Scientists found that a method of high-efficiency breathing used by birds is also employed by today's alligators, which share a common ancestor with dinosaurs.

In mammals, each fresh breath carries oxygen-rich air to "cul-de-sacs" in the lungs called alveoli.

Air circulating through these sacs transfers oxygen into the bloodstream that picks up the blood's carbon dioxide waste.

But birds don't have alveoli. Instead, the air flows in one direction into the birds' air sacs.

(Related: Meat-Eating Dinos Breathed Like Birds, Study Says.)

This adaptation keeps birds' lungs filled with "fresh" air, allowing them to breathe at altitudes that would kill other animals.

To find out how alligators breathe, scientists pumped fluids through the lungs of dead American alligators and measured the direction