Academic journal article The Science Teacher

Why Lizards Have Bird Breath

Academic journal article The Science Teacher

Why Lizards Have Bird Breath

Article excerpt

Whether birds are breathing in or out, air flows in a one-directional loop through their lungs. For decades biologists assumed this pattern was unique to birds, a special adaptation driven by the intense energy demands of flight.

But that view is wrong, according to University of Utah scientists who have shown that birdlike breathing also developed in green iguanas--reptiles not known for high-capacity aerobic fitness. The finding bolsters the case that unidirectional birdlike flow evolved long before the first birds, arising nearly 300 million years ago in a common ancestor of lizards, snakes, crocodiles, and dinosaurs.

"We thought we understood how these lungs work, but in fact most of us were completely wrong," says Colleen Farmer, an associate professor of biology and lead author of the new study published in Proceedings of the National Academy of Sciences. "People have made a lot of assumptions about how lungs work in animals such as reptiles and crocodiles, but they never actually measured flow," she says.

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In humans and other mammals, lungs have airways with a tree-like branching structure. A main trunk in each lung splits into branches and twigs. Air flows in and out in a tidal fashion. Oxygen and carbon dioxide pass to and from blood in tiny air sacs, called alveoli, at the tips of the smallest airway branches. …

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