223.

Margaret's Ranee Mouse

Haeromys margarettae

French: Haeromys de Margaret / German: Borneo-Zwergbaummaus / Spanish: Raton rani de Margaret

Other

common names: Margaret's Haeromys, Ranee Mouse

Taxonomy. Mus margarettae Thomas, 1893,

“Penrisen Hills, Sarawak,” Malaysia .

This is the type species of Haeromys . In describing Mus margarettae, O. Thomas noted the mosaic of similarities to “ Mus chiropus ” [= Chiromyscus chiropus, a substantially larger arboreal animal] and to other, diminutive, arboreal murines of genera Chiropodomys and Vandeleuria . Subsequently, Thomas concluded that, while margarettae and some closely related species were externally similar to species of Chiropodomys, they were too different in molarcusp arrangement and warranted erection of a distinct genus. G. H. H. Tate in 1936 suggested a possible derivation of Haeromys from his cremoriventer group within “ Rattus ” (now Nwviventer cremoriventer). J. R. Ellerman at first agreed, but by 1949he favored a relationship with Lorentzimys of New Guinea. X. Misonne wrote in 1969 that Haeromys is “extremely difficult to classify” on cranio-dental criteria, while G. G. Musser and C. Newcomb cited cranio-dental evidence in 1983 to align Haeromys more closely to Chiropodomys than to any other genus. Karyotype of Haeromys ( H. minahassae), described by Musser in 1990, conforms closely with putative ancestral arrangementfirst identified among Australo-Papuan members of tribe Hydromyini and also identifiable among Philippine members ofthis phylogenetic lineage. Unpublished cranio-dental studies by K. P. Aplin also point to likely relationship of Haeromys to the Hydromyini, and it is classified as such here, on basis of these converging lines of evidence. Molecular confirmation is required. Taxon pusillus was described as a subspecies by Thomas in 1893, but listed as a full species in 1911 when he specified the content of Haeromys . It was treated as a subspecies by Ellerman in 1941, but returned to species level by Lord Medway in 1965, an action endorsed by Musser and all subsequent authors. A specimen from East Kalimantan reported as H. margarettae by Medway in 1977 was discounted by Musser and Carleton in 1993. Monotypic.

Distribution. Known only from two localities in N & SE Borneo.

Descriptive notes. Head-body 76 mm, tail 144 mm, ear 13 mm, hindfoot 19-7 mm (measurements from type description). No specific data are available for body weight. Margaret's Ranee Mouseis the second smallest native rodent on Borneo; only the Sundaic Ranee Mouse ( H. pusillus) is smaller. It has abroad head with short snout and moderately large eyes. Body proportions are unexceptional, but tail is very long and slender, rather whip-like in appearance. Fur on upperparts is soft, dense, and moderately long, lacking distinct spines. Color described in 1893 by Thomas as “deep rufous chestnut, mixed on the back with the gray of the bases of the hairs, but clearing on the sides where it seems to form a rufous lateral band. Chin, chest, and belly white.” Vibrissae “numerous and prominent, black.” Ears “small, oval, practically naked.” Feet brown but with white skin and hairs on digits. Forefeet with nail on first digit, and “short and curved claws” on remaining digits. Hindfeet are moderately elongate but broad, with six “large rounded pads.” First digit moderately long, and with minute claw rather than a nail; remaining digits all with “very short and curved” claws. Tail is long and slender (190% of head-body length in holotype), and color a “sort of pale greenish gray, the same above as below.”

Basal portion of tail thinly furred but remainderfinely haired, almost naked in appearance, and with small scales, averaging c.17 rows per cm. Cranium has globular braincase, with veryshort, narrow rostrum and delicate zygomatic arches. Three molars present in each series, all very reduced but with cuspidate crown morphology. Mammae three on each side, one post-axillary and two inguinal.

Habitat. The two records are from areas that would have originally supported evergreen tropical rainforest. The lower to middle slopes of Penrisen Hills support dipterocarp hill forest, while upper slopes support lower montane rainforest.

Food and Feeding. Margaret's Ranee Mouse islikely to be a “seed predator.” Breeding. No information.

Activity patterns. Body form suggests a highly arboreallifestyle. Some terrestrial activity is indicated by J. Payne and coworkers’ report of a Haeromys (either this species or the Sundaic Ranee Mouse) captured in a pitfall trap in Sabah, Malaysia.

Movements, Home range and Social organization. No information.

Status and Conservation. Classified as Data Deficient on The IUCN Red List. Type locality is now included within Gunung Niut Penrisen Nature Reserve. In the four decades leading up to 2014, more than 30% of the original tropical rainforest cover of Borneo was lost to habitat conversion, much ofit to oil palm plantations. The range of Margaret’s Ranee Mouse is no doubt both strongly reduced and highly fragmented.

Bibliography. Chasen & Kloss (1932), Corbet & Hill (1992), Donnellan (1989), Ellerman (1941, 1949), Gaveau et al. (2014), Gerrie & Kennerley (2016i), Medway (1965, 1977), Misonne (1969), Musser (1979, 1990), Musser & Carleton (1993, 2005), Musser & Newcomb (1983), Rickart & Heaney (2002), Rickart & Musser (1993), Tate (1936), Thomas (1893d, 1893e, 19111).