Stegosaurus is a genus of very large thyreophoran dinosaur in the family Stegosauridae which lived between 155 and 144 million years ago, during the Kimmeridgian to Tithonian stages of the late Jurassic period. Its fossils can be found in western North America. Aside from S. stenops, the type species of Stegosaurus, there are two other species: Stegosaurus ungulatus can be told apart by its pointed plates and longer leg and hip bones, while Stegosaurus sulcatus can be distinguished by the large bases and furrowed appearance of its proportionally bigger tail spikes. There may be a fourth species, Stegosaurus armatus, which is similar to S. sulcatus.
