The Laotian rock rat or kha-nyou (Laonastes aenigmamus, Lao: ຂະຍຸ), 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. 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. After such a comparison, Dawson et al. believed the Laotian rock rat belongs to a previously described family, which had only been known from fossils, the Diatomyidae, so not a new family at all, but simply one that had been believed extinct. The Diatomyidae are known from a series of fossils from the early Oligocene (~32.5 mya) until the Miocene (~11 mya). The discovery of the Laotian rock rat means an 11 million-year gap exists in the fossil record where no diatomyids have been found. Dawson et al. described the