Breathing like dinosaurs

		By Helen Briggs BBC News Online

Dinosaurs breathed like their modern-day relatives, the alligators, a new study suggests.

They were probably able to run and gasp in and out at the same time, unlike other reptiles, such as lizards, which must stop moving to breathe.

Many dinosaurs appear to have had an ability to be good endurance athletes

Dr Colleen Farmer, University of Utah

This would have given the dinosaurs, and prehistoric flying reptiles called pterosaurs, the endurance to lead an active lifestyle, say scientists in the United States.

The energy could have been crucial for hunting and migration, allowing dinosaurs to conquer the planet.

Dr Colleen Farmer, a biologist at the University of Utah, Salt Lake City, told BBC News Online: "An ability to simultaneously run and breathe is requisite to sustaining vigorous exercise.

"The ability to sustain vigorous exercise can impact life history traits such as foraging and migration.

"Thus, many dinosaurs appear to have had an ability to be good endurance athletes."

Common ancestor

The biologists studied alligators because they are thought to be among the closest living relatives of dinosaurs. The two groups once shared a common ancestor.

Dr Farmer and colleague David Carrier made their discovery by training five young American alligators to walk on a treadmill.

The alligators wore masks while walking so the researchers could measure how often and how deeply the animals inhaled and exhaled.

The alligators were trained to walk on a treadmill

Monitors were attached to determine which muscles the alligators used when breathing and walking, and to measure pressure in the abdomen.

The pair found that the alligator uses a mobile bone in its pelvis to help it take frequent deep breaths as it walks.

Dinosaurs had a similar bone structure, as do some birds which are thought by many scientists to be descended from dinosaurs.

"This is the first investigation of the importance of the pelvis to breathing in alligators," Dr Farmer told BBC News Online.

She added: "We have hypothesised that dinosaurs also used the pelvis to help them run and breathe simultaneously.

"This hypothesis is plausible due to both the close relationship of birds and alligators to extinct dinosaurs and due to the structure of the pelvic girdles of these dinosaurs."

Rocking action

The alligator has two modifications for breathing. It possesses a muscle attached to its liver, which pulls the organ back towards the tail when it inhales.

The liver is in turn attached to the lungs, which helps the alligator's chest and lungs expand and fill with air.

Flying reptiles called pterosaurs probably used a similar mechanism

When the alligator exhales, the liver slams forward into the lungs, forcing out the air. This breathing pump, known since the 1940s, acts together with the alligator's pelvis.

A hinge-like joint allows the bones in the pelvis to move rather than remain fixed. This rocking action enables the alligator's abdominal cavity to expand and contract, making room for the liver to move backwards and forwards.

This means blood can flow unimpeded from the tail back to the heart, giving the alligator more endurance.

However, modern-day alligators rarely use the extra endurance they have inherited. Instead, they prefer to lie in wait for unsuspecting prey, then pounce.

"Our hypothesis is dinosaurs were much more active and [alligators] have reverted back to a sit-and-wait lifestyle," said Dr Farmer.