Monitor lizards breathe by taking in air that flows through their lungs in a one-way loop -- a pattern of breathing that may have originated 270 million years ago in the ancestral group that gave rise to dinosaurs, and eventually alligators and birds, a new study finds.
Researchers at the University of Utah, in Salt Lake City, and Harvard University, in Cambridge, Mass., studied unidirectional breathing in monitor lizards, which can be found throughout Africa, China, India and other parts of Southeast Asia. Their findings suggest one-way airflow breathing may have evolved earlier than scientists had thought.
The researchers examined lungs from living and deceased monitor lizards, and found that when these large, often-colorful, carnivorous reptiles breathe, the airflow through their lungs is mostly one-way, unlike in humans and other mammals, which have a "tidal," or two-way, breathing pattern. Human lungs consist of a network of tubes that branch out into progressively smaller airways. Tidal breathing means air enters the lungs through these airways and then flows back out again the same way.
One-way airflow in birds was first suggested in the 1930s, said Colleen Farmer, an associate professor of biology at the University of Utah and senior author of the new study. [Images: Exotic Lizards Pop Out of the Ground in Florida]
"It was first noted in birds that were living in train stations in Europe," Farmer told LiveScience. "They were burning coal to power trains and noticed that only one part of the bird's lung was getting black with soot."
This method of breathing was thought to have evolved in birds to help them extract higher amounts of oxygen from their environment. Since air travels in only one direction through birds' lungs, more oxygen is transferred through their respiratory systems with each breath, which enables them to fly at high altitudes, where oxygen levels are low, without getting winded or passing out.