Crossomys Thomas 1907

Crossomys Thomas 1907, Ann. Mag. Nat. Hist., ser. 7, 20: 70.

Type Species: Crossomys moncktoni Thomas 1907

Species and subspecies: 1 species:

Species Crossomys moncktoni Thomas 1907

Discussion: Hydromys Division. Member of New Guinea Old Endemics (Musser, 1981 c). Based on phallic morphology, Lidicker (1968) speculated that C. moncktoni is not closely related to Hydromys, an affinity supported by microcompliment fixation of albumin that instead clusters Crossomys with Leptomys, Xeromys, and Pseudohydromys (which includes Mayermys and Neohydromys), an assemblage that albumin immunology indicated is part of a larger clade containing members of our Hydromys, Pseudomys, and Uromys Divisions, an "Austalasian clade" (Watts and Baverstock, 1994 a, 1995 b, 1996). Despite the alliance suggested by albumin immunology, we place Crossomys in the Hydromys Division along with Hydromys, Microhydromys, and Parahydromys . Overall morphology of Crossomys, including a shared primitive cephalic arterial pattern, resembles Hydromys and its allies more closely than it does any genus in the Xeromys Division. Unpublished phylogenetic analyses of mtDNA cytochrome b sequences placed Crossomys closer to Hydromys than to Leptomys (K. Aplin, in litt., 2004). Results of the data from microcomplement fixation of albumin (Watts and Baverstock, 1994 a) may not be a reliable indicator of affinities in this case. Crossomys is clearly distant from Hydromys and Parahydromys, but the albumin immunological distances within each group were nearly as great as those between the the group with Hydromys and Parahydromys and the cluster containing Xeromys, Crossomys, Leptomys, and Pseudohydromys (K. Aplin, in litt., 2004). Hydromys, as represented by H. chrysogaster, is an amphibious generalist, utilizing a range of aquatic and semiaquatic prey, from arthropods and mollusks to small vertebrates (Olsen, 1995). Crossomys moncktoni is highly specialized, both in external and cranial morphology for feeding apparently exclusively on aquatic insects, mostly nymphs and larvae (Voss, 1988). Among amphibious muroids, each prey regime exemplified by Hydromys leucogaster and Crossomys is associated with particular external and cranial morphologies (Voss, 1988). In many respects, the cranial specializations of Crossomys form an enlarged version of the cranial conformation characterizing Hydromys habbema (see Flannery, 1995 a:plate 24), which also preys predominantly but not exclusively on aquatic insect larvae and nymphs (Voss, 1988).