Earless Water Rat
Encyclopedia
The Earless Water Rat is a New Guinea
rodent
, part of the Hydromys
group of the subfamily of Old World rats and mice (Murinae). It is the only species of the genus Crossomys. This species is probably most closely related to Baiyankamys. It is still unclear to which species this group is related. It is one of the most aquatically adapted rodents of the world.
, based on a single specimen caught by one Mr. C. A. W. Monckton, after whom the species was named, near Brown River
, Central Province, south-east Papua New Guinea
. Only in July 1950 a second specimen was captured. Since then, several other examples have been caught in the mountains of eastern New Guinea, but the Earless Water Rat remains a rather rare species. The scientific name means "Monckton's fringed mouse", which refers to the collector of the original specimen (C. A. W. Monckton) and to the fringe of hairs on the tail.
, but that has not been accepted generally. Lidicker (1968), who studies the morphology of the phallus
of New Guinea rodents, speculated that Crossomys might not be as closely related to Hydromys as was then generally thought. Later on, this was supported by the immunological study of Watts & Baverstock (1994). This study placed Crossomys closer to Leptomys
, Pseudohydromys
and Xeromys than to Hydromys.
The American mammalogists Guy Musser and Michael Carleton, in their contribution to the authoritative Mammal Species of the World (3rd ed.), divided the group of murine rodents that had before been called "Hydromyinae" or "Hydromyini" in two "divisions": the Xeromys Division (Leptomys, Pseudohydromys and Xeromys) and the Hydromys Division (Crossomys, Hydromys, Microhydromys
, Paraleptomys
and Parahydromys[ Baiyankamys was added later]). According to them, the morphology of Crossomys is more like the Hydromys Division than the Xeromys Division, and therefore they placed it in the Hydromys group. They supported their opinion with an unpublished study of the Australian biologist Ken Aplin, who also placed Crossomys closer to Hydromys.
Helgen (2005) concluded that Crossomys is most closely related to Baiyankamys, which had usually been placed in Hydromys before. Baiyankamys has not been studied genetically. According to his data, the Crossomys-Baiyankamys group is most closely related to Hydromys and Parahydromys, though he did not give material to support his opinion.
.
The back is greyish brown, and the belly is white. The fur is soft and water-proof. The top half of the tail is light grey, and the bottom half is white. The forefeet and claws are very small, but the hindfeet are very large. The upper lip contains a row of short, strong brushes, which may be used for rasping. The external ear (the pinna) is reduced to a small oval that does not or hardly protract above the fur. It is possible that the ear canal can be closed. The brain is rather large, like in many aquatic animals. The nasals are relatively small, just like the palate
and the molars. The bulla
e are small. The rostrum
is narrow. The Earless Water Rat is a medium-sized rat, about as large as its close relative Baiyankamys. The head-body length is 175 to 200 mm (6.9 - 7.9 inch) (based on four specimens), tail length is 212 to 260 mm (8.3 - 10.2 inch) (4), hind foot length is 44 to 53 mm (1.7 - 2.1 inch) (4), ear length is 1 to 4,5 mm (0.2 - 7.9 inch) (2), and weight 165 g (5.8 ounce avoirdupois) (1). Females have 0+2=4 mammae (no thoracic and two inguinal
pairs), the same number as most other Australasian rodents.
The Earless Water Rat and Baiyankamys are related because they share the following characters: tail much longer than head-body length; soft, thick, greyish dorsal coat; long, narrow rostrum with a narrow top; very narrow canines; very narrow mesopterygoid fossae; narrow zygomatic arch
es with a high squamosal root. B. habbema also has the reduced external ears of the Earless Water Rat.
This animal lives at 1000 to 2700 meters in elevation in the Central Cordillera of Papua New Guinea
, including the Huon peninsula
. The cold, fast-flowing streams of the mountains are its habitat.
At night it sleeps in holes at the river bank, but at day it is active and hunting for tadpoles, worms and river insects (mostly larvae). The animal gets only one young at the same time. It is only captured by Telefol
hunters when river levels are low.
It is called kwypep by the Kalam tribe (Madang Province
), possibly ogoyam in the Telefol language
(in Sandaun Province
) and momo by the Rofaifo (Southern Highlands Province), although that name is also used for other water rats, like the common Rakali. Some local names can be translated as "water sugar glider
", which refers to the similarity of the fur of these two species.
Little is known about the conservation status of this species, although it has the status "least concern" in the IUCN Red List.
