Laotian rodent takes scientists by surprise

WASHINGTON — It was thought to have gone extinct 11 million years ago — a chipmunk-sized, brush-tailed rodent with a long head and quick paws well-suited for scooting across the rock escarpments of ancient China and Pakistan.

Then last year in central Laos, western scientists spotted an unusual animal carcass in a meat market near the Mekong River. So unusual, in fact, that it turned out to represent a new rodent family — the first new mammal family to be announced in 30 years. The researchers called it Laonastes aenigmamus, the Laotian "rock rat." Local people call it "kha-nyou."

It turned out that the kha-nyou is a textbook example of a phenomenon known as the "Lazarus effect." A creature, thought to have died out deep in the prehistoric past, suddenly reappears. The kha-nyou, researchers said Thursday, is a modern member of an ancient rodent family last seen as an 11-million-year-old fossil that paleobiologists call Diatomys shantungensis.

"Laonastes didn't rise from the dead," said Mary Dawson, a paleontologist at the Carnegie Museum of Natural History. "You're doing the research, and then you find a gap in the fossil record." What happened to Diatomys between 11 million years ago and now is unknown.

The Lazarus effect has been observed before, most notably with the re-emergence in the Indian Ocean in 1938 of the coelacanth, a fish believed to have gone extinct 65 million years ago.

But the phenomenon is extremely rare among mammals, said Dawson, lead author of an article in today's issue of the journal Science that links the modern-day kha-nyou with the Diatomys of yore.

"I had heard about a paper describing a new family of rodents, which is a real surprise," Dawson said. "When we saw the illustrations, we knew it was a living diatomid."

Researchers then set out to prove that through meticulous comparisons between the bones of today's specimens and fossils found in Asia.

Dawson said the kha-nyou is not exactly the same animal as its ancestor, but it exemplifies the evolutionary uncertainties that prompted University of Chicago paleobiologist David Jablonski in the 1980s to come up with the concept of the Lazarus effect as a cautionary tool in evaluating the fossil record.

"You may not have an extinction," Jablonski said. "You're just missing a lot of information."

What was perhaps not unusual about the kha-nyou was its presence in central Laos. After a half-century of war and isolation, Southeast Asia in the past decade has emerged as a zoological treasure trove, with large swaths of rain forest, mountains and river valley compressed into a relatively small space that few scientists have surveyed.

Naturalists, braving the minefields of Cambodia and the unexploded ordnance of Vietnam and Laos' Ho Chi Minh trail, have in the past several years documented several "new" mammals besides the kha-nyou, including a striped rabbit and a 200-pound oxlike animal called a saola.

Material from The Associated Press is included in this report