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.

These figures show the difference between the ornithischia hip ( far left ) and the saurichia hip ( left ).

general dinosaur anatomy

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