Ornithischian Dinosaurs
Order: Ornithischia The name of this order means "bird-hipped," and refers to the pelvic structure of its included genuses. Oddly, modern birds are descended from saurischian ("lizard-hipped"), rather than ornithischian, dinosaurs!
Suborder: Ornithopoda As you can guess from this suborder's name (which means "bird-footed"), most ornithopods had birdlike, three-toed feet, as well as the birdlike hips typical of ornithischians. Ornithopods--which came into their own during the Cretaceous period--were quick, bipedal herbivores with stiff tails for balance, and many of them had primitive beaks. Examples of this populous suborder include Iguanodon, Edmontosaurus, and Heterodontosaurus. Hadrosaurs, or duck-billed dinosaurs, were a particularly populous type of ornithopod that dominated the Cretaceous period.
Suborder: Marginocephalia The dinosaurs in this suborder--which include Pachycephalosaurus and Triceratops--were distinguished by the odd structure of their skulls.
- Infraorder: Pachycephalosauria The name of this infraorder means "thick-headed," and that's not an exaggeration: pachycephalosaurs were characterized by their extremely thick, bony heads, which they presumably used to duel one another for the right to mate. These Cretaceous dinosaurs were mostly bipedal herbivores, though some may have been omnivorous. Examples include Pachycephalosaurus, Stygimoloch, and Stegoceras.
- Infraorder: Ceratopsia As pachycephalosaurs were distinguished by their skulls, ceratopsians were set apart by their horns and "frills"--some of which grew to gargantuan proportions, as in Triceratops and Styracosaurus. Ceratopsians often had thick, armored skin as well, probably because they needed to defend themselves against the carnivorous dinosaurs of the Cretaceous period. Otherwise, these large herbivores are thought to have been similar, behavior-wise, to modern elephants and rhinoceroses.
Suborder: Thyreophora This rather small suborder of ornithischians includes some rather large dinosaurs, including Stegosaurus and Ankylosaurus. Thyreophorans (the name means "shield bearers"), which include the ankylosaurs, were characterized by their elaborate spikes and plates, as well as their bludgeoning tails. Despite their fearsome armament--which they had most likely evolved for defensive purposes--they were herbivores rather than predators.
Next page: Aquatic Reptiles
