New bird-dinosaur link: breathing method

The lungs of birds don't expand the way mammalian lungs do: they are air pumps, forcing air in and out of a series of air sacs anchored in small holes in the vertebrae, hips, and pelvis. This saves weight compared to having the large muscles and other structures involved in expanding the lungs. Now similar openings have been found in the bones of Aerosteon riocoloradensis, a large (9m long) dinosaur specimen from Argentina. The dinosaur was not a bird, but it breathed like one. Similar indications of air sacs have been found in the vertebrae of sauropods, but this discovery is the first in a carnivore and the first to include indications in the clavicles. It's one more link in the chain connecting birds to their ancestors, the dinosaurs.