Microraptor, which was about the size of a crow, lived about 125 million years ago. Some elements of the Protopteryx wing bone and muscle structure match those of modern birds, said Zhang and Zhou, but the wing retains a claw found on some primitive birdlike animals. In modern birds, that claw has disappeared and been replaced with a structure that adds lift to the wing. Nonetheless, Protopteryx is thought to have been a competent flier. Most dinosaur researchers believe birds evolved 150 to 180 million years ago from a dinosaur group called Theropods.
Researchers cite fundamental skeleton similarities to support the theory.
The evolution of feathers, however, has been less clear. Some experts believe feathers evolved specifically to support flight, while others say feathers evolved first to provide warmth or protection from water. Fossils of three theropods bear hairlike images that some say could be the early precursors to feathers. It is clear they evolved from elongated scales. Dino fuzz has nothing to do with feathers.