BioEd Online

A family of rodents thought to have died out some 11 million years ago has a descendent alive and well and scampering around Asia.

The rodent, which is grey and squirrel-like, with a bushy tail, was discovered last year being sold for food in the markets of Laos. The locals call it the Kha-nyou; scientists christened it Laonastes aenigmamus¹.

The little animal drew attention at the time because it was so different from other rodents that it was thought to represent a new family of mammals, which the scientists called Laonastidae.

But when palaeontologist Mary Dawson at the Carnegie Museum of Natural History, Pittsburgh, saw the animal she thought otherwise. She saw that it was similar to the fossils of ancient rodents called Diatomyidae, which once lived in south and east Asia. She thought that Laonastes might be a descendant of these creatures.

From menu to museum

To confirm her suspicions, Dawson and her colleagues compared Laonastes with the fossil remains of Diatomys shantungensis, a Diatomyid rodent that lived some 18-20 million years ago.

The results support the idea that the two animals belong in the same family, Dawson's team reports in Science². Their teeth, for example, have similar enamel, and some have the same four characteristic roots.

The discovery is an example of the 'Lazarus effect' - after the Biblical character resurrected by Jesus - in which an animal reappears in the fossil record or the flesh after it was thought to be extinct.

Laonastes is a particularly unusual case of the Lazarus effect, experts say, because it is a mammal and because the descendant was found alive.

The discovery begs the question of what this family of animals was doing for 11 million years to escape human detection. The likelihood is that the Kha-nyou has been hidden away in a small, remote pocket of Southeast Asia, says Ross McPhee who studies mammalian fossils at the American Museum of Natural History in New York City. "It's incredible to think," he says.

Whether or not this is true might become clear once scientists spot Laonastes in the wild, which they have yet to do. They suspect it is a reclusive, nocturnal animal that lives in rocky terrain.

Family tree

Evolutionary biologists also want to analyse the Kha-nyou's DNA, to work out where it fits on the rodents' family tree. Such a study could help reveal how different lineages of rodents split in the past and spread around the world.

Researchers now recognize that tropical Southeast Asia, where Laonastes was discovered, contains many previously undocumented plants, insects and larger animals. The new discovery strengthens the argument for the area's uniqueness and the need to conserve it, Dawson says.

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