Plates and Spikes: Stegosaurus had 17 bony plates that were embedded in its back. The plates ran along the Stegosaurus' back and tail in two rows, and the plates alternated in alignment. The function of these plates is uncertain. The plates were made of bone which was not solid, but was filled with tube-like tunnels. The plates were probably well-nourished by blood vessels, indicating that the plates may have been used to regulate the dinosaur's temperature. They may have also been used for protection or courting display purposes.

Stegosaurus also had tail spikes at the end of its flexible tail. These spikes were up to four feet long and were used for protection from predators. Different species of Stegosaurus had different numbers of tail spikes; Stegosaurus ungulatis had 8 spikes and Stegosaurus stenops had 4 spikes.

Anatomy: Stegosaurus measured up to 26-30 feet long (8-9 m), about 9 feet tall (2.75 m), and weighed about 6,800 pounds (3100 kg). Its skull was long and narrow; it had a toothless beak and small cheek teeth. Its head was carried close to the ground, probably no more than 3 feet (1 m) high.

Stegosaurus' rear legs were longer and straighter than its front legs, which sprawled out to the sides. The forefeet (the feet of the front legs) had five short, wide toes with short, hoof-like tips. The rear feet had three short, wide toes with hooves.

Fossils: Many fossils of Stegosaurus have been found in western North America, western Europe, southern India, China, and southern Africa. The first Stegosaurus fossil was found in 1876 by M. P. Felch. Paleontologist Othniel C. Marsh named Stegosaurus in 1877.