. The beast then proceeds to eat the fallen Stegosaur, as the scene becomes quiet and fades to black.
Later, other Stegosaurus appear in the group of dinosaurs marching through the drought. Some are trapped in a muddy pit with Apatosaurus and Diplodocus then they are killed by heat exhaustion and attacked by a group of desperately hungry Ceratosaurus.
- The Stegosaurus and its Stegosauridae relatives never coexisted with the Tyrannosaurus Rex, as they lived during different time periods spanning millions of years apart. The carnivorous theropods of that time were instead the Allosaurus, Saurophaganax, Ceratosaurus, and Torvosaurus.
- Stegosaurus has been found in both North America and Portugal; during the Jurassic Era, Portugal was a large island off the coast of North America, which allowed larger dinosaurs to colonize it.
- Despite its intelligent portrayal as a leader of a herd of herbivores, Stegosaurus has one of the smallest brains of any non-avian dinosaur proportionate to body size.
- The tail spikes of Stegosaurus (also known as Thagomizers) would measure approximately 1 meter in length. Although it's purpose is debated, evidence exists that they were used for defense. Fatal wounds have been found in Allosaurus skeletons that fit the tail spikes of Stegosaurus. This indicates Stegosaurus' flexible tail was able to move the tail spikes quickly to defend itself from carnivores. The structures may have also served as a form of display for species differentiation.
- Despite their great size, Stegosaurus' back plates were actually quite delicate; they were thin, full of blood vessels and covered in keratin (found in nails and hair as well as claws and horns). At one time, they were assumed to be used for warming up or cooling the animal down. They were probably more for display and species recognition than heat regulation or defense.
- According to a 2014-2015 study with S. Mjosi specimens, the back plates of some Stegosaurs were found to be round. These were attributed to being a male trait. The stereotypical pointed plates of Stegosaurs that most people are familiar with may have been a predominantly female trait.