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The evolution from dinosaurs to chickens happened gradually over millions of years. About 230 million years ago, the first dinosaurs appeared, and later one group of dinosaurs called theropods began to develop into a separate branch that eventually led to birds. Some theropods were small, walked on two legs, and gradually developed feathers. At first, feathers were probably used for keeping warm or attracting mates, but later they became useful for flying. About 150 million years ago, early bird