Dinosaur Classification - Enchanted Learning Software

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What are Taxonomy and Cladistics	How Are Dinosaurs Classified?			Dinosaur Genera	Not Dinosaurs, but Old and Interesting
	Major Dinosaur Families	Saurischian Dinosaurs "Lizard-Hipped"	Ornithischian Dinosaurs "Bird-Hipped"	Dinosaur Cladogram

How Are Dinosaurs Classified?
Dinosaurs were reptiles from the Mesozoic Era. They are classified as follows:

Kingdom Animalia (animals)
Phylum Chordata (having a hollow nerve chord ending in a brain)
Class Archosauria (diapsids with socket-set teeth, etc.)
Subclass Ornithodira (dinosaurs and pterosaurs)
Superorder Dinosauria (dinosaurs)
Order Saurischia and Ornithischia (based on hip structure)

Dinosaurs are divided into two orders based on their hip (pelvic) structure:

the "Lizard-Hipped" or Saurischian dinosaurs
the "Bird-Hipped" or Ornithischian dinosaurs.

Harry Seeley, a British scientist, divided the dinosaurs and named the two groups in 1887.

The pubis bone (part of the structure of the hip) points downwards and to the front in the Saurischians and points downwards and toward the tail in Ornithischians (opisthopubic condition). The Ornithischian pelvis is wider than the Saurischian pelvis. This may have made Ornithischians more stable while moving.

Saurischians Order Saurischia	Ornithischians Order Ornithischia


"Lizard-Hipped" dinosaurs (Saurischians) had a hip structure similar to that of lizards. Oddly enough, these "Lizard-Hipped" dinosaurs were the ancestors of the birds. Other anatomical features that characterize saurischians include an opening below the nostrils (called the subnarial foramen), an elongation on some neck vertebrae (resulting in long necks), a big thumb, an extra, wedge-shaped ankle bone (the astragalus), and many other distinctive features. The oldest known dinosaurs are Saurischians from the mid-Triassic period, about 230 million years ago. Saurischians included both meat and plant eaters.	"Bird-Hipped" dinosaurs (Ornithischians) had a hip structure that is similar to that of birds (but did not lead to the birds). They also had beak-like bone in the lower jaw in front of the teeth, called a predentary. Other anatomical differences include a narrow palebral (the bone that crosses the outside of the eye socket), and bony (ossified) tendons above the sacral area of the vertebrae. The Ornithischian dinosaurs were vegetarians and included plated, armored, and horned dinosaurs.
Example of "Lizard-Hipped" dinosaurs include: Theropods - bipedal carnivores like T. rex, Velociraptor, Compsognathus, and Deinonychus Sauropodomorphas - quadrupedal herbivores like Apatosaurus, Brachiosaurus, and Diplodocus.	Example of "Bird-Hipped" dinosaurs include: Ornithopods - Hadrosaurs (Maiasaura, Parasaurolophus), Hypsilophodontids, Iguanodontids, Fabrosauria (= lesothosauria, primitive ornithopods). Marginocephalia - Ceratopsians (Triceratops, Styracosaurus, etc.), Pachycephalosauria (Stegoceras, Pachycephalosaurus, etc.) Thyreophora (or Enoplosauria) - Stegosaurids, Ankylosaurids.