An illustration imagines what the earliest diaphragm users might have looked like. Photo by Frederik Spindler/The New York Academy of Sciences

BONN, Germany, Nov. 18 (UPI) -- New analysis suggests the diaphragm -- the muscle, unique to mammals, that drives respiration -- evolved 50 million years earlier than previously thought.

The revelation comes in the wake of a re-examination of the physiology of caseids, a group of mammal-like reptiles living between 250 million and 300 million years ago.


Scientists have previously suggested caseids were poor breathers, their rib mobility limited by strong but inflexible joints. As a result, scientists assumed the animals were cow-like sedentary grazers.

But a reanalysis of caseid fossils showed the creatures likely spent most of their time in the water.

"The structure of the bone totally surprised me. They were sponge-like as in elderly," Christen Shelton, a researcher at the University of Bonn, said in a news release. "Suddenly, the barrel-shaped trunk with the short neck made sense. The paddle-like extremities were used for swimming."

The revelation -- detailed in the Annals of the New York Academy of Sciences -- forced scientists to rethink how caseids breathed.

"Aquatic vertebrates are specialists in quickly filling their lungs." explained Steven Perry, a zoologist at Bonn.

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Again, scientists concluded the ribs of caseids alone were not sufficient for powerful breathing -- the kind of breathing necessary for sucking in large gasps of air all at once. The only other logical explanation was the presence of a diaphragm.

Scientists concluded the last common ancestor linking caseids and mammals used a diaphragm to breathe some 300 million years ago, 50 million years earlier than previously thought.

Direct evidence of a diaphragm will likely never be found, so scientists must be willing to reason their way to an understanding of anatomical functionality based on bone evidence.

"We still don't know that much about these animals," added Bonn zoologist Markus Lambertz. "It has been a long way towards mammals, but the origin of the diaphragm marked a turning point on it."