The dinosaurs were a group of reptiles that appeared about 215 million years ago during the Triassic Period. They survived for about 150 million years until the end of the Cretaceous Period.
Based on their anatomy, dinosaurs can be separated into two orders, the Saurischia ("lizard-hipped") and the Ornithischia ("bird-hipped"). Saurischia includes the bipedal, carnivorous Theropods and the massive plant-eating Sauropods. Ornithischia includes most other herbivorous dinosaurs such as the horned Ceratopsians, duck-billed Hadrosaurs, and armored Ankylosaurs. The dinosaurs were very successful and diverse until their mysterious extinction 65 million years ago.
Laramie Formation, Colorado - Theropod track