How are bats and birds related?

Bats and birds are not closely related. Both are vertebrates and amniotes, but beyond this, they are quite distinct.

Birds are in the class Aves, characterized by feathers, beaks, and wings, while bats are in the order Chiroptera, within the class Mammalia. Bats are the only mammals with powered flight.

Bats and birds share a common ancestor, called the Synapsid, which existed around 300 million years ago. From this common ancestor, two branches diverged: the synapsids, which evolved into mammals, and the sauropsids, which gave rise to reptiles and birds.

While they may have shared a common ancestor, bats and birds have evolved significant differences in their anatomy, physiology, and behavior over millions of years.