Stegosaurus is a genus of herbivorous, four-legged, thyreophorans from the Late Jurassic, characterized by the distinctive upright plates along their backs and spikes on their tails. Fossils of this dinosaur have been found in the western United States and in Portugal, where they are found in Kimmeridgian- to early Tithonian-aged strata, dating to between 155 and 150 million years ago. Of the species that have been classified in the upper Morrison Formation of the western US, only three are universally recognized: S. stenops, S. ungulatus and S. sulcatus. Stegosaurus would have lived alongside dinosaurs such as Apatosaurus, Diplodocus, Brachiosaurus, Allosaurus, and Ceratosaurus; the latter two may have preyed on it.