[I] Feathers provided the irrefutable proof that birds evolved from dinosaurs.
Since then, a spectacular collection of small, feathered dinosaurs has been found in Liaoning and other places around the world, including every imaginable evolutionary step from small, fuzz-covered, carnivorous theropods to fully feathered and winged birds.
They began as simple fluffy filaments that were probably used to keep theropods warm – evidence supporting the theory that at least some dinosaurs were "warm-blooded." They could also have served as pieces of jewelry. Tethered with plumage, the plumage of the smaller theropods would have given them a certain boost to hunt flying insects.
This series of features – small with light bones, twisted shoulder cavities with a furcula, turbocharged breathing systems and feathers – was developed long before they blew up and formed the scene for Protobirds
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