The ornithischian, or bird-hipped dinosaurs, were herbivorous reptiles
which were quite varied in form and size and appear to have been more
highly developed than the saurischians. This order includes the
duck-billed dinosaurs (ornithopods), the plate-bearing dinosaurs
(stegosaurs), the armored dinosaurs (ankylosaurs), and the horned
dinosaurs (ceratopsians). Ornithischian tracks are known from Cretaceous
rocks in central and Trans-Pecos Texas.