Final answer:
The keel on a bird's sternum serves as an anchor for the flight muscles, enabling powerful wing movements necessary for flight. It is a bony extension where the pectoralis major and supracoracoideus muscles attach, allowing birds to have strong, controlled flapping essential for flying.
Step-by-step explanation:
The function of the keel on the sternum, or breastbone, in birds is crucial for flight. This blade-shaped structure provides an attachment point for the bird's powerful flight muscles. The flapping of the wings is achieved through the contraction of two main muscles: the pectoralis major, which moves the wings downward, and the supracoracoideus, which moves the wings upward. The keel's design, similar to that of a boat, allows these muscles to be anchored securely, accommodating their substantial size and facilitating the robust wing movements necessary for flight. Furthermore, the sternum of birds is deeper than in other vertebrates to house these large muscles, which contain abundant myoglobin for oxygen storage, an adaptation for the high metabolic demands of flight.