Chicago - (Reuters) - Alligators can stealthily maneuver through the water leaving nary a ripple, despite having neither fins nor flippers like other adept swimmers. Instead, they use special muscles to shift the position of their lungs, U.S. researchers said.

They said American alligators use their diaphragm, pelvic, abdominal and rib muscles to change their center of buoyancy, forcing the lungs toward the tail when they dive, toward the head when they surface, and sideways to roll.

"What this does is it gives the animal a way to change trajectory," said T.J. Uriona, a doctoral student at the University of Utah. "It allows them to quietly change how they are positioned in the water so they can strike," he said.

Uriona said the research offers a different theory on why alligators have diaphragm muscles, which are not common among reptiles.

He said the alligator's crocodilian ancestors in the Triassic period -- which started 250 million years ago -- were cat-sized land dwellers. Many researchers have assumed the diaphragm evolved to facilitate breathing while the animal was running.
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