New Guinea
New Guinea is the world's second largest island, after Greenland, covering a land area of 786,000 km2. Located in the southwest Pacific Ocean, it lies geographically to the east of the Malay Archipelago, with which it is sometimes included as part of a greater Indo-Australian Archipelago...
rodent
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
, part of the Hydromys
Hydromys
Hydromys is a genus of rodents in the subfamily Murinae.- List of species :Genus Hydromys - water rats*Rakali, Hydromys chrysogaster E...
group of the subfamily of Old World rats and mice (Murinae). It is the only species of the genus Crossomys. This species is probably most closely related to Baiyankamys. It is still unclear to which species this group is related. It is one of the most aquatically adapted rodents of the world.
History of discovery
This animal was first described in 1907 by the British mammalogist Oldfield ThomasOldfield Thomas
Oldfield Thomas FRS was a British zoologist.Thomas worked at the Natural History Museum on mammals, describing about 2,000 new species and sub-species for the first time. He was appointed to the Museum Secretary's office in 1876, transferring to the Zoological Department in 1878...
, based on a single specimen caught by one Mr. C. A. W. Monckton, after whom the species was named, near Brown River
Brown River
The Brown River is a short river of New Zealand. It flows northwest to meet the Poerua River five kilometres southeast of Lake Brunner....
, Central Province, south-east Papua New Guinea
Papua New Guinea
Papua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands...
. Only in July 1950 a second specimen was captured. Since then, several other examples have been caught in the mountains of eastern New Guinea, but the Earless Water Rat remains a rather rare species. The scientific name means "Monckton's fringed mouse", which refers to the collector of the original specimen (C. A. W. Monckton) and to the fringe of hairs on the tail.
Relationships
The German mammalogist Hans Rümmler placed this rodent (and Parahydromys asper) in HydromysHydromys
Hydromys is a genus of rodents in the subfamily Murinae.- List of species :Genus Hydromys - water rats*Rakali, Hydromys chrysogaster E...
, but that has not been accepted generally. Lidicker (1968), who studies the morphology of the phallus
Phallus
A phallus is an erect penis, a penis-shaped object such as a dildo, or a mimetic image of an erect penis. Any object that symbolically resembles a penis may also be referred to as a phallus; however, such objects are more often referred to as being phallic...
of New Guinea rodents, speculated that Crossomys might not be as closely related to Hydromys as was then generally thought. Later on, this was supported by the immunological study of Watts & Baverstock (1994). This study placed Crossomys closer to Leptomys
Leptomys
Leptomys is a genus of rodent from New Guinea. It is considered part of the New Guinea Old Endemics, meaning it was part of the first wave of murine rodents to colonize the island.-Species:* Leptomys arfakensis Musser, Helgen & Lunde, 2008...
, Pseudohydromys
Pseudohydromys
Pseudohydromys is a genus of rodent in the family Muridae.It contains the following species:* Bishop moss-mouse * Huon small-toothed moss-mouse...
and Xeromys than to Hydromys.
The American mammalogists Guy Musser and Michael Carleton, in their contribution to the authoritative Mammal Species of the World (3rd ed.), divided the group of murine rodents that had before been called "Hydromyinae" or "Hydromyini" in two "divisions": the Xeromys Division (Leptomys, Pseudohydromys and Xeromys) and the Hydromys Division (Crossomys, Hydromys, Microhydromys
Microhydromys
Microhydromys is a genus of rodent in the family Muridae.It contains the following species:* Southern groove-toothed moss-mouse * Northern Groove-toothed Shrew Mouse...
, Paraleptomys
Paraleptomys
Paraleptomys is a genus of rodent from New Guinea. It is considered part of the New Guinea Old Endemics, meaning it was part of the first wave of murine rodents to colonize the island.-Species:*Genus Paraleptomys...
and Parahydromys
Helgen (2005) concluded that Crossomys is most closely related to Baiyankamys, which had usually been placed in Hydromys before. Baiyankamys has not been studied genetically. According to his data, the Crossomys-Baiyankamys group is most closely related to Hydromys and Parahydromys, though he did not give material to support his opinion.
Characteristics
Of all muroids, the Earless Water Rat is adapted best to a life in water. It has extremely long hindfeet, the toes of which are webbed completely, strongly reduced forelegs, absent or invisible ears, very small eyes, and a long tail with a row of hairs at the downside. That row starts at each side of the beginning of the tail as a long white row of hairs; these two rows merge together at about 50 mm from the beginning of the tail and the row goes on to the end of the tail. In all these characters, it resembles the Web-footed Water Shrew (Nectogale elegans), a good example of convergent evolutionConvergent 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...
