Ornithischia is an order of beaked, herbivorousdinosaurs. They are known as the "bird-hipped" dinosaurs because of their hip structure, even though birds are actually descended from the "lizard-hipped" dinosaurs (the saurischians). They were also more numerous than the saurischians.
The Dinosauria supergroup was divided into the two orders, Ornithischia and Saurischia, by Professor Harry Seeley in 1887. The split is based on the form of the pelvis, braincase, vertebrae and armor, and has been generally adopted..
The ornithischian pubis bone points downward and toward the tail, while the saurischian pubis points downward, and towards the front. Ornithschians also had smaller holes in front of their eye sockets (antiorbital fenestrae) than saurischians, and a wider, more stable pelvis.
The ornithischians are further divided in the Thyreophora, which includes the armored Stegosaurus and Ankylosaurus; and the Cerapoda, which includes the frilled Triceratops, and duckbills like the Hadrosaurus. The Cerapoda is a relatively recent grouping (Sereno, 1986), and may be identical to (synonymous with) the older group, Ornithopoda.
External links
Ornithischia (http://www.palaeos.com/Vertebrates/Units/320Ornithischia/100.html#Ornithischia), from Palæos. (cladogram, characteristics)
Ornithischians are a well-defined group diagnosed by several unique evolutionary features; the entire group was analyzed cladistically in 1986, and a phylogeny was described that has been the basis of all later work.
Ornithischians have a predentary bone, a toothless, beaklike addition to the front of the lower jaw that, like the front of the upper jaw, probably had a horny covering in life.
Ornithischians have âcheek teethâ along the sides of the jaw, but never in the front; the bones at the front of the mouth sometimes developed into the horny beaks typical of modern turtles.
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