Air flows in one direction as it loops through the lungs of alligators, just as it does in birds. The study suggests this breathing method may have helped the dinosaurs' ancestors dominate Earth after the planet's worst mass extinction 251 million years ago.Such a breathing pattern likely evolved before 246 million years ago, when crocodilians split from the branch of the archosaur family tree that led to pterosaurs, dinosaurs and birds.
Image: C.G. Farmer & Kent Sanders, U. of Utah
Computerized tomographic (CT) X-ray images of side and top views of a 24-pound American alligator, with 3-D renderings of the bones and of airways or bronchi within the lungs. The windpipe and first-tier of bronchi are not shown. Air flows in one direction through a gator's lungs. It flows from the first-tier bronchi through second-tier bronchi (blue), then through tube-like third-tier parabronchi (not shown) and then back through other second-tier bronchi (forest green).This means that one-way airflow evolved in archosaurs earlier than once thought, and may explain why those animals came to dominance in the Early Triassic Period, after the extinction and when the recovering ecosystem was warm and dry, with oxygen levels perhaps as low as 12 percent of the air compared with 21 percent today.
Farmer emphasized the discovery does not explain why dinosaurs, which first arose roughly 230 million years ago, eventually outcompeted other archosaurs.