.
The back is greyish brown, and the belly is white. The fur is soft and water-proof. The top half of the tail is light grey, and the bottom half is white. The forefeet and claws are very small, but the hindfeet are very large. The upper lip contains a row of short, strong brushes, which may be used for rasping. The external ear (the pinna) is reduced to a small oval that does not or hardly protract above the fur. It is possible that the ear canal can be closed. The brain is rather large, like in many aquatic animals. The nasals are relatively small, just like the palate
Palate
The palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior...
and the molars. The bulla
Bulla
-People:* Anton Bulla, a Slovak footballer and coach* Clyde Robert Bulla , an American author of books for children* Johnny Bulla, an American golfer* Karl Bulla, a Russian photographer* Max Bulla, an Australian bicycle racer...
e are small. The 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....
is narrow. The Earless Water Rat is a medium-sized rat, about as large as its close relative Baiyankamys. The head-body length is 175 to 200 mm (6.9 - 7.9 inch) (based on four specimens), tail length is 212 to 260 mm (8.3 - 10.2 inch) (4), hind foot length is 44 to 53 mm (1.7 - 2.1 inch) (4), ear length is 1 to 4,5 mm (0.2 - 7.9 inch) (2), and weight 165 g (5.8 ounce avoirdupois) (1). Females have 0+2=4 mammae (no thoracic and two inguinal
Inguinal
In human anatomy, the inguinal region refers to either the groin or the lower lateral regions of the abdomen. It may also refer to:* Conjoint tendon, previously known as the inguinal aponeurotic falx, a structure formed from the transversus abdominis insertion into the pecten pubis* Granuloma...
pairs), the same number as most other Australasian rodents.
The Earless Water Rat and Baiyankamys are related because they share the following characters: tail much longer than head-body length; soft, thick, greyish dorsal coat; long, narrow rostrum with a narrow top; very narrow canines; very narrow mesopterygoid fossae; narrow zygomatic arch
Zygomatic arch
The zygomatic arch or cheek bone is formed by the zygomatic process of temporal bone and the temporal process of the zygomatic bone , the two being united by an oblique suture; the tendon of the Temporalis passes medial to the arch to gain insertion into the coronoid process...
es with a high squamosal root. B. habbema also has the reduced external ears of the Earless Water Rat.
Distribution, habitat and behavior
Papua New Guinea
Papua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands...
, including the Huon peninsula
Huon Peninsula
Huon Peninsula is a large rugged peninsula on the island of New Guinea in Morobe Province, eastern Papua New Guinea. It is named after French explorer Jean-Michel Huon de Kermadec who discovered it along with his personal assistant and porter, Henry Ole. The peninsula is dominated by the steep...
. The cold, fast-flowing streams of the mountains are its habitat.
At night it sleeps in holes at the river bank, but at day it is active and hunting for tadpoles, worms and river insects (mostly larvae). The animal gets only one young at the same time. It is only captured by Telefol
Telefol people
-History:Telefol history starts with the "Old Woman" traveling through the land that is now the Eliptaman valley. She, as told through their creation stories, founded the Telefolip, the most sacred of Yolam Houses or Haus Tambaran in the Star Mountains Region about 300 years ago...
hunters when river levels are low.
It is called kwypep by the Kalam tribe (Madang Province
Madang Province
Madang is a province on the northern coast of mainland Papua New Guinea. The province has many of the country's highest peaks, active volcanoes and its biggest mix of languages...
), possibly ogoyam in the Telefol language
Telefol language
Telefol is a language spoken by the Telefol people in Papua New Guinea, notable for possessing a base-27 numeral system.-History:The Iligimin people also spoke Telefol, but they were defeated by the Telefol proper.-Orthography:...
(in Sandaun Province
Sandaun
Sandaun Province, officially West Sepik Province, is the north-westernmost province of Papua New Guinea. It covers an area of 36,300 km² and has a population of 185,741 . The capital is Vanimo...
) and momo by the Rofaifo (Southern Highlands Province), although that name is also used for other water rats, like the common Rakali. Some local names can be translated as "water sugar glider
Sugar Glider
The sugar glider is a small gliding possum originating from the marsupial family.The sugar glider is native to eastern and northern mainland Australia and is also native to New Guinea and the Bismarck Archipelago.- Habitat :Sugar gliders can be found all throughout the northern and eastern parts of...
", which refers to the similarity of the fur of these two species.
Little is known about the conservation status of this species, although it has the status "least concern" in the IUCN Red List.