Laotian rock rat, 'rat squirrel' or kha-nyou (Laonastes aenigmamus)
The Laotian rock rat is a rodent from the Khammouan region of Laos. The first specimens were found for sale as meat at a market in Thakhek, Khammouan in 1996. Other remains were obtained from villagers and in an owl pellet in 1998. The species was described in 2005 by Paulina Jenkins and coauthors (1). The authors thought it was so distinct from all living rodents, they put it in a new family, Laonastidae. In 2006, Mary Dawson and coauthors suggested instead it belongs to the fossil family Diatomyidae, which are known from a series of fossils from the early Oligocene (about 32.5 million years ago) to the late Miocene (about 11 million years ago) (3). Jenkins et al. (2) analysed nucleic acid and cytochrome b sequences, which allied Laonastes with African hystricognath rodents, such as blesmols and dassie rats. Huchon et al. (2007) conducted a large-scale molecular phylogeny of rodents, using sequence data from four nuclear and two mitochondrial genes. Their data place Laonastes as a sister clade of the gundis and support a divergence in the Lutetian (Early/Middle Eocene, about 44 million years ago).
The Laotian rock rat resembles a large, dark grey rat with a hairy, thick, blackish tail like that of a squirrel, but limp. The large head has round ears, a bulbous bridge of the nose and very long whiskers. The belly is lighter, with a small, whitish area in the center. Their eyes are beady and black. They are about 26 cm (10 in) long with a 14 cm (5.5 in) tail and weigh about 400 g (14 oz). 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 fossae do not connect to the orbit, setting them apart from the hystricognathous rodents.
The distinctive skull has features unlike those of other living mammals.
References: 1. Jenkins et al. (2005); 2. Jenkins et al. (2004); 3. Dawson et al. (2006); 4. Huchon et al. (2007); 5. "New Pictures of Living Fossil" (2006)