Powerful and squat stegosaurs are now one of the most recognizable dinosaurs: they are easily identified by the spines on the tail and the bony plates on the back—osteoderms. The representatives of this group lived about 165-125 million years ago, during the Jurassic and early Cretaceous periods. They were five to seven meters long and had a disproportionately small head. Their teeth were therefore quite small—about a centimeter in height and about the same in width.