The shrewlike rats, genus Rhynchomys, also known as the tweezer-beaked rats are a group of unusual Old World rats

Murinae

The Old World rats and mice, part of the subfamily Murinae in the family Muridae, comprise at least 519 species. This subfamily is larger than all mammal families except the Cricetidae and Muridae, and is larger than all mammal orders except the bats and the remainder of the...

 found only on the island of Luzon

Luzon

Luzon is the largest island in the Philippines. It is located in the northernmost region of the archipelago, and is also the name for one of the three primary island groups in the country centered on the Island of Luzon...

 in the Philippines

Philippines

The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...

. They look a great deal like shrew

Shrew

A shrew or shrew mouse is a small molelike mammal classified in the order Soricomorpha. True shrews are also not to be confused with West Indies shrews, treeshrews, otter shrews, or elephant shrews, which belong to different families or orders.Although its external appearance is generally that of...

s and are an example of convergent evolution

Convergent evolution

Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...

. Shrewlike rats evolved to be vermivores (worm

Worm

The term worm refers to an obsolete taxon used by Carolus Linnaeus and Jean-Baptiste Lamarck for all non-arthropod invertebrate animals, and stems from the Old English word wyrm. Currently it is used to describe many different distantly-related animals that typically have a long cylindrical...

-eaters) and insectivore

Insectivore

An insectivore is a type of carnivore with a diet that consists chiefly of insects and similar small creatures. An alternate term is entomophage, which also refers to the human practice of eating insects....

s feeding on soft-bodied

Soft-bodied organisms

The term "soft-bodied organism" is used to describe animals without skeleton, roughly corresponding to the group Vermes as proposed by Carl von Linné. All animals have muscles, but since muscles can only pull, never push, a number of animals have developed hard parts that the muscles can pull on,...

 invertebrate

Invertebrate

An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...

s associated with leaf litter.

Characteristics

The snout and rostrum

Rostrum (anatomy)

The term rostrum is used for a number of unrelated structures in different groups of animals:*In crustaceans, the rostrum is the forward extension of the carapace in front of the eyes....

 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 molar

Molar (tooth)

Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....

s are present; these are small and peg-like. Incisor

Incisor

Incisors are the first kind of tooth in heterodont mammals. They are located in the premaxilla above and mandible below.-Function:...

s are described as needle

Needle

-Crafting:* Knitting needle, a tool for knitting, not as sharp as a sewing needle* Sewing needle, a long slender tool with a pointed tip* Upholstery needle, a tool for upholstery, generally thick and curved-Botany:* Pine needle, the adult leaf of a pine tree...

-like and mandible

Mandible

The mandible pronunciation or inferior maxillary bone forms the lower jaw and holds the lower teeth in place...

s 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 earthworm

Earthworm

Earthworm is the common name for the largest members of Oligochaeta in the phylum Annelida. In classical systems they were placed in the order Opisthopora, on the basis of the male pores opening posterior to the female pores, even though the internal male segments are anterior to the female...

s. Populations appear to be very isolated, restricted to "sky island

Sky island

Sky islands are mountains that are isolated by surrounding lowlands of a dramatically different environment, a situation which, in combination with the altitudinal zonation of ecosystems, has significant implications for natural habitats. Endemism, vertical migration, and relict populations are...

s" 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

Zambales Mountains

The Zambales Mountains is a mountain range located on western Luzon island in the Philippines. The mountains separate Luzon's central plain from the South China Sea. Its most prominent section is known as the Tri-Cabusilan Mountain Range composed of Mt. Pinatubo, Mount Negron and Mount Cuadrado...

 (R. tapulao), Mount Banahao

Mount Banahaw

Mount Banahaw is an active volcano on Luzon Island in the Republic of the Philippines. The three-peaked volcano complex is located between the provinces of Laguna and Quezon and is the tallest mountain in the CALABARZON region dominating the landscape for miles around.The mountain is considered by...

 (R. banahao), and Mount Isarog

Mount Isarog

Mount Isarog is a potentially active stratovolcano located in the province of Camarines Sur, Island of Luzon, Philippines.It was here that Bicolano guerillas hid during the Japanese Period...

 (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

Apomys

Apomys is a genus of rodent endemic to the Philippines. Mice belonging to this genus are generally called Philippine forest mice and can be found on most islands of the Philippines except in Palawan, the Sulu Archipelago, and the Batanes and Babuyan group of islands.Apomys mice weigh from 18g to...

, Archboldomys

Archboldomys

Archboldomys, the shrew-mice, are a genus of rodents in the family Muridae. They are carnivores that feed on invertebrates much like shrews do...

, and Chrotomys

Chrotomys

The genus Chrotomys contain a unique group of rodents found only in the Philippines, specifically the islands of Luzon, Mindoro, and Sibuyan. Instead of being predominantly herbivorous or omnivorous like other murines, these rats feed predominantly on invertebrates although they do eat some...

. 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.

• Rhynchomys banahao Balete, Rickart, Rosell-Ambal, Jansa, & Heaney, 2007
• Isarog Shrewlike Rat, Rhynchomys isarogensis Musser and Freeman, 1981
• Mount Data Shrew Rat - Rhynchomys soricoides Thomas, 1895
• Rhynchomys tapulao Balete, Rickart, Rosell-Ambal, Jansa, & Heaney, 2007