Stegosaurus (/ˌstɛɡəˈsɔːrəs/) is a genus of armored dinosaur. Their fossil bones have been found in rocks dated to the Late Jurassic period (Kimmeridgian to early Tithonian ages), between 155 and 150 million years ago, in the western United States and Portugal. Several species have been classified in the upper Morrison Formation of the western U.S, though only three are universally recognized; S. stenops, S. ungulatus and S. sulcatus. The remains of over 80 individual animals of this genus have been found. Stegosaurus would have lived alongside dinosaurs such as Apatosaurus, Diplodocus, Brachiosaurus, Allosaurus, and Ceratosaurus; the latter two may have been predators of it.