Ornithischia is the order of dinosauria to which the stegosaurs belong. Ornithischian dinosaurs can be distinguished by a few characteristics common to the whole order. All ornithischian have their pubis rotated backwards against the ischium ( this resembles a bird hip), they all have a predentry bone; a palebral bone (above the eye ); a toothless roughened snout; a reduced anorbital opening; a jaw joint set below the level of the upper tooth row; cheek teeth with sub triangular crowns; at least five sacral vertebrae; ossified tendons above the sacral region; a small prepubic process along the pubis; and a long thin preacetabular process on the ileum. Lesothosaurs from the early Jurassic, are primitive ornithchians who well represent the features described above.
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These figures show the difference between the ornithischia hip ( far left ) and the saurichia hip ( left ). |
