226.

Uneven-toothed Rat

Anisomys imitator

French: Anisomys / German: Hornchenzahnratte / Spanish: Rata de dientes irregulares

Other common names: Husk Shredder, Squirrel-toothed Rat

Taxonomy. Anisomys imitator Thomas, 1904,

“Avera, Aroa River, British New Guinea [= Central Province, Papua New Guinea].”

J. R. Ellerman in 1941, citing cranio-dental features, considered A. imitator to be among the most primitive of living Muridae, an interpretation reinforced in 1969 by X. Misonne’s more detailed analysis of dental characters. Molecular evidence places Anisomys among Australo-Papuan Hydromyini but fails to identify any close relative. Geographic variation has not been critically assessed by morphometric or genetic studies. Currently regarded as monotypic but in need of further assessment.

Distribution. New Guinea, including the Central Cordillera from Weyland Range E to Owen Stanley Range, Cromwell and Rawlinson ranges on Huon Peninsula, and Mt Dayman in Maneau Range on SE peninsula, at elevations of ¢.500-3500 m.

Descriptive notes. Head—body 215-285 mm, tail 275-359 mm, ear 16-26-3 mm, hindfoot 56-66 mm; weight 280-580 g. The Uneven-toothed Rat is a moderately large scansorial murine of typical body proportions but with some peculiar dental specializations. Fur on upperparts is short (c.12 mm) and mildly stiff to touch, strongly brindled owing to black or dark brown tipping on yellowish-brown body hairs and guard hairs, latter projecting ¢.2-3 mm and most prominent along mid-back and on rump; flanks slightly paler or with more orange; underparts white, sometimes with pale gray underhairs, softer texture, extending onto inner surfaces of limbs and throat but not to chin, which is dark; boundary between flank and belly coloration is sharp. Head is robust, relatively deep but not broadened, fur gray around mouth but black on vibrissal pads; eyes of normal size, ringed with black fur; ears short and rounded, dark gray and thinly furred; vibrissae coarse and very long, extending past shoulders. Skin of foreand hindfeetis spotted dark and with black hairs almost to tips, terminal pads unpigmented and with shortsilvery hairs; forefeet with white claws on four digits; hindfeet moderately long and heavy, lacking webbing between digits, and with heavy white claws on all digits, plantar pads moderately large and prominent. Tail is very long, 113-127% of head-body length, basal 20-50% gray, remainder white or pale cream, with sharp boundary between two sections; tail scales hexagonal, flat, and non-overlapping, 8-9 rows per cm at mid-tail;each scale with three hairs that are equal in length to one scale, overall appearance oftail being slightly hairy; tip oftail has short brush but lacks prehensile modification. Three mammae on each side, one post-axillary and two inguinal. Cranium is robust, with proportionally small auditory bullae and molars; upper and lower incisors “uneven”—uppers of normal proportions paired with lowers that are extremely narrow and deep, a condition unique within Murinae; molars with distinctive laminar crown pattern. Subadult individuals have dull gray, less brindled pelage. Karyotype 2n = 46, autosomes predominantly acrocentric but largest pair submetacentric. Prominent centromeric C-bands on all pairs, except one small metacentric pair and very small Y chromosome. Spermatozoa with long tail (144 pm), sperm head broad basally, tapering to a long (5 pm) apical hook, and lacking accessory ventral hooks.

Habitat. All records are from evergreen tropical rainforest, ranging from lowland hill forest at lowest elevations to mossy upper montane forest at highest. Some captures have been made in gardens and patches of secondary forest within a broadly forested landscape.

Food and Feeding. T. F. Flannery reported “soft white pulp” in stomach of one individual. Experienced local hunters in several parts of Papua New Guinea describe the Uneven-toothed Rat’s preference for fruits of Pandanus palms, as well as nuts and fruits of many kinds of trees. Camera trap images show individuals of the rat foraging on ground and carrying fruits by mouth. According to Flannery, Telefol hunters of West Sepik Province tie woven plastic sacking around base of cultivated Pandanus palms to snare individuals of this murid that attempt to feed on the clusters of fruit. S. Majnep, a Kalam hunter from the Schrader Range, Madang Province (Papua New Guinea), reported that this common species (Kalam name Kmn-gudl-ws) feeds on fallen fruits of Pandanus palms (wild and domesticated), nuts and fruits of several trees ( Garcinia, Clusiaceae; Artocarpus, Moraceae; Elaeocarpus, Elaecocarpaceae), and the fruits of Ficus that grow in cauliflorous manner from bases of the tree. He also reported that Pandanus fruit in particular is carried away from initial feeding site (behavior observed on camera-trap images), and sometimes stored in dens; further, that some are dehusked and,after sprouting, deliberately planted to promote new tree growth. While some aspects of Majnep’s account seem allegorical, they nonetheless represent a reminder of the important role in seed dispersal played by many larger rodents in tropical forests. Majnep also claimed thatit is the Black-tailed Giant Rat ( Uromys anak) that typically cuts down the large fruiting bodies of Pandanus, the Uneven-toothed Rat and other, smaller murine rodents merely feeding on the fallen bounty.

Breeding. P. Dwyer’s notes on 22 individuals recorded in 1985 on Mount Sisa, Southern Highlands Province, Papua New Guinea, suggest breeding activity during the “ Pandanus season” (October—March), when this high-rainfall area experiences slightly higher average daily temperatures and longer periods of sunshine between rainfalls. A subadult male with non-descended testes weighed 390 g, while reproductively mature males all weighed in excess of 500 g. Reproductively mature females with enlarged teats weighed 490 g or more, while females with non-enlarged teats weighed 465 g or less. Individuals weighing 400 g or less retained the duller,less brindled immature pelage. According to Majnep, the Uneven-toothed Rat constructs nests of foliage on the ground, either in swordgrass ( Imperata cylindrica, Poaceae) beds or under base ofa tree fern ( Cyatheaceae) or beneath fallen tree branches. In both positioning and construction its nest resembles those of bandicoot ( Peramelidae), and it is most often captured by women hunting for these common marsupials.

Activity patterns. Camera-trapping images at ground level are obtained exclusively at night. Body form of the Uneven-toothed Rat suggests ascansorial lifestyle.

Movements, Home range and Social organization. Camera-trapping results only rarely feature more than one individual. This suggests that the species is effectively solitary and that weaning young do not move around to any significant extent with adults. Majnep’s account does not allude to any communal nesting for this species.

Status and Conservation. Classified as Least Concern on The IUCNRed List. Lower part of elevational range of the Uneven-toothed Rat coincides with a zone of extensive habitat modification owing to long-term subsistence agriculture and, more recently, extensive forestry activity. Habitats above 2500 m are much less affected by subsistence activities but, inplaces within the Uneven-toothed Rat’s range, they are potentially impacted by large-scale resource-development projects. Although this species is often said to be rare, it has proven to be moderately abundant in a number of widely scattered regions, e.g. Snow (= Surdiman) Mountains of Papua Province, in Indonesia, and, in Papua New Guinea, in upper Fly catchment (Western Province), upper Kikori catchment (Gulf Province), and slopes of Mount Dayman, Maneau Range (Milne Bay Province).

Bibliography. Breed & Aplin (1995), Donnellan (1989), Dwyer (1990), Ellerman (1941), Flannery (1995b), Flannery & Seri (1990), Hide et al. (1984), Leary, Seri et al. (2016), Majnep et al. (2006), Menzies & Dennis (1979), Misonne (1969), Musser & Carleton (2005), Rowe et al. (2008), Rimmler (1938), Tate (1951), Thomas (1904), Watts & Baverstock (1994a).