When did the stegosaurus exist?

It is supposed that a lot of time ago,due to a meteorite collision with earth,the planet was surrounded with a huge cloud of dust so dense that sunlight was not able to reach the surface.Due to this plants and trees were not able to photosynthesize and eventually died,because of this vegetarian dinosaurs including the Stegosaurus died leading to the death of flesh eating dinosaurs that depended on vegetarian dinosaurs as their food.