Alligators breathe like birds

Alligators have a one-way path for breathing that is similar to birds’, new research shows. The findings, published in the Jan. 15 Science, could explain how  dinosaurs’ ancestors rose to prominence.

“It’s absolutely transformational,” comments Adam Summers of the University of Washington’s Friday Harbor Laboratories. “It really makes us think hard about our interpretations of anatomy.”

Unlike a mammal’s breath, which exits the lungs from the same dead-end chambers it enters, a bird’s breath takes a loopy one-way street through its lungs.

In mammals, air enters the lungs and flows through a network of branching tubes called bronchi, which culminate in small cul-de-sac chambers where blood vessels exchange carbon dioxide for oxygen. Air then exits the lungs via the same pathway.

But in birds’ lungs, air moves constantly through a simpler network of tubes, making a single circuit before being exhaled. This unidirectional flow makes gas transfer much more efficient — air can zip right past the blood vessels that need oxygen and then be on its way.

Conventional wisdom has held that only birds can do this because in addition to lungs, birds have air sacs that may steer the air unidirectionally through the lung. “People incorrectly believe that you must have avian-style air sacs in order to have unidirectional flow,” says C.G. Farmer of the University of Utah, a coauthor of the new study. “Alligators don’t have air sacs, so no one ever looked.”

Alligators have a one-way path for breathing that is similar to birds’, new research shows. The findings, published in the Jan. 15 Science, could explain how  dinosaurs’ ancestors rose to prominence.

“It’s absolutely transformational,” comments Adam Summers of the University of Washington’s Friday Harbor Laboratories. “It really makes us think hard about our interpretations of anatomy.”

Unlike a mammal’s breath, which exits the lungs from the same dead-end chambers it enters, a bird’s breath takes a loopy one-way street through its lungs.

In mammals, air enters the lungs and flows through a network of branching tubes called bronchi, which culminate in small cul-de-sac chambers where blood vessels exchange carbon dioxide for oxygen. Air then exits the lungs via the same pathway.

But in birds’ lungs, air moves constantly through a simpler network of tubes, making a single circuit before being exhaled. This unidirectional flow makes gas transfer much more efficient — air can zip right past the blood vessels that need oxygen and then be on its way.

Conventional wisdom has held that only birds can do this because in addition to lungs, birds have air sacs that may steer the air unidirectionally through the lung. “People incorrectly believe that you must have avian-style air sacs in order to have unidirectional flow,” says C.G. Farmer of the University of Utah, a coauthor of the new study. “Alligators don’t have air sacs, so no one ever looked.”