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SALT LAKE CITY -- A University of Utah study of how alligators breathe may have turned up an important clue to explain why dinosaurs ruled the Earth for so long.
Scientists knew bird lungs were different from the lungs of mammals. The new study shows gators, too, have bird-like lungs.
C.G. Farmer, an evolutionary biologist at the University of Utah, discovered that alligators have a different lung architecture. He used three different methods to study how they do it.
"It is within the lung that there are loops, tubes that form loops," said Farmer.
This may be what allowed their common ancestors to dominate our ancestors for nearly 200 million years.
Mammal lungs are like an upside-down tree: incoming air spreads into thousands of tiny branches and dead-ends, until we exhale and reverse the flow.
But in alligators, the air doesn't just go in and straight back out. The air circulates in a sort of loop-de-loop of tubing before being exhaled. It never hits a dead end.
This structure has been shown to be more efficient at times when oxygen levels in the atmosphere are low.
"The same pattern of air flow is seen in the bird lung, and that pattern or air flow really increases the performance of the lung at high altitude or under conditions of low oxygen," said Farmer.
That may be one reason that ancestors to the alligator were set up to rule the Earth.
About the time dinosaurs took over, the atmosphere changed.
"The environment was very different in terms of the amount of oxygen that was available in the air," said Farmer. "It was about half of what we currently experience."
When oxygen levels were high, before about 245 million years ago, the ancestors of mammals ruled. When oxygen dropped, dinosaurs and other archosaurs took over. Until oxygen made a comeback 65 million years ago, mammals were generally the size of mice.
Farmer said, "We think this might explain why mammals were so small. They didn't have a lung that allowed them to fight or to sustain a race with these archosaurs."
Farmer's study was published Thursday in the journal "Science."
E-mail: hollenhorst@ksl.com
