Lungs efficiently expel air: fin whale
Lungs of whales efficiently expel air via powerful exhalations.
"The mammals' dependency on air for breathing must be considered a real handicap in water, but the whale has minimised the problem by breathing even more efficiently than most mammals. Man only clears about 15% of the air in his lungs with a normal breath. The whale, in one of its roaring, spouting exhalations, gets rid of about 90% of its spent air. As a result it only has to take a breath at very long intervals. It also has in its muscles a particularly high concentration of a substance called myoglobin, that enables it to store oxygen. It is this constituent that gives whale meat its characteristic dark colour. With the help of these techniques, the fin-back whale, for example, can dive to depth of 500 metres and swim for forty minutes without drawing breath." (Attenborough 1979: 242)
Learn more about this functional adaptation.