Which of the following structures are possessed by birds ONLY?

Feathers and a keeled sternum are distinct features that are unique to birds. Feathers are characteristic adaptations that enable birds to fly, regulate temperature, and provide camouflage. They represent a specialized form of skin modification, setting birds apart from all other animal groups.

The keeled sternum, or breastbone, serves as an anchor point for the powerful muscles that directly influence flight. Its structural adaptation allows birds to have an efficient flight mechanism, as the enlarged surface area provides more space for muscle attachment that is critical for the flapping motion required for flying.

Together, these two structures are defining characteristics of avian anatomy and reflect the evolutionary adaptations that have enabled birds to conquer an aerial lifestyle. Other groups of animals do not possess both feathers and a keeled sternum, making these traits exclusive to birds.