Birds develop feathers the same way we develop hair and teeth

The hexagonal patterning of bird feather growth relies the same signaling pathway used to form hair, teeth, and scales in mammals, fish, and reptiles.

Do any birds have hair instead of feathers? If so, why? - Quora

This extinct bird boasted dinosaur-like teeth

How Did Birds First Take Off? - The New York Times

Are there any birds with teeth? - Quora

Fallen Angels: Birds of Paradise in Early Modern Europe – The Public Domain Review

Your Inner Feather

Feather evolution

Bird Feathers, Types, Parts & Anatomy

Scales or feathers? It all comes down to a few genes