Lizard Breath Evolved Before Dinosaurs, New Study Finds

The one-loop breathing method of monitor lizards is similar to that of birds, alligators and probably dinosaurs, raising questions about the evolution of this breathing technique, according to University of Utah researchers.

In a recent press release, researchers suggest that the one-loop breathing technique originated as early as 270 million years ago, which is nearly 20 million years earlier than previously believed. However, researchers have not been able to determine what led to the evolution of this breathing method.

"It appears to be much more common and ancient than anyone thought," said C.G. Farmer, the study's senior author and an associate professor of biology at the University of Utah. "It has been thought to be important for enabling birds to support strenuous activity, such as flight. We now know it's not unique to birds. It shows our previous notions about the function of these one-way patterns of airflow are inadequate.  They are found in animals besides those with fast metabolisms."

Farmer and her team also noted the possibility that since lizards have different lung structures than alligators and dinosaurs, the one-way airflow may have evolved independently about 30 million years ago in the ancestors of monitor lizards and about 250 million years ago in the archosaurs, the group that gave rise to alligators, dinosaurs and birds.

Previously, it was believed that this breathing technique helped dinosaurs thrive on Earth after the Permian-Triassic mass extinction when oxygen levels were the lowest on the planet.

"But if it evolved in a common ancestor 20 million years earlier, this unidirectional flow would have evolved under very high oxygen levels," Farmer said. "And so we are left with a deeper mystery on the evolutionary origin of one-way airflow."

For the study, researchers performed CT scans and made 3-D images of lizard lungs to visualize the anatomy of the lungs. They then pumped air in and out of the lungs to measure airflow. Later they pumped water laden with sunflower pollen particles or plastic microspheres through lizard lungs which showed unidirectional airflow in the lungs.

Humans and birds have very different breathing methods. In humans, air flows into the lungs' airway known as the bronchi till it reaches small chambers in the body known as Alveoli. Here the oxygen from the air is mixed with the blood, while the carbon dioxide is pushed back into the lungs and breathed out. It is more of a two way process.  Contrarily, in birds the air flows into air sacs in the lungs. It makes a loop there and is breathed out from the organ directly, without making its way to any other chamber. This breathing pattern works wells for birds, allowing them to fly at high altitudes where oxygen levels are low, without passing out.  Scientists believe the one-way breathing is an evolutionary trait to help birds absorb higher amounts of oxygen from their environment.

 "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."