When wandering through a hunter's market in Laos, Robert Timmins of the Wildlife Conservation Society happened upon a previously unknown rodent. Called kha-nyou by locals--or rock rat--the long-whiskered and furry-tailed rodent was reputed to favor certain limestone terrain. Western scientists named it Laonastes aenigmamus or stone-dwelling enigmatic mouse--partially because a live specimen has never been collected--and thought the rock rat represented a new family of mammals. But new research reported in today's Science proves that Laonastes actually represents a fossil come to life.

Paleontologist Mary Dawson of the Carnegie Museum of Natural History and her team immediately recognized the strange rodent as a living member of a family thought to have been extinct for at least 11 million years: the Diatomyidae. Fossilized remnants of this group have been found throughout Asia with a distinctive jaw structure and molars. A new specimen of Diatomys discovered in June of last year in China bore an uncanny resemblance to Laonastes, including the same body size and tail span.

"It's the coelacanth of rodents," Dawson says, referring to the ancient fish believed extinct until a live specimen was hauled from the depths by South African fishermen. "One of the beautiful parts of this discovery was that we were able to correctly predict that Laonastes would have four roots in its molars just as in Diatomys."

The rock rat represents a rare opportunity to compare assumptions derived from the fossil record and an actual living specimen to determine overall accuracy of the techniques involved, the scientists argue. It also represents tantalizing support for the theory that many mammals evolved in Asia and later colonized other continents, as its closest living relative is the gundis--a guinea pig-like rodent of northern Africa.

Ultimately, kha-nyou provides a compelling argument for preservation efforts in Southeast Asia, joining tree shrews, flying lemurs and tarsiers as remnant populations of ancient mammal families in the region. "Laonastes is not the only new organism to be discovered in southeastern Asia," Dawson adds. "The highest priority must be given to preserving this unique biota and especially Laonastes while it is still possible."