 <unk> are easily recognized by features of the skull . On the tip of a ceratopsian upper jaw is the rostral bone , an <unk> ( toothless ) ossification , unique to ceratopsians . Othniel Charles Marsh recognized and named this bone , which acts as a mirror image of the <unk> bone on the lower jaw . This ossification evolved to <unk> aid the <unk> of plant matter . Along with the <unk> bone , which forms the tip of the lower jaw in all ornithischians , the rostral forms a superficially parrot @-@ like beak . Also , the jugal bones below the eye are very tall and flare out sideways , making the skull appear somewhat triangular when viewed from above . This triangular appearance is <unk> in later ceratopsians by the <unk> extension of the parietal and <unk> bones of the skull roof , to form the neck frill . 
