Some dinosaurs had feathers although they could not fly but birds have feathers that help them to fly. In the context of evolution, this means that:

Birds have evolved from reptiles

Reptiles had feathers but could not fly. Over time evolution kept on taking place and with evolution the body size changed and feathers got the ability to help in to flying. Reptiles kept on evolving and their evolution led to the formation of birds which could use feathers for flying. Thus birds have evolved from Reptiles.

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