sentence2_structure: The bird ancestor<>lived<>in trees$$$wings<>is commonly associated<>with birds
sentence1: For example, the wings of birds, human arms, and pectoral fin in fish are all derived from a common ancestor In contrast, features that are similar because they have evolved in response to a common environmental pressure are said to be analogous.
sentence2: The bird ancestor that lived in trees developed wings, which is commonly associated with birds.
question: The bird ancestor that lived in trees developed what feature commonly associated with birds?