New research conducted by C.G. Farmer, associate professor of biology at the University of Utah, and colleagues from the University of Utah and Harvard University and presented in the Dec. 11, 2013, issue of the journal Nature has found that one-way airflow in monitor lizards indicates that this method of respiration probably arose as early as 270 million years ago.
The researchers examined air flow in the lungs of African savanna monitor lizards (Varanus exanthematicus) with CT scans, autopsy of deceased animals, and airflow analysis.
The lizards have a one-way airflow in their lungs like birds and crocodiles. The air flows into the lungs and makes a loop through the lungs before exiting. One-way airflow allows birds to fly at high altitudes for long periods of time where the oxygen content is low relative to lower altitudes.
The researchers conclude that their discovery presents a potential time frame for the development of a similar one-way airflow in dinosaurs and reptiles that pushes the development of this type of respiration back in time by at least 20 million years.
The most probable first appearance of one-way airflow developed as early as 270 million years ago among cold-blooded diapsids. Diapsids were the common ancestors of the archosaurs and Lepidosauromorpha, a group of reptiles that today includes lizards, snakes and lizard-like animals known as tuataras. Birds are thought to have developed from archosaurs.
This development may have been an evolutionary adaptation to low oxygen levels on Earth at the time.