The Laotian rock rat or kha-nyou (Laonastes aenigmamus, ), sometimes called the "rat-squirrel", is a species of rodent found in 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, they placed it in a new family, Laonastidae. It is in the monotypic genus Laonastes.

thumb|Skull of L. aenigmamus

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

Classification

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, or a new genus, happens periodically, such as with the leaf muntjac or the saola. The discovery of a completely new family is, by comparison, much more unusual. The most recent comparable incident before this discovery by Western science was the discovery of the bumblebee bat (Craseonycteris thonglongyai; family Craseonycteridae) in 1974. The only other examples from the 20th century are 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. Representatives from all the remaining rodent families with living representatives (approximately 30) were discovered before 1900.

Jenkins et al. did not compare the specimens to known rodent fossils.

The analysis of mtDNA 12S rRNA and cytochrome b sequence by Jenkins et al. allied Laonastes with African hystricognath rodents, namely the blesmols and the dassie rat. Remains of three additional animals were obtained in 1998 from villagers and in an owl pellet. Return trips to Laos by the Wildlife Conservation Society researchers uncovered several other specimens.

Description

The animals look generally like rats, with thick, furred tails similar to a squirrel's, but limp. The head is large, with round ears and a somewhat bulbous bridge of the nose, and very long whiskers. Their fur is dark slate grey, with a blackish tail. The belly is lighter, with a small, whitish area in the center. Their eyes are beady and black. They are about long with a tail and weigh about . Jenkins et al. (2004) described the jaw as hystricognathous, but Dawson et al. argued it is sciurognathous. The infraorbital foramen is enlarged, consistent with a hystricomorphous zygomasseteric system. The pterygoid fossae do not connect to the orbit, setting them apart from the hystricognathous rodents. In Vietnam, it is found in the 5 communes (xã) of Thượng Hoá, Hóa Sơn, Trung Hoá, Hóa Hợp, and Dân Hoá, and in Phong Nha – Kẻ Bàng National Park, near the villages of the Vietic-speaking Ruc, Sach, and Chut ethnic groups. It is also found directly across the border in Hin Namno National Biodiversity Conservation Area, Laos. In Laos, it is most common in the Phou Hin Poun National Biodiversity Conservation Area. Nguyen et al.

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.

Further reading

  • Wilson, D. E. & Reeder, D. M. (1993): Mammal Species of the World: A Taxonomic and Geographic Reference. Washington D.C., Smithsonian Institution Press.
  • 2006. Une récente découverte au Laos: le Kha-nyou rongeur énigmatique. Le Courrier de la Nature 213:28–33.
  • Laonastes aenigmamus, an enigmatic rodent recently discovered in Laos. Bull. Acad. Vet., France 164, 135–140.
  • 2011. Highly divergent lineages within the recently described rodent species Laonastes aenigmamus. Implications for its conservation. Journal of Mammalogy 92 (3): 620–628.
  • , 2012. Ontogeny of the cranial system in Laonastes aenigmamus. J. Anat. 221:128–137
  • "Oddball Rodent" Found (in Plain View) Is Called New to Science
  • Carnegie Museum Press Release: "New family of mammal really living fossil" with images
  • Environment News Service: "Rodent Discovered in Laos Defines New Family of Mammals" contains photos
  • Retired Professor Captures A 'Living Fossil' – Laotian Rock Rat Once Believed To Have Gone Extinct Florida State University (ScienceDaily) June 14, 2006
  • Tel Aviv University gene study supports "living fossil" hypothesis