This means that the lizard's breathing mechanism could be 270 million years old, 20 million years older than previously believed and 100 million years before the first birds appeared, according to findings published in the journal Nature.
Based on this timeline, dinosaurs may have breathed in a similar way. But lead author C.G. Farmer of the University of Utah cautions that the lizard's lungs have a different structure than bird and alligator lungs.
It is possible that this structure evolved 30 million years ago in its ancestors and 250 million years ago in archosaurs, the group that gave rise to birds, alligators and dinosaurs. Further research on other lizard species will help to explain this.
When a lizard takes a breath, air enters the windpipe and branches off into two primary airways. But, unlike humans and most other animals, the deoxygenated air does not flow back out the same way and loops around using tiny perforations in nearby lateral airways.
The researchers studied CT scans and 3D images of lungs from 10 deceased lizards, to visualize their anatomy. Savannah monitor lizards were used because their relatively large size made it easier to study the internal workings of their lungs.
Birds also have a similar breathing system, where they have a one-way loop mixed with some tidal airflow, the kind found in humans. Birds are thought to have these kind of lungs because of the strenuous nature of flying and the low concentration of oxygen at high altitudes. Having a one way system ensures the lungs are cleared of deoxygenated blood more efficiently.
[The University of Utah]