Ceratopsians are easily recognized by features of the skull . On the tip of a ceratopsian upper jaw is the rostral bone , an edentulous ( toothless ) ossification , unique to ceratopsians . Othniel Charles Marsh recognized and named this bone , which act as a mirror image of the predentary bone on the lower jaw . This ossification evolved to morphologically aid the mastication of plant matter . Along with the predentary bone , which form the tip of the lower jaw in all ornithischians , the rostral form 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 accentuated in later ceratopsians by the rearwards extension of the parietal and squamosal bones of the skull roof , to form the neck frill .