rodent 'missing' for 11 million years

discovered in Laos

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.