New Asian Rodent Found as Food Is "Living Fossil," Gene Study Confirms

Mason Inman
for National Geographic News
April 24, 2007
Locals call it the kha-nyou and enjoy it roasted on a skewer.

But when scientists spotted the squirrel-like rodent at a Laotian food market two years ago, they called it a species previously unknown to science.

Now new DNA analysis confirms that the Laotian rock rat is a "living fossil" that belongs to a family of rodents thought to have gone extinct 11 million years ago.

Researchers at first believed the rare Asian species was the only representative of an entirely new family of rodents.

Instead the rock rat is part of a family that split from the rest of the more than 1,500 species of modern-day rodents about 44 million years ago, the new gene study says.

"It's not exactly a fossil," lead study author Dorothée Huchon of Israel's Tel Aviv University, said of the rock rat. "It hasn't stopped evolving."

Rodent Family Tree

Despite its name, the rock rat belongs a rodent group that includes guinea pigs and porcupines and is not as closely related to rats as it is to those animals.

The species is distinguished by its black coat, bushy tail, and ducklike waddle.

The rock rat's closest living relative is the gundi, a rodent found only in Africa with a guinea piglike body and a ratlike head.

The new genetic study bolsters a previous study of fossil rodents published last year in the journal Science.

The new report appears this week in the online edition of the Proceedings of the National Academy of Sciences.

Together, the two data sets finally pin down where the species falls on the rodent family tree, the authors of the new study say.

Working independently on separate genetic tests, three research teams in France, Israel, and the United States compared rock rat genes with the counterpart genes in other rodents.

The scientists looked to see if the rock rat shared genetic mutations with other rodent species, which would suggest a close evolutionary relationship.

"Jumping Genes"

Also for the new study, German researchers examined other pieces of DNA known as transposons, or "jumping genes."

The genes—which copy themselves, float to other spots in the genome, and randomly insert themselves—told the same story about the rock rat's ancient lineage.

"Their result looks pretty solid," said Ronald DeBry, a molecular biologist at the University of Cincinnati in Ohio who was not involved in the research.

He added that by studying the rodent's jumping genes, the study authors "provide a really important and very convincing independent confirmation" of how the various rodent species are related.

Researchers behind the new study argue that, given the rock rat's unusual lineage, it is important to protect the species.

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