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The secret songs of giant beavers

Scientists discover a noisemaking chamber in the extinct animal’s skull


Giant beavers, which vanished from North America about 10,000 years ago, had a secret in their heads: a long compartment that stretched from front to back in the animals’ skull. Caroline Rinaldi, a paleontologist who studies extinct mammals, may have figured out the chamber’s purpose. She recently presented her ideas to a meeting of scientists in Las Vegas, using a plastic copy of the skull’s hidden tunnel to demonstrate her surprising find.

She held the model to her lips and blew a note, producing a noise that Science News reporter Susan Milius described as “bleating.” The sound wasn’t pretty, but the demonstration showed that the hidden cavity made noise, and might have even helped the animal communicate.

The hidden passage had no opening to the outside of the skull and ran underneath the airway connecting the nose and throat. Where the two passageways touched, a long, skinny slit would have let air through. Sounds bouncing around inside the skull’s sinus cavities could have become louder.

In addition to bone, animals use soft tissues to vocalize. As a result, the sounds Rinaldi made at the meeting probably differed from the beaver cries last heard 10,000 years ago. “We don’t have the soft tissue,” she said. Soft tissue includes things like organs and membranes, which unlike bone are rarely preserved as fossils.

beaver passageway

The giant beaver lived up to its name, especially when compared with today’s dam-building beavers. The titanic rodents probably weighed 100-plus pounds, and some scientists say the beavers may have been as big as black bears. Their pointed, curved front teeth were as big around as quarters.

Despite coming from the same family, modern beavers won’t help scientists like Rinaldi solve mysteries about the giants. Their skulls are shaped differently. Giant beavers, along with other large animals, flourished during the last Ice Age, which started about 70,000 years ago and ended around the time the giant beaver went extinct. Many beasts alive during the time period looked like oversized versions of modern animals, but their bodies didn’t necessarily work in the same ways.

“It’s a great lesson that if you take a modern animal and scale it up, you’d be wrong,” Larry Flynn told Science News. Flynn, who did not work on the new giant beaver study, studies ancient rodents at the Peabody Museum of Archaeology and Ethnology at Harvard University. He told Science News that the giant beaver looked puny when compared with some of the other large rodents alive at the time. 

Rinaldi, a researcher at the University of Missouri-Kansas City School of Medicine, used CT scans of a giant beaver’s skull to create her plaster model. CT stands for computerized tomography, and CT scans are X-ray images taken from many different sides of an object to create a 3-D image of it. The hidden passage in the giant beaver’s head showed up on CT scans, and Rinaldi reported she’d never seen anything like it before.

“I don’t know of any other animal that has this,” she said.

POWER WORDS (adapted from the New Oxford American Dictionary)

CT scan A three-dimensional image made from X-ray images of an object taken from different angles.

X-ray Radiation of high energy and very short wavelength (between ultraviolet light and gamma rays) that is able to pass through many materials that block light.

paleontology The branch of science concerned with fossil animals and plants.

rodent A gnawing mammal of an order that includes rats, mice, squirrels, hamsters, porcupines and their relatives, distinguished by strong, constantly growing incisors and no canine teeth. They are the largest order of mammals.

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