Dinosaurs' superior lungs may have allowed them to outcompete early mammals, according to a new study of modern-day alligators.
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.
This adaptation keeps birds' lungs filled with "fresh" air, allowing them to breathe at altitudes that would kill other animals.