 In the past , some palaeontologists , notably Robert Bakker , have speculated that the plates may have been mobile to some degree , although others disagree . Bakker suggested the plates were the bony cores of pointed horn @-@ covered plates that a Stegosaurus could flip from one side to another to present a predator with an array of spikes and blades that would impede it from closing sufficiently to attack the Stegosaurus effectively . The plates would naturally sag to the sides of the Stegosaurus , the length of the plates reflecting the width of the animal at that point along its spine . His reasoning for these plates to be covered in horn is that the surface fossilized plates have a resemblance to the bony cores of horns in other animals known or thought to bear horns , and his reasoning for the plates to be defensive in nature is that the plates had insufficient width for them to stand erect easily in such a manner as to be useful in display without continuous muscular effort . S. stenops also had disk @-@ shaped plates , on its hips . 
