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Ornithischia

2007 Schools Wikipedia Selection. Related subjects: Dinosaurs

   iOrnithischia

                      Fossil range: Triassic-Cretaceous

   Ornithischian pelvic structure (left side)
   Ornithischian pelvic structure (left side)

                             Conservation status

   Extinct (fossil)
                Scientific classification

   Kingdom:    Animalia
   Phylum:     Chordata
   Class:      Sauropsida
   Superorder: Dinosauria
   Order:      Ornithischia
               Seeley, 1888

                                  Suborders

   Thyreophora
   Ornithopoda
   Marginocephalia

   Ornithischia or Predentata is an order of beaked, herbivorous
   dinosaurs. The name ornithischia is derived from the Greek ornitheos
   (ορνιθειος) meaning 'of a bird' and ischion (ισχιον) meaning 'hip
   joint'. They are known as the 'bird-hipped' dinosaurs because of their
   bird-like hip structure, even though birds actually descended from the
   'lizard-hipped' dinosaurs (the saurischians). Being herbivores that
   sometimes lived in herds, they were more numerous than the
   saurischians. They were prey animals for the theropods and were smaller
   than the sauropods.

Characteristics

   Edmontosaurus pelvis (showing ornithischian structure - left side)
   Oxford University Museum of Natural History
   Enlarge
   Edmontosaurus pelvis (showing ornithischian structure - left side)
   Oxford University Museum of Natural History

   The Dinosauria superorder was divided into the two orders Ornithischia
   and Saurischia by Harry Seeley in 1887. This division, which has
   generally been accepted, is based on the evolution of the pelvis into a
   more bird-like structure (although birds did not descend from these
   dinosaurs), details in the vertebrae and armor and the possession of a
   'predentary' bone. The predentary is an extra bone in the front of the
   lower jaw, which extends the dentary (the main lower jaw bone). The
   predentary coincides with the premaxilla in the upper jaw. Together
   they form a beak-like apparatus used to clip off plant material.

   The ornithischian pubis bone points downward and toward the tail
   (backwards), parallel with the ischium, with a forward-pointing process
   to support the abdomen. This makes a four-pronged pelvic structure. In
   contrast to this, the saurischian pubis points downward and towards the
   head (forwards), as in ancestral lizard types. Ornithischians also had
   smaller holes in front of their eye sockets (antorbital fenestrae) than
   saurischians, and a wider, more stable pelvis. A bird-like pubis
   arrangement, parallel to the vertebral column, independently evolved
   three times in dinosaur evolution, namely in the ornithischians, the
   therizinosauroids and in bird-like dromaeosaurids.

Classification

   The ornithischians are further divided in the two clades: the first are
   the Thyreophora and the second the Cerapoda. The Thyreophora include
   the Stegosauria (like the armored Stegosaurus) and the Ankylosauria
   (like Ankylosaurus). The Cerapoda include the Marginocephalia (
   Ceratopsia like the frilled ceratopsidae and Pachycephalosauria) and
   the Ornithopoda (among which duck-bills (hadrosaurs) such as
   Edmontosaurus). The Cerapoda are a relatively recent grouping (Sereno,
   1986), and may conceivably be identical to (synonymous with) the older
   group, Ornithopoda: most of these divisions are not true by definition.

Taxonomy

   ORDER ORNITHISCHIA
     * Pisanosaurus
     * Family Fabrosauridae
     * Suborder Thyreophora - (armored dinosaurs)
          + Infraoder Stegosauria
          + Infraorder Ankylosauria
     * Cerapoda
          + Suborder Ornithopoda
               o Family Hypsilophodontidae
               o Infraorder Iguanodontia
                    # Family Hadrosauridae - (duck-billed dinosaurs)
          + Heterodontosauriformes
               o Family Heterodontosauridae
               o Suborder Marginocephalia
                    # Infraorder Pachycephalosauria
                    # Infraorder Ceratopsia - (horned dinosaurs)

   Retrieved from " http://en.wikipedia.org/wiki/Ornithischia"
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   with only minor checks and changes (see www.wikipedia.org for details
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