A newly discovered rodent species belongs to a family thought to have been extinct for 11 million years.

Mark A. Klinger

Rodent Rises from the Dead

A rodent family long thought to exist only in fossilized remains turns out to be very much alive. This example of the "Lazarus effect," when an animal group known only from the fossil record reemerges thanks to the discovery of a living member, gives "invaluable insights" into our planet's biodiversity, past and present, researchers report 10 March in Science.

A few years ago, scientists surveying the biodiversity of Southeast Asia noticed an unfamiliar rodent that resembled a squirrel being sold as food in a Laotian marketplace. Apparently nocturnal, it lives in rocky limestone and thick vegetation and had stayed hidden from scientists for centuries. The team reported their find--a new species, genus, and family--in 2005. But to a group of paleontologists, led by Mary Dawson of the Carnegie Museum of Natural History in Pittsburgh, Pennsylvania, the rodent looked quite familiar. Upon reading descriptions of it, Dawson remembers thinking, "this is something we've known from the fossil record since 1974." Members of the family--called Diatomyidae--hadn't scampered on Earth for 11 million years, but Dawson had more than a hunch that the new rodent was part of the clan.

To confirm her suspicions, Dawson and colleagues compared several physical characteristics of the new rodent, dubbed Laonastes aenigmamus, to those of Diatomyidae. The teeth and jaws of these ancient rodents bore a striking resemblance to Laonastes. The positioning of the lower jaw, for example, was nearly identical, indicating a similar type of chewing motion. And the tooth enamel of old and new shared unusual patterns not found in other rodent species. Dawson says finding a living example of a fossilized family will help clear up some questions that bones can't always answer, such as how the rodents moved and what they ate.

The Lazarus finding is "very novel," says paleomammalogist Ross MacPhee of the American Museum of Natural History in New York City. "You really don't expect these creatures you work on to suddenly come to life again." MacPhee and paleontologist Lawrence Flynn of Harvard University both emphasize that the study underlines the importance of conserving ecological hot spots like the one where Laonastes was found in Southeast Asia. "It's another reason why we should be examining biodiversity today," says Flynn. "It's not true that, 'Gosh, everything's been discovered.'"

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