Dinosaurs are divided into two groups based on hip structure, the Order Ornithischia and the Order Saurischia. The Saurischian dinosaurs (Order Saurischia) were the ancestors of birds. They had a hip structure similar to that of lizards - the pubis bone pointed downwards and forwards. Saurischian skulls also have large, pronounced openings (antorbital fenestrae) between the eye socket and the nares (nostrils), much more so than the ornithischians. The Saurischians are divided into the sauropodomorpha, four-legged herbivores, and the theropods, two-legged carnivores. The oldest known dinosaurs (Eoraptor and Herrerasaurus) are Saurischians, and date from the mid- to late-Triassic period, about 230 million years ago.

Major divisions of the Saurischian dinosaurs:

SAUROPODOMORPHA Plant eaters Small heads with spatulate or pencil-shaped teeth Usually walked on four legs Largest land animals ever!

THEROPODS Led to the birds! Fast and agile Carnivorous diet Sharp, slicing teeth or beak, and well-developed jaw muscles Clawed hands (usually with three main digits - exceptions include the Tyrannosaurids, who lost the third digit) Bipedal walk Strong legs with bird-like, clawed feet Large eyes, indicating good eyesight.

The following is a sampling of Saurischian dinosaurs.

Sauropodomorpha (4-legged herbivores)
Prosauropoda (4-legged herbivores)
MASSOSPONDYLUS	PLATEOSAURUS	RIOJASAURUS
Sauropoda (large, 4-legged herbivores)
AMARGASAURUS	APATOSAURUS	BRACHIOSAURUS

CAMARASAURUS

DIPLODOCUS

SUPERSAURUS

ULTRASAUROS

ZIGONGOSAURUS

Theropoda ("Beast-footed", 2-legged carnivores, evolved into the birds)
ALBERTOSAURUS	ALLOSAURUS	BARYONYX

CARCHARODONTOSAURUS

CAUDIPTERYX

COELOPHYSIS

COMPSOGNATHUS	DEINONYCHUS antirrhopus	DILOPHOSAURUS
EORAPTOR	GALLIMIMUS	GIGANOTOSAURUS carolinii

MEGALOSAURUS	ORNITHOLESTES	ORNITHOMIMUS
OVIRAPTOR	PROTARCHAEOPTERYX	SALTOPUS

SCIPIONYX	SINOSAUROPTERYX	SPINOSAURUS
TROODON	TYRANNOSAURUS rex	UNENLAGIA comahuensis
UTAHRAPTOR	VELOCIRAPTOR	YANGCHUANOSAURUS

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