Alligators' muscles move lungs around for sneaky maneuvers in water

1 April 2008

Without a ripple in the water, alligators dive, surface or roll sideways, even though they lack flippers or fins. University of Utah biologists discovered gators maneuver silently by using their diaphragm, pelvic, abdominal and rib muscles to shift their lungs like internal floatation devices: toward the tail when they dive, toward the head when they surface and sideways when they roll. It allows them to navigate a watery environment without creating a lot of disturbance," says doctoral student T.J. Uriona. "This is probably really important while they are trying to sneak up on an animal but don't want to create ripples." The discovery in American alligators suggests "special muscles that manipulate the position of the lungs -- and thus the center of buoyancy -- may be an underappreciated but important means for other aquatic animals to maneuver in water without actively swimming," says C.G. Farmer, an assistant professor of biology. Those animals include crocodiles, African clawed frogs, some salamanders, turtles and manatees, she adds, noting that the use of muscles to move the lungs may be "incredibly important or you would not see it evolve repeatedly."

The researchers found that alligators are somewhat like pilots using controls to adjust an aircraft's pitch and roll, except the reptiles' controls are muscles that help them shift their lungs backward to dive, forward to surface or sideways to roll. Farmer says the new study asked how gators "manage to maneuver so gracefully without the fins and flippers used by fish, seals and other adept swimmers." "The secret to their aquatic agility lies in the use of several muscles, such as the diaphragmatic muscle, to shift the position of their lungs. The gases in the lungs buoy up the animal, but if shifted forward and backward cause the animal to pivot in a seesaw motion. When the animals displace gases to the right or left side of the body, they roll." Uriona says that during the Triassic Period, which began 250 million years ago, the crocodilian ancestors of alligators were cat-sized animals that lived only on land. "Until now, it was believed the diaphragmatic muscle evolved to help them breathe and run at the same time," he says. "Showing they are actually using it to move around in water gives an alternative explanation for why the muscle evolved." It also suggests the muscle didn't evolve until after crocodilians took to the water during the Cretaceous Period, which began 145 million years ago. During that time alligators' ancestors also evolved a flattened skull, shorter limbs and a big tail.

Science Daily
April 1, 2008

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