Giant beavers had hidden vocal talents

Odd skull passages may have helped extinct rodent make sounds

LAS VEGAS – Blessed with a hidden chamber in their oversized skulls, extinct giant beavers may have created a unique Ice Age call of the wild.

Detailed CT scans reveal a dead-end passageway leading from the back of the animal’s skull toward its face. That chamber connects via a long, narrow slit to another passage going straight through the beaver’s skull from throat to nose, vertebrate paleontologist Caroline Rinaldi reported November 2 at a meeting of the Society of Vertebrate Paleontology.

“I don’t know of any other animal that has this,” said Rinaldi, of the University of Missouri-Kansas City School of Medicine.

Estimates of how big an animal the beaver Castoroides ohioensiswas have ranged from a sizeable 60 kilograms on up to the bulk of modern black bear. The last giant beaver died roughly 10,000 years ago, about the time many supersized creatures of the last Ice Age went extinct.

The beaver’s closed-at-the nose, partial airway doesn’t seem useful for breathing, Rinaldi said. She and her colleagues speculate that giant beavers whooshed air through it to create sounds.

What those sounds were is another puzzle. Rinaldi arrived at the paleontology meeting with a plastic model of the giant beaver’s inner airways, created using data from the CT scans. She could be coaxed to blow into it, producing a bleating sound reminiscent of a student’s first attempt at playing a wind instrument. “We don’t have the soft tissue,” Rinaldi lamented.

Her best guess, she said, is that the animal closed off the back of the complete airway and forced a breath through the dead-end passage. Air sped up when pushed through the long narrow slit, and soft membranes there may have created vibrations much like the reed of a wind instrument.

The beaver’s sinuses could have given considerable resonance to the sound, as the enormous cavities extended over the front of the brain and well into the cheeks. Rushing whirs, rumblings or maybe even whistles might have conveyed giant messages.

Today’s beavers aren’t much help in recreating the airway function because they don’t have the skull structures of the extinct giants. “It’s a great lesson that if you take a modern animal and scale it up, you’d be wrong,” said rodent paleontologist Larry Flynn, of the Peabody Museum of Archaeology and Ethnology at Harvard University.

Giant beavers probably lived in water but didn’t gnaw down trees and build dams, Rinaldi said. The giants’ front teeth, each about the size of a quarter in cross section, probably worked more like down-curved tusks than the chisel-like incisors of modern beavers.

Rinaldi turns to today’s hippopotamus for inspiration: The hippo doesn’t have a secret skull airway, but it does face the challenge of communicating both in air and water. Hippos, though not renowned musicians, make quite a range of sounds, from clicks to rumbles and grunts.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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