And the keel-like protrusion on their sternums, where the flight muscles attach, shrinks or disappears, except in penguins, who repurpose their flight muscles and keels for swimming.

骨上龙骨状突起（行肌肉附着地方）会收缩或消失，但企鹅除外，行肌肉和龙骨重新用于游泳。