skeleton of stegosaurus armatus. stegosaurus is a genus of stegosaurid armoured dinosaur from the late jurassic period in what is now western north america. due to its distinctive tail spikes and plates, stegosaurus is one of the most recognizable dinosaurs, along with tyrannosaurus, triceratops, and apatosaurus. they lived some 155 to 145 million years ago. a large, heavily built, herbivorous quadruped, stegosaurus had a distinctive and unusual posture, with a heavily arched back, short forelim