71.
Ethiopian Water Mouse
(Nilopegamys plumbeus)
CR
Overview
Known only from a single specimen, this highly distinctive mouse has more extreme adaptations for swimming than those of any other African murid. These include a large brain, swollen muzzle and extensive vibrissae which may form a sonar system for detecting aquatic invertebrates, reduced and densely furred ears, soft, dense fur for buoyancy, and enlarged hind feet with hairy fringes. Although the feet lack webbing, they are broad enough to be used as paddles for swift, agile swimming. The only known individual of this species was collected in the 1920s. Since then its habitat has been completely destroyed through overgrazing by livestock. Two attempts to find this unique water mouse have failed, leading researchers to fear that it may already be extinct.
Urgent Conservation Actions
Further surveys to determine whether or not this species is extinct.
Distribution
Northwestern Ethiopia

 
Evolutionary Distinctiveness
Order: Rodentia
Family: Muridae
This highly distinctive monotypic rodent can be distinguished from all other African mice by external, cranial, post-cranial and dental characters. It belongs to a guild of “waders” which includes African murids in the genera Colomys, Malacomys, and Deomy. Without swimming and while perched on elongated hind feet, these species consume insects and other small animals in shallow forest streams and pools. While these species exhibit varying degrees of semi-aquatic specializations, Nilopegamys has far more extreme adaptations for swimming, and in this respect more closely resembles the Neotropical ichthyomyines or Australasian hydromyines. Its neurological adaptations to life in water are unique among the African murids, accentuating the distinctiveness of this possibly extinct water mouse.
Description
Size: 
Head and body length: 148 mm
Tail length: 180 mm

Known only from one specimen, this highly distinctive mouse has a thick, soft pelage and large, broad hind feet. Its adaptations for swimming are more extreme than those of any other African murid. The species is superficially similar to the New World “fish-eating rats” although its adaptations for semi-aquatic life are less extreme. It possesses a large brain, swollen muzzle and extensive vibrissae which may form a sonar system for detecting aquatic invertebrates, reduced and densely furred ears, soft, dense fur for buoyancy, and enlarged hind feet with hairy fringes. Although the feet lack webbing, they are broad enough to be used as paddles for swift, agile swimming. The upper parts are dark brown and sharply demarcated from the white underparts. The tail is long and bicoloured.
Ecology
This water-adapted, insectivorous rodent is likely to have occurred at low densities. Little is known of its ecology since it is known from only one specimen.
Habitat
The single known specimen was recorded from highland, riparian habitat. This species represents the most extreme adaptation to an aquatic environment amongst the African Murids.
Distribution
Known only from one specimen trapped near the source of the Little Abbai at Gojjam in northwestern Ethiopia. It was collected at an elevation of 2,600 m asl. Further surveys have been unable to locate this species.
Population Estimate
This species is known from a single specimen, and it may now be extinct. Two attempts have been made to recollect this species, but without any success.
Status
Listed as Critically Endangered (B2ab(iii)) on the 2011 IUCN Red List of Threatened Species.
Threats
Occurs in an area where the habitat has been destroyed through overgrazing by livestock. The habitat was already severely degraded when the type specimen was collected in the 1920s. There is a possibility that this species is already extinct.

  
Conservation Underway
No conservation measures are underway for this species which may already be extinct.
Conservation Proposed
Further surveys to determine the conservation status of this species.
References
Kerbis Peterhans, J. & Lavrenchenko, L. 2008. Nilopegamys plumbeus. In: IUCN 2011. IUCN Red List of Threatened Species. Version 2011.1. <www.iucnredlist.org>. Downloaded on 13 August 2011.

Peterhans, J.C.K. and Patterson, B.D. 1995. The Ethiopian water mouse Nilopegamys Osgood, with comments on semi-aquatic adaptations in African Muridae. Zoological Journal of the Linnean Society, 113: 329–349.

Nowak, R.M. 1999. Walker's Mammals of the World. The Johns Hopkins University Press, Baltimore, USA and London, UK.

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