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 Luzon (; ) is the largest and most populous island in the Philippines. Located in the northern portion of the Philippines archipelago, it is the economic and political center of the nation, being home to the country's capital city, Manila, as ...

in the

Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...

. They look a great deal like

shrew Shrews (family Soricidae) are small mole-like mammals classified in the order Eulipotyphla. True shrews are not to be confused with treeshrews, otter shrews, elephant shrews, West Indies shrews, or marsupial shrews, which belong to differ ...

s and are an example of

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...

. Shrewlike rats evolved to be vermivores (

worm Worms are many different distantly related bilateral animals that typically have a long cylindrical tube-like body, no limbs, and no eyes (though not always). Worms vary in size from microscopic to over in length for marine polychaete wo ...

-eaters) and insectivores feeding on soft-bodied

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

s associated with

leaf litter Plant litter (also leaf litter, tree litter, soil litter, litterfall or duff) is dead plant material (such as leaves, bark, needles, twigs, and cladodes) that have fallen to the ground. This detritus or dead organic material and its constituent ...

Characteristics

The snout and

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ships * Ros ...

are very long. Eyes are small. Head and body is 18.8–21.5 cm with a tail 10.5–14.6 cm. Only two molars are present on each side of the upper and lower jaws; these are small and peg-like.

Incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...

s are described as needle-like and

mandible In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

s as delicate. Their characteristic method of locomotion has given rise to the epithet "hopping rats," describing their method of pouncing on an earthworm prey before it can slide back into its hole.

Distribution

Shrewlike rats are found at elevations of 1,100 to 2,460 meters. They are restricted to moist, mossy highland regions with ample rainfall and large populations of

earthworm An earthworm is a terrestrial invertebrate that belongs to the phylum Annelida. They exhibit a tube-within-a-tube body plan; they are externally segmented with corresponding internal segmentation; and they usually have setae on all segments. T ...

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

sky island Sky islands are isolated mountains surrounded by radically different lowland environments. The term originally referred to those found on the Mexican Plateau, and has extended to similarly isolated high-elevation forests. The isolation has s ...

s" of Luzon. Specimens have been collected from Mt. Bali-it and Mt. Data of the Central Cordillera (''R. soricoides''), Mt. Tapulao of the

Zambales Mountains The Zambales Mountains is a mountain range 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 Cabusilan Mountain Range composed of Mount ...

(''R. tapulao''), Mount Banahao (''R. banahao''),

Mount Isarog Mount Isarog is an active stratovolcano located in the province of Camarines Sur, Philippines, on the island of Luzon. The mountain has active fumaroles and hot springs. It has an elevation of above mean sea level. The broad isthmus between Lag ...

(''R. isarogensis''), Mt. Labo of the

Bicol Peninsula Bicol, known formally as the Bicol Region or colloquially as Bicolandia ( bcl, Rehiyon kan Bikol; Rinconada Bikol: ''Rehiyon ka Bikol''; Waray Sorsogon, Masbateño: ''Rehiyon san Bikol''; tl, Rehiyon ng Bikol), is an administrative region of ...

(''R. labo'') and Mt. Mingan of the

Sierra Madre Sierra Madre (Spanish, 'mother mountain range') may refer to: Places and mountains Mexico *Sierra Madre Occidental, a mountain range in northwestern Mexico and southern Arizona *Sierra Madre Oriental, a mountain range in northeastern Mexico *S ...

(''R. mingan'').

Relationships

''Rhynchomys'' is an old endemic of the Philippines. The genus is distinct enough to give it its own group distinct from all other old endemics. It was classified as part of the ''Chrotomys'' division along with '' Apomys'', ''

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. An apparently smaller relatives of the true shrew-rats ''Chrotomys'' and '' Rhynchomys'', ''Archbo ...

'', and '' Chrotomys''. Within this division, ''Rhynchomys'' is most closely related to the other Philippine shrew-rats in the genera ''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 2007, two species, ''R. banahao'' and ''R. tapulao'', were described from Mt. Banahao and Mt. Tapulao, respectively. In 2019, two additional species were described, ''R. labo'' and ''R. mingan'' from Mt. Labo and Mt. Mingan, respectively. * Banahao shrew-rat (''Rhynchomys banahao'') Balete ''et al.'', 2007 * Isarog shrew-rat, (''Rhynchomys isarogensis'') Musser and Freeman, 1981 * Labo shrew-rat (''Rhynchomys labo'') Rickart ''et al.'', 2019 * Mingan shrew-rat (''Rhynchomys mingan'') Rickart ''et al.'', 2019 * Mount Data shrew-rat (''Rhynchomys soricoides'') Thomas, 1895 * Tapulao shrew-rat (''Rhynchomys tapulao'') Balete ''et al.'', 2007

References

{{Taxonbar, from=Q1189626 Rats of Asia Rhynchomys Endemic fauna of the Philippines Fauna of Luzon Rodents of the Philippines Taxa named by Oldfield Thomas