Chiruromys forbesi Thomas 1888

Chiruromys forbesi Thomas 1888, Proc. Zool. Soc. Lond., 1888: 239.

Type Locality: Papua New Guinea, Central Province, Astrolabe Range, Sogeri, 1500 ft (458 m).

Vernacular Names: Forbes's Chiruromys.

Synonyms: Chiruromys major (Tate and Archbold 1935); Chiruromys mambatus (Thomas 1920); Chiruromys pulcher Thomas 1895; Chiruromys satisfactus (Tate and Archbold 1935); Chiruromys shawmayeri (Laurie 1952); Chiruromys vulturnus (Thomas 1920) .

Distribution: Papua New Guinea; endemic to mainland of SE Papua New Guinea, sea level to 700 m. Not recorded west of Oomsis Creek in valley of Markham River (see map of this region in Brass, 1959), and extends eastward to Bara Bara near Milne Bay (Thomas, 1897 a); also on D'Entrecasteaux Isls (Goodenough, Fergusson, and Normanby). Occurs in lowlands (sea level to 700 m) on the mainland, but up to 1300 m on Goodenough Isl and nearly 900 m on Normanby Isl (Flannery, 1995a, and specimens in AMNH). Dennis and Menzies (1979) included the Louisiade Isls in the range, but samples in AMNH of Chiruromys from there are not forbesi but examples of a separate undescribed species (Musser and Lunde, ms).

Conservation: IUCN – Lower Risk (lc).

Discussion: Significance of the appreciable geographic variation in body size and other traits recently assessed by Musser and Lunde (ms) who provided results of multivariate analysis of morphometric variation in samples from the mainland of E Papua and the three largest D’Entrecasteaux Isls (Goodenough, Fergusson and Normanby). Within the island samples, that from Goodenough averages larger in cranial dimensions than the other two, and as a group the three insular samples average larger than those from mainland Papua in both cranial and dental dimensions. The names satisfactus and major were applied to samples from Goodenough Isl (Tate and Archbold, 1935), and shawmayeri to specimens from Fergusson Isl (Laurie, 1952).

The contrast between mainland and insular populations reflects some evolutionary divergence in the island populations after separation from the mainland at the end of the Pleistocene when sea levels rose. The D’Entrecasteaux Isls are on the continental shelf and have likely been either connected to or separated from mainland Papua at several times during glacial and interglacial Pleistocene intervals, which provided intermittent periods of gene flow between island and mainland populations. Islands in the Louisiade Arch., far eastward of the mainland, are surrounded by deeper seas and past connection with the mainland was either tenuous or nonexistent, which is reflected in the significant differentiation of the populations of Chiruromys (an undescribed species; Musser and Lunde, in ms.) and Melomys (undescribed species related to M. lutillus; see that account) that are endemic to Sudest Isl in the Louisiades.