Stegosaurus (IPA: /ˌstɛgəˈsɔrəs/) is a genus of stegosaurid armoured dinosaur from the Late Jurassic period (late Kimmeridgian to Early Tithonian) in what is now western North America.
A large, heavily built, herbivorous quadruped, Stegosaurus had a distinctive and unusual posture, with a heavily arched back, short forelimbs, head held low to the ground and a stiffened tail held high in the air. Its array of plates and spikes has been the subject of much speculation. The spikes were most likely used for defense, while the plates have also been proposed as a defensive mechanism, as well as having display and thermoregulatory (heat control) functions. Stegosaurus was the largest of all the stegosaurians (bigger than genera such as Kentrosaurus and Huayangosaurus) and, although roughly bus-sized, it nonetheless shared many anatomical features (including the tail spines and plates) with the other stegosaurian genera. from Portugal, showing that they were present in Europe as well. Due to its distinctive tail spikes and plates, Stegosaurus is one of the most recognizable dinosaurs, along with Tyrannosaurus, Triceratops, and Apatosaurus. The name Stegosaurus means "roof-lizard" and is derived from the Greek στέγος-, stegos- ("roof") and σαῦρος, -sauros ("lizard"). At least three species have been identified in the upper Morrison Formation and are known from the remains of about 80 individuals. They lived some 150 to 145 million years ago, in an environment and time dominated by the giant sauropods Diplodocus, Camarasaurus, and Apatosaurus.