 Stegosaurus and related genera were herbivores . However , their teeth and jaws are very different from those of other herbivorous ornithischian dinosaurs , suggesting a different feeding strategy that is not yet well understood . The other ornithischians possessed teeth capable of grinding plant material and a jaw structure capable of movements in planes other than simply orthal ( i.e. not only the fused up @-@ down motion to which stegosaur jaws were likely limited ) . Unlike the sturdy jaws and grinding teeth common to its fellow ornithischians , Stegosaurus ( and all stegosaurians ) had small , peg @-@ shaped teeth that have been observed with horizontal wear facets associated with tooth @-@ food contact and their unusual jaws were probably capable of only orthal ( up @-@ down ) movements . Their teeth were " not tightly pressed together in a block for efficient grinding " , and no evidence in the fossil record of stegosaurians indicates use of gastroliths — the stone ( s ) some dinosaurs ( and some present @-@ day bird species ) ingested — to aid the grinding process , so how exactly Stegosaurus obtained and processed the amount of plant material required to sustain its size remains " poorly understood " . 
