That is because koalas have a special sound-producing organ not previously seen in any land-dwelling mammal, researchers say.
“In the larynx the vocal cords were normal, but outside there were these fleshy lips,” said David Reby, a researcher at the University of Sussex in England who was involved with the study, described in the journal Current Biology.
The fleshy lips are found in the koala’s soft palate, at the junction of the oral and nasal cavities.
Dr. Reby’s colleague Benjamin Charlton, the study’s lead author, inserted a pump and an endoscopic camera into the trachea of a euthanized koala in Australia to observe how the vocal folds vibrated and produced sound.
“When the koalas inhale they tense these lips, and it allows them to exaggerate their size through sound,” Dr. Reby said.
As a rule, an animal’s size reflects the dimensions of its vocal folds, which limit the lowest frequency an animal can reach. Smaller species tend to have calls with a higher frequency.
“The message here is that when there is a need to communicate something, evolution can lead to the emergence of new organs,” Dr. Reby said.