Leigh Kish, Media Relations Manager
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Pittsburgh, PA, 15213
For Immediate Release
Contact: Leigh Kish 412.622.3361
March 9, 2006
Embargoed: Not for Release Until
family of mammal really living fossil
Pittsburgh … Laonastes aenigmamus, a rodent first described in 2005, made international headlines as the sole member of a new family of mammals. But according to a paper published today in Science, the animal is actually a surviving member of the rodent family Diatomyidae, thought to be extinct for 11 million years.
A team of international researchers, led by Carnegie Museum of Natural History Curator Emerita of Vertebrate Paleontology Mary Dawson, PhD, claims it's a living fossil and a particularly striking example of the "Lazarus effect" in mammals.
[The "Lazarus effect" is when a taxon thought to be extinct is rediscovered after a temporal gap. An example is the Coelacanth. The coelacanth was believed to have been extinct since the end of the Cretaceous period approximately 135 - 65 million years ago. A live specimen was caught by fishermen off the east coast of South Africa in 1938. With the exception of a South American marsupial, all fossil mammal taxa that were subsequently found alive have been Pleistocene in age (1.9 million - 10,000 years ago.]
"It is an amazing discovery and it's the coelacanth of rodents," said Dawson. "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. That's quite a gap. Previous mammals had a gap of only a few thousand to just over a million years."
Laonastes was found for sale as meat in a market in the Khammouan region of Laos in 1996 and described as a new family of mammal in 2005. No Western scientists have observed a specimen alive. But when Dawson and her colleague Carnegie Museum of Natural History Curator of Vertebrate Paleontology Chris Beard, PhD, downloaded the paper, they recognized the animal immediately.
"We knew exactly what we were looking at," said Beard. "The teeth were the most telling sign. We were sure we were looking at living Diatomyidae."
Diatomyidae are rodents that lived during the middle Tertiary (34 - 11 million years ago) in southern Asia, central China, and Japan. They were rodents of medium size and highly characteristic molar teeth and jaw structure. Three known fossil genera- Fallomus, Diatomys, and Willmus- are recognized in the Diatomyidae. Some fossils are known from isolated teeth and jaw fragments. Others such as Diatomys are better known and more widely distributed.
In addition to the excitement of finding a thought be extinct relative of a Diatomyidae, the scientists were also able to make certain morphological predictions about Laonastes based on the fossils already described. And their predictions were very accurate.
"One of the beautiful parts of this discovery was that we ( Beard, Gregoire Metais also of Carnegie Museum of Natural History, and Dawson) were able to correctly predict that Laonastes would have four roots in its molars just as in Diatomys and Fallomus and multiserial microscopic structure of the enamel of the incisors," said Dawson. "The enamel is an very important feature used by scientists studying rodent evolution."
As the scientists were checking the fossil record and making arrangements to study Laonastes, a new specimen of Diatomys was found by Chuan Kui Li, the colleague who first described it in 1974. This new specimen provided morphological information showing remarkable similarities to the living Laonastes.
These similarities included structural details of the skull, lower jaw, and even the size of the animal. The teeth of Laonastes are more highly evolved than Diatomys but have a similar basic pattern. The excitement of finding a living relative is tempered by that fact there are not any plans in place to protect and conserve Laonastes and other unique organisms recently found in Southeast Asia.
"It's the sole survivor of a very distinctive family of rodents with deep evolutionary roots in Asia," said Beard. "Every effort should be made to protect and preserve the living Laonastes."
"Laonastes is not the only new organism to be discovered in southeastern Asia," said Dawson. "Other new mammals, plants, reptiles discovered in recent years in this part of the world have greatly augmented our understanding of biodiversity. The highest priority must be given to preserving this unique biota and especially Laonastes while it is still possible."
Laonastes also adds to the recent groundbreaking theories that many mammals originated in Asia and later dispersed from there to Africa and the Western Hemisphere. Laonastes' closest living relative is the gundis of Africa.
Contact Leigh Kish for available images.