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Shrewlike rats
Fossil range: Recent
Rhynchomys soricoides (lower animal)
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Muridae
Subfamily: Murinae
Genus: Rhynchomys
Thomas, 1895
Species

Rhynchomys banahao
Rhynchomys isarogensis
Rhynchomys soricoides
Rhynchomys tapulao

Distribution of shrewlike rats on Luzon Island. Orange = R. soricoides, red = R. tapulao, blue = R. banahao, and green = R. isarogensis.

The shrewlike rats, genus Rhynchomys, also known as the tweezer-beaked rats are a group of unusual Old World rats found only on the island of Luzon in the Philippines. They look a great deal like shrews and are an example of convergent evolution. Shrewlike rats evolved to be vermivores (worm-eaters) and insectivores feeding on soft-bodied invertebrates associated with leaf litter.

Contents

Characteristics

The snout and rostrum are very long. Eyes are small. Head and body is 18.8-21.5 cm with a tail 10.5-14.6 cm (Nowak, 1999). Only two molars are present; these are small and peg-like. Incisors are described as needle-like and mandibles as delicate (Nowak, 1999; Balete et al., 2007).

Distribution

Shrewlike rats are found at elevations of 1,100 to 2,460 meters (Nowak, 1999; Balete et al., 2007). They are restricted to moist, mossy highland regions with ample rainfall and large populations of earthworms. Populations appear to be very isolated, restricted to "sky islands" of Luzon. Specimens have been collected from Mount Bali-it and Mount Data of the Central Cordillera (R. soricoides), Mount Tapulao of the Zambales Mountains (R. tapulao), Mount Banahao (R. banahao), and Mount Isarog (R. isarogensis; Balete et al., 2007).

Relationships

Musser and Heaney (1992) recognized Rhynchomys as an Old Endemic of the Philippines. They considered the genus distinct enough to give it its own group distinct from all other Old Endemics. Musser and Carleton (2005) classified it as part of the Chrotomys Division along with Apomys, Archboldomys, and Chrotomys. Jansa et al. (2006) supported this relationship and determined that within this division, Rhynchomys is most closely related to the other Philippine shrew-rats in the genus Archboldomys and Chrotomys.

Species

From 1895 until 1981, Rhynchomys was only known from a few specimens taken from near the type locality of R. soricoides. In 1981, this was expanded by one species with the discovery and description of R. isarogensis. In April, 2007, Balete and colleagues described two additional species, R. banahao and R. tapulao from Mount Banahao and Mount Tapulao respectively.

References

  • Balete, D. S., E. A. Rickart, R. G. B. Rosell-Ambal, S. Jansa, and L. R. Heaney, 2007. Descriptions of two new species of Rhynchomys Thomas (Rodentia: Muridae: Murinae) from Luzon Island, Philippines. Journal of Mammalogy 88 (2): 287-301.
  • Jansa, S., F. K. Barker, and L. R. Heaney. 2006. The pattern and timing of diversification of Philippine endemic rodents: evidence from mitochondrial and nuclear gene sequences. Systematic Biology, 55:73-88.
  • Musser, G. G. and M. D. Carleton. 2005. Superfamily Muroidea. Pp. 894-1531 in Mammal Species of the World a Taxonomic and Geographic Reference. D. E. Wilson and D. M. Reeder eds. Johns Hopkins University Press, Baltimore.
  • Musser, G. G. and L. R. Heaney. 2006. Philippine rodents: Definitions of Tarsomys and Limnomys plus a preliminary assessment of phylogenetic patterns among native Philippine murines (Murinae, Muridae). Bulletin of the American Museum of Natural History, 211:1–138.
  • Nowak, R.M. 1999. Walker's Mammals of the World, Vol. 2. Johns Hopkins University Press, London.
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