4 Feathers are homologous to reptile scales, with a dermal pulp and epidermal, keratinized features. Small hooklets on the barbules help to hold the vane together.
Bird skeletons are light and strong.
The skull has a reduced number of bones and a beak instead of teeth. The rest of the skeleton is also modified for flight. Many bones are fused, e.g., the synsacrum is a fusion of much of the posterior vertebral column to allow the bird to maintain the proper position for landing, etc. Perching tendons assist in holding the bird in place. The sternum is large, broad, and keeled, allowing for muscle attachment.