How did the dinosaurs evolve?

How did dinosaurs evolve?

• Answer:

  Dinosaurs evolved from their earlier archosaur ancestors in the Triassic Period. The fundamental difference between dinosaurs and other reptiles is the structure of their hips. In most reptiles the legs are splayed out, limiting their locomotion. In dinosaurs they are erect and located on the underside of the body, allowing dinosaurs to have more stamina. Dinosaurs diverged from their archosaur ancestors approximately 230 million years ago in the Middle to Late Triassic Period. It is believed that Eoraptor ("dawn thief") represents the common ancestor of all dinosaurs. If this is so, the first dinosaurs were small, bipedal predators. As earlier forms of reptiles became extinct the dinosaurs grew and diversified, and became the dominant terrestrial animals throughout most of the Mesozoic Era. They occupied various niches. Some were small insectivores, some were vicious predators, and others were the giant sauropods.