The majority efficient respiratory systems of all animals, like to that of modern diving birds like penguins, fossil proof shows. Bony projections on the ribcage known as uncinate process play a significant role in both respiration and locomotion. The little bones work as levers to move the ribs and sternum during breathing. They have become tailored in different type of birds to deal with different habits of getting around.

The bones are shortest in runners like emus that don't require large breast muscles for flight, in-between in flying birds and longest in divers such as the penguin. The Manchester team deliberates a wealth of fossil remains of dinosaurs and extinct birds such as Archaeopteryx, and compares these with skeletons of living birds. They found that uncinate processes are also found both in the destroyed ancestors of birds, the theropod dinosaurs, and in recent species.

Refer: http://news.bbc.co.uk/1/hi/sci/tech/7081166.stm