NASHVILLE, April 29 (UPI) -- U.S. scientists say they've found the shape of the cochlea -- a snail shell-shaped inner ear organ -- is important in low-frequency hearing.

Vanderbilt University researchers found the curvature of the cochlea, which converts sound waves into nerve impulses, is directly linked to the low frequency hearing limit of more than a dozen mammals.

Vanderbilt Assistant Professor Daphne Manoussaki, who led the study with Richard Chadwick of the National Institute on Deafness and Other Communication Disorders, said the relationship will be useful in estimating the impact noises of human activities have on animals that won't sit still for hearing tests. It also can provide new information about the hearing of extinct mammals, such as mammoths and saber-toothed tigers and might contribute insights into how the sense of hearing evolved.

"It turns out it is the curvature of the cochlea, not its size, is highly correlated to the low-frequency hearing limit," said Manoussaki, who noted spiral-shaped cochleae are exclusive to mammals. Birds and reptiles generally have plate-like or slightly curved versions, limiting the span of octaves that they can hear.

The study appeared this month in the Proceedings of the National Academy of Sciences.