A bizarre rodent that was discovered last year in a remote region of south-east Asia has turned out to belong to a family of mammals that was thought to have gone extinct more than 11 million years ago, a study has found.
A new analysis of the rodent's remains indicates that it is a striking example of the "Lazarus effect", when members of a species thought to be extinct are found living in an isolated part of the world.
The animal, called Laonastes aenigmamus, was identified last year by scientists who recognised it as a new species from dead specimens trapped in the wild and sold as food in the markets of Laos.
Laonastes was so unusual - not quite a rat or squirrel but not a guinea pig - that it was classified as the only living member of an entirely new mammal family, a rare honour in zoology.
However, Mary Dawson and Chris Beard at the Carnegie Museum of Natural History have looked deep into the mouth of Laonastes and found that its teeth are remarkably similar to those belonging to a family of Asian mammals called Diatomyidae which went extinct 11 million years ago.
"We knew exactly what we were looking at. The teeth were the most telling sign. We were sure we were looking at living Diatomyidae," Dr Beard said.
It is unusual for scientists to identify a living member of an extinct group of animals. The most famous example of the Lazarus effect was the capture of a live prehistoric fish called a coelacanth by fishermen off the east coast of South Africa in 1938.
Dr Dawson said that placing Laonastes in the Diatomyidae family of rodents is just as unusual given that the Lazarus effect in mammals only usually extends back no more than a few thousand years.
"It is an amazing discovery and it's the coelacanth of rodents. It's the first time in the study of mammals that scientists have found a living fossil of a group that's thought to be extinct for roughly 11 million years," Dr Dawson said. "That's quite a gap. Previous mammals had a gap of only a few thousand to just over a million years," she said.
The study, published in the journal Science, found that Laonastes and Diatomyidae share dental features such as molars with four roots and incisors with unusual microscopic structures etched into the enamel.
Paula Jenkins, the mammal specialist at the Natural History Museum in London, who initially described Laonastes, said the new research is fascinating, important and supported by convincing evidence.
"The idea of Laonastes as an example of the Lazarus effect is incredibly exciting and inspiring. It is very rare for a species believed to be extinct to show the Lazarus effect," Dr Jenkins said.
The identification of Laonastes was done with the help of the remains of 15 specimens which had all been collected by local hunters. There were also five skull fragments retrieved from regurgitated owl pellets.
"I would expect these specimens of Laonastes to be studied again and again and for their evolutionary relationships to be subjected to intense scrutiny," she said. "It would be surprising if the theory advanced in this paper were to remain unchallenged in future years, but that is what is so exciting about science."
Laonastes, known locally as Kha-Nyou, has never been observed in the wild and is believed to be a shy, nocturnal creature whose way of life is under threat. "It's the sole survivor of a very distinctive family of rodents with deep evolutionary roots in Asia. Every effort should be made to protect and preserve the living Laonastes," Dr Beard said.
Back from the dead
COELACANTH - Thought to have become extinct 80 million years ago. Found again in 1938
MADEIRAN LAND SNAIL (Discus guerinianus) - Extinct in 1996. Found again in 1999
FERNANDINA RICE RAT (Nesoryzomys fernandinae) - Extinct in 1996. Found again in late 1990s
IVORY-BILLED WOODPECKER (Campephilus principalis) - Extinct in 1944. Sighted in 1999, found again in 2005.
MOUNT DIABLO BUCKWHEAT (Eriogonom truncatum) - Extinct around 1935. Found again in 2005
JERDON'S COURSER WADER (Rhinoptilus bitorquatus) from India, assumed extinct until 1986.
LORD HOWE ISLAND STICK INSECT (Dryococelus australis) - Thought extinct from about 1918, rediscovered in 2001.
BAVARIAN PINE VOLE (Microtus bavaricus) - Rediscoverd in Austria in 2001.
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