Tuesday, December 25, 2012

[Mammalogy • 2007] Laonastes aenigmamus | Kha-nyou | Laotian Rock Rat • Multiple molecular evidences for a living mammalian fossil

Fig. 1. A juvenile Laonastes aenigmamus, captured and released after photography, provides evidence that this species is, indeed, very much alive. Known locally as Kha-nyou, the Laotian rock rat possesses a rat-like head with long whiskers and a furry squirrel-like tail. It lives in the limestone rock outcroppings of central Lao People's Democratic Republic. (Photo by Uthai Treesucon, David Redfield 2006 Lao expedition).
doi: 10.1073/pnas.0701289104 

Abstract Laonastes aenigmamus is an enigmatic rodent first described in 2005. Molecular and morphological data suggested that it is the sole representative of a new mammalian family, the Laonastidae, and a member of the Hystricognathi. However, the validity of this family is controversial because fossil-based phylogenetic analyses suggest that Laonastes is a surviving member of the Diatomyidae, a family considered to have been extinct for 11 million years. According to these data, Laonastes and Diatomyidae are the sister clade of extant Ctenodactylidae (i.e., gundies) and do not belong to the Hystricognathi. To solve the phylogenetic position of Laonastes, we conducted a large-scale molecular phylogeny of rodents. The analysis includes representatives of all major rodent taxonomic groups and was based on 5.5 kb of sequence data from four nuclear and two mitochondrial genes. To further validate the obtained results, a short interspersed element insertion analysis including 11 informative loci was also performed. Our molecular data based on sequence and short interspersed element analyses unambiguously placed Laonastes as a sister clade of gundies. All alternative hypotheses were significantly rejected based on Shimodaira–Hasegawa tests, supporting the idea that Laonastes does not belong to the Hystricognathi. Molecular dating analysis also supports an ancient divergence, ≈44 Mya ago, between Ctenodactylidae and Laonastes. These combined analyses support the hypothesis that Laonastes is indeed a living fossil. Protection of this surviving species would conserve an ancient mammalian family. 

Keywords: Laonastes aenigmamus, molecular phylogeny, rodent, retroposons

Fig. 3. Molecular time scale for the order Rodentia.

Fig. 4. Phylogenetic affiliations of Laonastes based on presence/absence patterns of retroposed SINEs. The phylogenetic tree indicates the three major rodent clades: the mouse-related clade, the Ctenohystrica, and the squirrel-related clade.

Huchon, D., Chevret, P., Jordan, U., Kilpatrick, C.W., Ranwez, V., et al. 2007. Multiple molecular evidences for a living mammalian fossil. PNAS Proc Natl Acad Sci USA 104 (18): 7495–7499. doi: 10.1073/pnas.0701289104