Dinosaurs are divided
into two groups
based on hip structure:
The Order Ornithischia
and
The Order Saurischia.

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ORNITHISCHIAN DINOSAURS
The Ornithischian dinosaurs had a hip structure similar to that of birds, but they were not the ancestors of birds. They outnumbered the Saurischians. The Ornithischians were vegetarian, and included two-legged, plated, armored, and horned dinosaurs. Major divisions of the Ornithischian dinosaurs: Pachycephalosaur
 Ornithopods
*Two-legged walk *No body armor *Spiked hand *Lived in the early Jurassic to Cretaceous
Thyreophorans ("shield bearers")
*Armored plates on the body *Lived in the early Jurassic to Cretaceous
Ceratopsians, horned dinosaurs
*Beaked *Lived during the Cretaceous
Pachycephalosaurs, dome-headed dinosaurs
 *Huge bony skulls *Lived during the Cretaceous

Theropods

basic theropod
*Led to the birds! *Fast and agile *Carnivorous diet *Sharp, slicing teeth and well-developed jaw muscles
*Clawed hands with three main digits *Bipedal walk *Strong legs with bird-like, three-toed, clawed feet
*Large eyes, indicating good eyesight. *pencil-shaped teeth *Usually walked on four legs *Largest land animals ever!

SAURISCHIAN DINOSAURS
The Saurischian dinosaurs (Order Saurischia) were the ancestors of
birds. They had a hip structure similar to that of lizards.
The Saurischians are divided into the
Sauropods, four-legged herbivores,
and the
Theropods, two-legged carnivores.
The oldest known dinosaurs, from the middle Triassic period, are Saurischians.
 Major divisions of the Saurischian dinosaurs:

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

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