Dinosaurs first walked the earth 230 million years ago and dominated the land for 160 million years. They became extinct 65 million years ago during the Cretaceous period.
The three ages of the dinosaurs include the Triassic, Jurassic and Cretaceous. These periods fall under the Mesozoic Era, which lasted from 250 to 65 million years ago. Dinosaurs evolved from lizards known as archosaurs, having developed quadrupedal or bipedal posturing. It's believed that reptiles began exhibiting dinosaur and archosaur traits during the middle of the Triassic. Early dinosaurs can be categorized as therapods, bird-hipped dinosaurs and herbivores, among other categories. Therapods evolved into tyrannosaurs, Allosaurus, dino-birds and raptors. Herbivore dinosaurs existed in greater numbers than therapods. Bird-hipped dinosaurs included ornithopods and ankylosaurs.