Birds don't breathe like us mammals: instead of pushing air in and out of their lungs, they keep air flowing through a one-way system of sacs. As Science reports, new findings by biologists C. G. Farmer and Kent Sanders of the University of Utah show gators have a similar one-way respiratory system. The findings suggest that trait emerged in a common ancestor, and it could explain why dinosaurs came to dominate the planet all those millions of years ago.
Over the past 5 years, the two researchers tracked airflow patterns in the animals' lungs by using MRI scans on living gators and pushing fluids containing tracking agents through lungs removed from dissected specimens. In today's issue of Science, the pair reports that, like those of birds, alligator lungs also use one-directional airflow. Instead of moving into and out of air sacs as in mammals, the air flows continuously through the lungs. It enters the windpipe and moves through the lungs toward the tail, then back out the nostrils through the windpipe. The structure allows alligators, when they need it, to move a lot more air through their lungs and absorb a lot more oxygen than mammals can. The trait "is not unique to birds," Farmer says.
Farmer tells the Scientific American that this respiratory system helped archosaurs, the ancestors of dinosaurs, birds, and gators, sustain "vigorous exercise" despite the Triassic period's oxygen-poor atmosphere. (Oxygen levels reportedly dipped to 12% at the time, compared to 20% now.) Science quotes Adam Summers of the University of Washington as saying oxygen levels fell suddenly after a "major extinction event" 250 million years ago, and one-way respiration could explain why archosaurs "went from bit players to dinos" at the time.