Evolution of birds

The evolutionary history of birds, tracing their origin among theropod dinosaurs and the diversification of lineages that survive today.

Theropoda: A major dinosaur group that includes birds and extinct carnivorous dinosaurs such as Tyrannosaurus. Birds evolved within theropods, making this dinosaur group their ancestral context.
Feather evolution: The evolutionary development of feathers from simpler integumentary structures into diverse forms. Feathers predate birds and were later adapted for insulation, display, and flight.
Cladistics: A method of classifying organisms by shared derived traits and patterns of common ancestry. Bird origins are reconstructed by placing fossil species on evolutionary branches.
Cretaceous–Paleogene extinction event: The mass extinction about 66 million years ago that eliminated non-avian dinosaurs and many other organisms. Its aftermath opened ecological opportunities for the bird lineages that survived.
Maniraptora: A group of theropod dinosaurs that includes birds and several close extinct relatives. Birds arose among maniraptoran dinosaurs, many of which had feathers.
Origin of flight: The evolutionary transition by which powered flight arose in a lineage of animals. Bird evolution includes the acquisition of powered flight, though its precise route remains debated.
Phylogenetics: The study of evolutionary relationships among organisms and the methods used to infer them. Competing phylogenetic analyses can place fossil birds and their relatives differently.
Neornithes: The crown group containing all living birds and their most recent common ancestor. All surviving bird diversity belongs to this lineage, which persisted beyond the end-Cretaceous extinction.
Archaeopteryx: A Late Jurassic feathered dinosaur with wings and a mix of birdlike and non-birdlike features. Its fossils preserve an early combination of traits associated with birds and theropods.
Bird wing: The forelimb of a bird, modified to generate lift and control during flight. Theropod forelimbs became wings through changes in feathers, bones, and movement.

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