 The quadrupedal Stegosaurus is one of the most easily identifiable dinosaur genera , due to the distinctive double row of kite @-@ shaped plates rising vertically along the rounded back and the two pairs of long spikes extending horizontally near the end of the tail . Although large individuals could grow up to 9 m ( 29 @.@ 5 ft ) in length , the various species of Stegosaurus were dwarfed by their contemporaries , the giant sauropods . Some form of armor appears to have been necessary , as Stegosaurus species coexisted with large predatory theropod dinosaurs , such as Allosaurus and Ceratosaurus . 
