Scientists Put Alligators on a Treadmill

Scientists think they have found the answer to a question that has perplexed biologists for decades: How did dinosaurs run and breathe at the same time?

But finding the answer was a bit tricky. First, they had to train alligators to walk on a treadmill.

Since they couldn't study dinosaurs directly, they turned to the next best thing.

"Alligators are very closely related to dinosaurs," says Colleen Farmer, a research assistant professor of biology at the University of Utah. Modern alligators evolved about 95 million years ago, so they coexisted with dinosaurs, she says.

Breathing on the Move

Farmer and a colleague, David Carrier, an associate professor of biology at the university, discovered that gators are able to breathe while they walk because they use a rocking pubic bone, part of the pelvis, to expand and contract their breathing cavity. It seems likely, the researchers contend, that dinosaurs used a similar mechanism.

Otherwise, they would have suffered from the same limitation as lizards, which have to pause every few steps and take a deep breath because they can't run and breathe at the same time. If that held true for dinosaurs, they would have been very limited in their abilities, forced to wait patiently for dinner to come along instead of chasing it down.

"If you can find ways to run and breathe simultaneously, then you can be active for extended periods of time," says Carrier. Far from being sluggish and slow, the finding indicates that dinosaurs could have been as aggressive and active as modern mammals.

That isn't what the researchers had set out to discover. It's a serendipitous finding that grew out of research into how blood flows to the heart during exercise. To understand how that works in modern animals, Carrier says, you have to look at how animals evolved over millions of years. And where better to start than with dinosaurs?

Training Alligators to Work Out

So the researchers borrowed five young alligators from a wildlife refuge in Florida to see what they could tell them about their distant cousins.

"These are juveniles," Farmer emphasizes, but they range up to 3 feet long and that's big enough to cause a little damage. She admits she was nipped once by a smaller one, and while it didn't hurt, it got her attention.

"I'm much more careful around the larger ones," she says. Even the youngest gators have teeth, but "they aren't like a mammal's teeth that are designed for cutting or slicing. They are more designed for just grabbing on to prey."

It turned out that training them was pretty easy.

"They seem to be very smart animals," Farmer says. "You handle them gently and frequently, and they tame right down, almost like a parrot."

The treadmill is surrounded by a Plexiglas cage, so the animals can't jump off, and all it takes is a tap on the tail to get them moving.

Still, it took several months for them to learn to keep pace with the treadmill. They had to walk at about 1 mile per hour for three or four minutes to keep up with the movement of the belt, and they weren't exactly fitted out for a day at the beach.

The gators wore masks so the scientists could measure the oxygen they took in, and the carbon dioxide they exhaled, and how often and how deeply they inhaled and exhaled. And they were hooked up to wires that ran to electronic sensors that could tell which muscles were being used while they walked and breathed.

Belly Breathing Bones?

When humans and mammals breathe, the ribs lift upward and outward, expanding the chest volume. Simultaneously, the diaphragm contracts and moves down, further increasing the volume.

Carrier and Farmer found that when alligators inhale, certain muscles pull the pubic bone downward to expand the abdominal cavity.

"We stumbled into a mechanism that was actually quite surprising," Carrier says. "The pelvic girdle was playing a role in lung ventilation."

So what does that have to do with dinosaurs?

"Dinosaurs have an extra set of ribs that run along the belly, and the function of those ribs has remained an enigma," Farmer says. "Some people think they were to protect the belly and other people have speculated that maybe they played some role in breathing. Our work shed some light on that. They probably were actively employed in breathing."

The belly ribs were long and thin, and thus unlikely to have been part of the animal's protective armament, she adds. The ribs probably were attached to a rocking pelvic bone that moved, thus expanding the breathing cavity and allowing the animals to run and breathe at the same time.

Of course, a lot has changed since dinosaurs took their last breaths.

Alligators have opted for the simple life, preferring to lie in mucky water and wait for prey to come by instead of chasing it down. As "sit and wait predators," they don't really need that rocking pubic bone any more, but they still have it.

As for those five gators in Utah, they have to earn their daily ration of mice, goldfish and eggs by running on a treadmill for awhile longer. After the research project is over, they will be returned to the refuge in Florida to retire and bask in the sun.

Lee Dye’s column appears weekly on A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.