Laotian rock rat
From Biocrawler, the free encyclopedia.
| Laotian rock rat | ||||||||||||||||
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 Laonastes drawing by R.J. Timmins | ||||||||||||||||
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| Laonastes aenigmamus (Jenkins, Kilpatrick, Robinson, Timmins, 2005) |
The kha-nyou or Laotian rock rat (Laonastes aenigmamus) is a rodent from the Khammouan region of Laos. The species was first described in an article issued 18 April, 2005 by Jenkins and colleagues who considered it to be so distinct from all living rodents that they placed it in a new family, Laonastidae. The animals resemble large dark rats with a haired thick tail. Their skulls are very distinct and have features that separate them from all other mammals.
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A new family
The discovery of a new species of extant mammal that represents a completely new family is a rare occurrence. The most recent incident prior to the discovery 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: Chinese river dolphin (Lipotes vexillifer; family Lipotidae) in 1918, Zagros mouse-like hamster (Calomyscus bailwardi; family Calomyscidae) in 1905, and Goeldi's marmoset (Callimico goeldii; family Callimiconidae) in 1904. The 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 (~30) were discovered prior to 1900.
Etymology
The genus name for this animal, Laonastes, means "inhabitant of stone". This is in reference to its presence around limestone rocks. The specific epithet aenigmamus means "enigmatic mouse" referring to its unknown position among the rodents.
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. As of 2005, no Laotian rock rats have been observed alive by Western scientists. Interestingly, the researchers also obtained two additional rodent species on that expedition that were unknown to science. These animals, however, could be assigned to known genera (Niviventer, and Hylomys)
Description
The animals look like rats with furred thick tails. They are about 26 cm long with a 14 cm tail and weigh about 400 g. They have a hystricognathous jaw and an enlarged infraorbital foramen consistent with a hystricomorphous zygomasseteric system. The pterygoid fossa do not connect to the orbit making them unique among the hystricognathous rodents.
Natural history
The Laotian rock rats are found in regions of karst limestone. They appear to be found only among limestone boulders on hillsides. Villagers know the animal, calling it kha-nyou, and trap the rodents for food. The animals are presumed to be nocturnal.
These rock rats appear to be predominantly herbivores, eating leaves, grass and seeds. Insects may be eaten as well, but probably not in high abundance. Females may give birth to a single young.
Relation to other species
The results of the phylogenetic analyses performed by Jenkins et al. (2005) are somewhat inconclusive and contradictory. Both morphology and molecules show Laonastes as a member of the rodent suborder Hystricognathi. The morphological analysis suggests that it is the most basal member of the suborder. This would suggest that this living fossil represents the first living evolutionary split among the hystricognaths. In other words, all living members of the suborder Hystricognathi are more closely related to one another than to the Laotian rock rat.
The molecular analyses suggest that Laonastes is related to the living African hystricognaths such as the dassie rats and the naked mole rat. Another type of analysis on the same data produces the same result as morphology; Laonestes represents the earliest split among hystricognaths. Neither analysis, however, shows more than moderate statistical support for the relationship of Laonastes within the hystricognaths.
References
- Jenkins, P. D., C. W. Kilpatrick, M. F. Robinson, and R. J. Timmins. 2004. Morphological and molecular investigations of a new family, genus and species of rodent (Mammalia: Rodentia: Hystricognatha) from Lao PDR. Systematics and Biodiversity, 2:419-454.
- Wilson, D. E. and D. M. Reeder. 1993. Mammal Species of the World: A Taxonomic and Geographic Reference. Washington D.C., Smithsonian Institution Press.
External links
- Systematics and Biodiversity (http://journals.cambridge.org/bin/bladerunner?REQUNIQ=1113990846&REQSESS=6155349&117000REQEVENT=&REQINT1=292892&REQAUTH=0) Paulina D Jenkins C William Kilpatrick, Mark F Robinson and Robert J Timmins, Morphological and molecular investigations of a new family, genus and species of rodent (Mammalia: Rodentia: Hystricognatha) from Lao PDR, Volume 2, Issue 4 - December 2004
- 'Oddball Rodent' Found (in Plain View) Is Called New to Science (http://www.nytimes.com/2005/05/12/science/12rodent.html?ex=1270785600&en=37bef79604f97228&ei=5090&partner=rssuserland)
- Natural History Museum, London: news article including photos. (http://www.nhm.ac.uk/about-us/news/2005/may/news_4213.html)
- CBC.ca Scientists discover new oddball rodent (http://www.cbc.ca/story/science/national/2005/05/11/Rat050511.html)
- Zoo-talk.com: New species of rodent discovered (http://www.zoo-talk.com/archives/00000307.htm)da:Laonastes aenigmamusla:Laonastes
nl:Laotiaanse rotsrat nn:Laonastes ænigmatus pt:Rato da pedra laotiano
