Laotian Rock Rat
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[Photo] Laotian Rock Rat (Laonastes aenigmamus) http://www.nytimes.com/imagepages/2005/05/12/international/12rodent_CA0ready.html Copyright 2005, R.J. Timmins. Published in The New York Times.

The Laotian rock rat or kha-nyou (Laonastes aenigmamus), sometimes called the "rat-squirrel", is a rodent species of the Khammouan region of Laos. The species was first described in a 2005 article by Paulina Jenkins and coauthors, who considered the animal to be so distinct from all living rodents that they placed it in a new family, Laonastidae.

In 2006 the classification of the Laotian rock rat was disputed by Mary Dawson and coauthors. The argument was that it belongs to the ancient fossil family Diatomyidae, that was thought to be extinct for 11 million years, or since the late Miocene. It would thereby represent a Lazarus taxon. The animals resemble large dark rats with hairy, thick tails like those on a squirrel. Their skulls are very distinctive and have features that separate them from all other living mammals.

A new family or a Lazarus taxon?
Upon their initial discovery, Jenkins and coauthors (2005) considered the Laotian rock rat to represent a completely new family. The discovery of a new species of an extant mammal genus happens periodically, such as with the leaf muntjac or saola. The discovery of a completely new family is, by comparison, much more unusual. The most recent incident prior to the discovery of the family Laonastidae of the Laotian rock rat by Western science was the discovery of the bumblebee bat (Craseonycteris thonglongyai; family Craseonycteridae) in 1974. The only other examples from the 1900s are represented by species that are only considered distinct families by a few authorities. These discoveries are: the Chinese River Dolphin (Lipotes vexillifer; family Lipotidae) in 1918, the Zagros mouse-like hamster (Calomyscus bailwardi; family Calomyscidae) in 1905, and Goeldi's marmoset (Callimico goeldii; family Callimiconidae) in 1904. Kalinowski's opossum (Hyladelphys kalinowskii), described only in 1992, is currently assigned to the family Didelphidae, but it may represent its own family. Representatives from all the remaining mammal families with living representatives (approximately 30) were discovered prior to 1900.

Jenkins (2004) did not compare the specimens to known rodent fossils. After such a comparison, Dawson et al. (2006) determined that the Laotian rock rat belongs to a previously described family, one which had only been known from fossils, the Diatomyidae. The Diatomyidae are known from a series of fossils from the early Oligocene (~32.5 Ma) until the Miocene (~11 Ma). The discovery of the Laotian rock rat means that an 11 million year gap exists in the fossil record where no diatomyids have been found. Dawson et al. (2006) described the Diatomyidae as a Lazarus taxon due to this gap. The only other comparable length of time for a mammal Lazarus taxon is the monito del monte, which is part of a family (Microbiotheriidae) also most recently known from Miocene deposits. Mary Dawson described Laonastes as the "coelacanth of rodents".[1][2]

Etymology
The genus name for this animal, Laonastes, means "inhabitant of stone" (from Greek λαα?? = laas = stone, gen: λαο?? = laos = of stone and Greek ναστη?? = nastes = inhabitant). This is in reference to its presence around limestone rocks and also to the country where it was recently discovered. The specific epithet aenigmamus means "enigma mouse" (from Greek αινιγμα = ænigma and μυ?? = mus, "mouse") referring to its unknown position among the rodents (Jenkins et al., 2004).

Discovery
The first specimens were found for sale as meat at a market in Thakhek, Khammouan in 1996. Remains of three additional animals were obtained in 1998 from villagers and in an owl pellet. Interestingly, the researchers also obtained two additional rodent species and one insectivore on that expedition that were unknown to science. Scientists were, however, able to assign these animals to known genera (one rodent to Leopoldamys, and the insectivore to Hylomys) or a known subfamily (as in the case of Saxatilomys in the rodent subfamily Murinae).

Return trips to Laos by Wildlife Conservation Society researchers have uncovered several other specimens.[3] These new discoveries have prompted the suggestion that the animals may not be as rare as once thought.

On June 13, 2006, David Redfield, a professor emeritus of Florida State University, and Thai wildlife biologist Uthai Treesucon announced that they had captured, photographed and videotaped a live specimen of the species in the village of Doy in Laos.[4]

Description
The animals look like rats with thick, furred tails. They are about 26 cm long with a 14 cm tail and weigh about 400 g. Jenkins et al. (2004) described the jaw as hystricognathous, but Dawson et al. (2006) argued it is sciurognathous. The infraorbital foramen is enlarged, consistent with a hystricomorphous zygomasseteric system. The pterygoid fossa do not connect to the orbit, setting them apart from the hystricognathous rodents.

Natural history
Laotian rock rats are found in regions of karst limestone. They appear to be found only among limestone boulders on hillsides. Villagers in the area are familiar with the animal, calling it kha-nyou, and trapping it for food. The animals are presumed to be nocturnal.

These rock rats appear to be predominantly herbivores, eating leaves, grass and seeds. They may eat insects as well, but probably not in high abundance. Females may give birth to a single young.

Laotian rock rats appear to be quite docile and slow moving over open ground. They walk with feet splayed outward in a gait that has been described as duck-like. Although not ideal for mobility on open surfaces, this appears to be efficient when scrambling up and across large rocks, the sideways angle allowing for greater surface area for feet to find purchase on an angled surface.

Trivia
The rat-squirrel is the mascot of the City, State and Nation section of The Maneater, the official student newspaper of the University of Missouri-Columbia. The writers in the section recently purchased t-shirts featuring a drawing of the rat-squirrel reading a copy of The Maneater.

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