Lizards Breath In The Same Mysterious Way As Birds, Alligators, And Dinosaurs: Why One Way Loop Confuses Scientists

By Ajit Jha on December 11, 2013 1:03 PM EST

A Savannah Monitor Lizard
Savannah monitor lizards, like the one shown here, breath in the same strange way as birds and dinosaurs, according to a new study. (Photo: Shutterstock)

Birds, alligators, and, possibly, dinosaurs all share the same breathing method, called "one way loop." According to a University of Utah study, the breathing method is also shared by monitor lizards.

The study highlights the possibility that this type of breathing could have originated 270 million years ago, not 250 million years as believed earlier, and a full 100 million years before the first birds. "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.

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The study reveals not only that it the technique is not unique to birds to support strenuous activity such as flight but also that previous understanding about the function of this kind of breathing was inadequate. They exist in animals beyond those with fast metabolism, according to Farmer, who conducted the study along with two other University of Utah biologists, postdoctoral fellow Emma Schachner and doctoral student Robert Cieri, and James Butler, a Harvard University physiologist. The research was funded by American Association of Anatomists, the American Philosophical Society, the National Science Foundation and private donor Sharon Meyer.

Farmer recommends that study findings be interpreted cautiously. It is quite possible that one-way airflow evolved about 30 million years ago independently in the ancestors of monitor lizards and about 250 million years ago in archosaurs, the group that gave rise to alligators, dinosaurs, and birds. Scientists, however, do not know the reason for the emergence of this type of breathing.

Most animals, including humans, breath using a technique referred to as "tidal breathing," in which, air flow into the lungs moves progressively through bronchi and alveoli. There, oxygen enters the blood while carbon dioxide leaves the blood and enters the lungs. Air flows back the same way. In a 2010 paper, Farmer showed that unidirectional or one way breathing controlled by aerodynamic valves exist in alligators with the implication that this breathing pattern evolved 250 million years ago when crocodilians split away from the archosaur family tree.

One way looping flow was found in African savannah monitor lizards, Varanus exanthematicus, leading to the speculation that one-way airflow may have arisen not among the early archosaurs about 250 million years ago, but as early as 270 million years ago among cold-blooded diapsids. They were the common ancestor of a group of cold blooded reptiles including archosaurs and Lepidosauromorpha. Today, this reptilian group includes lizards, snakes and lizard-like creatures known as tuataras. 

One-way airflow helps birds to fly at high altitudes with low oxygen without passing out, according to Farmer. It was this breathing mechanism that probably helped the ancestors of dinosaurs to dominate the earth at a time when atmospheric oxygen levels were at their lowest 251 million years ago after the Permian-Triassic mass extinction. 

he study while solving some unanswered questions also raises some more questions. For instance, the unidirectional flow might have evolved under very high oxygen levels, according to Farmer, if it evolved in a common ancestor 20 million years earlier. This leaves us with a deeper mystery on the evolutionary origin of this breathing mechanism, according to Farmer. 

Image above courtesy of Shutterstock.

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