Alligators betray their distant ancestral roots by breathing like birds, scientists have discovered.
Researchers found that, just as it does in birds, air flows in one direction as it loops through the lungs of alligators.
The breathing method is believed to have first appeared in ancient reptiles called archosaurs which dominated the Earth 251 million years ago.
In contrast, mammalian breath flows in and out of branching cul-de-sacs in the lungs called alveoli.
Archosaurs evolved along two different paths, one of which gave rise to the crocodilian ancestors of crocodiles and alligators. The other produced the flying pterosaurs and eventually birds.
The research on alligators suggests that bird-like breathing probably evolved earlier than previously thought, before the archosaur split.
It may explain why archosaurs became so dominant in the Early Triassic Period which followed a devastating mass extinction known as the ‘Great Dying’.
Prior to the extinction event, which killed off 70% of all land life and 96% of sea life, reptile-like mammals called synapsids were the largest animals on Earth.
After it, mammals were overshadowed by reptiles in the form of archosaurs and, later, dinosaurs.
As the Earth recovered from the ‘Great Dying’ conditions were warm and dry, with oxygen levels almost half what they are today.
But despite the lack of oxygen many archosaurs were capable of vigorous activity.
‘Lung design may have played a key role in this capacity because the lung is the first step in the cascade of oxygen from the atmosphere to the animal’s tissues, where it is used to burn fuel for energy,’ said lead researcher Colleen Farmer, from the University of Utah in Salt Lake City, US.