Leptomys signatus Tate and Archbold, 1938

Musser, Guy G., Helgen, Kristofer M. & Lunde, Darrin P., 2008, Systematic Review of New Guinea Leptomys (Muridae, Murinae) with Descriptions of Two New Species, American Museum Novitates 3624 (1), pp. 1-60 : 31-34

Leptomys signatus Tate and Archbold, 1938

HOLOTYPE AND TYPE LOCALITY: The holotype of signatus is AMNH 105792 , an adult female, represented by an intact skull and study skin, from the ‘‘east bank’’ (5 north bank) of the Fly River opposite Sturt Island (‘‘ Sturt Island Camp’ ’, Rand and Brass, 1940: 361; [ Papua New Guinea, Western Province]), near sea level, 08 ° 159S, 142 ° 159E, and collect- ed October 12, 1936 by G.H.H. Tate. Skin of the holotype is shown in figure 4, a skull from the original series is illustrated in figure 9, and measurements of the holotype are listed in table 1.

GEOGRAPHIC DISTRIBUTION: We identify samples of Leptomys signatus that were collected from three sites in south-central New Guinea, located in Western, Southern Highlands, and Gulf provinces of Papua New Guinea. The specimens come from an altitudinal range extending from near sea level to 1400 m .

The four specimens in the type series of L. signatus were taken in the Trans-Fly region along the southern Fly River in Western Province (locality 2 in gazetteer and fig. 2), and until now these have been the only published records of the species. Two additional specimens, previously undocumented, originate from the north-northwestern slopes of Mount Bosavi (locality 3, gazetteer and fig. 2), where they were trapped at 1400 m by A.B. Mirza ( BBM-NG 103319 and 103263); no other information is available about these Bosavi examples, which, judging from the trapping altitude, were taken in lower montane rain forest, a different type of habitat than recorded for L. signatus elsewhere.

Leary (2004) collected and discussed the most recent sample of L. signatus to have been collected, which consists of two specimens trapped on the Darai Plateau, 380 m, in Gulf Province (locality 4, gazetteer and fig. 2). We have not studied these vouchers, but Leary provided us with photographs in support of the record (see fig. 15), demonstrating that both specimens exhibit a conspicuous pale spot on the head as well as other associated biological data that we exhibit below. However, some specimens of L. elegans show weak to moderate white markings between the eyes, so the skulls of the Darai specimens will have to be examined to confirm their identification as L. signatus .

These additional specimens ( Mount Bosavi , and probably Darai Plateau) replicate the distinctive morphological attributes of the type series of L. signatus and extend the known distribution of this species more broadly throughout the lowland drainages of south-central New Guinea. We expect that the species extends much farther to the west as well, especially to other forested landscapes throughout the western portion of the Trans- Fly region (extending across the border between Indonesia and Papua New Guinea), an area that has received comparatively little attention in biological surveys ( Helgen and Oliver, 2004) .

DIAGNOSIS AND CONTRASTS: The diagnostic traits that Tate and Archbold (1938) used to separate L. signatus from L. elegans and L. ernstmayri (short, dense fur and grayish brown upperparts with a large and conspicuous white blaze on the head) identify a highly distinctive southern New Guinean population of Leptomys . The pale terminal tail tip is longer relative to tail length, and hind foot longer but wider relative to body size in L. signatus than in all other species of Leptomys (tables 2, 3). In body size, L. signatus is larger than L. ernstmayri and L. paulus , n. sp. (see accounts of those species and compare tables 2 and 3), smaller than L. elegans , and equivalent to L. arfakensis , n. sp. (table 2). That similarity between the latter and L. signatus also extends to length of tail relative to body length, in which the tail is about the same length as head and body in L. signatus and the Arfak species, but shorter in L. elegans and markedly longer in L. ernstmayri and L. paulus , n. sp. (tables 2, 3).

Leptomys signatus and L. elegans closely resemble each other in cranial and dental dimensions (table 4), but L. signatus is set apart from L. elegans by morphometric contrasts (figs. 13, 14). For example, whether the first canonical variate is contrasted with either the second or third extracted from discriminant-function analyses, scores representing specimens of L. signatus form a tight constellation separate from those identifying L. elegans and L. arfakensis , n. sp., along the first canonical axis. This isolation of L. signatus is influenced primarily by its proportionately narrow and short rostrum (rostral length is measured by length of nasals), narrow zygomatic plate, and heavy molars (tables 4, 7).

Of the two qualitative dental traits we surveyed, the second upper molar in L. signatus possesses cusp t7 but lacks an anterolabial cingulum (table 6). Cusp t7 is present in about three-fourths of our sample of both L. elegans and L. ernstmayri , but is absent in samples of L. paulus , n. sp., and L. arfakensis , n. sp. In addition to L. signatus , an anterolabial cingulum is absent in the two new species and most examples of L. elegans , but in only about 40% of the specimens of L. ernstmayri .

HABITAT AND BIOLOGY: Leptomys signatus is certainly terrestrial, likely nocturnal, but most other biological attributes have yet to be revealed. Although it has long been known only by the type series from the Fly River Basin, and thus considered an exclusively lowland species ( Musser and Carleton, 1993, 2005; Flannery, 1995), the series from the northern slopes of Mt. Bosavi demonstrate that the altitudinal range of L. signatus is similar in vertical extent to that of L. elegans (see account of L. elegans ). The mean altitude of the three known trapping sites is 593 m (median 380 m, SD 724 m).

According to Rand and Brass (1940:361), the type locality of L. signatus (the Sturt Island Camp ), was :

situated in a grove of bamboos on the top of a red bluff, about 12 m. high, overlooking the river. …Bordering the river in many places are muddy tidal terraces with tall forests dominated by a mangrove ( Bruguiera ), and a nutmeg with a highly developed system of aerial roots.…The general terrain is of irregular lateritic ridges, among which are enclosed flat basins, for the most part swampy, and connected with the river by sometimes almost imperceptible watercourses which empty into muddy tidal creeks.…With the exception of the wetter flats, where transitions from rainforest to swamp-forests of tea-tree and sago and eventually open reed swamps occur, the whole area is covered with rain-forest.

Rand and Brass (1940: 361–363) provided excellent descriptive views of the different vegetative formations along with photographs of the bamboo substage of dry, open rainforest, and different kinds of tall swamp forests in the dry season. The region around Sturt Island Camp in that part of the Fly

TABLE 7 Results of Discriminant-Function Analysis Performed on 23 Adult Leptomys with Larger Body Size: Leptomys elegans , Leptomys signatus , and Leptomys arfakensis (Correlations, eigenvalues, and cumulative variance are explained for three canonical roots; see table 4, figs. 13, 14. We used 10 variables instead of the 17 utilized in our other multivariate analyses to accommodate both skulls representing L. arfakensis , neither of which is complete.)

River was a mosaic of rain forest; sago, Melaleuca , and other kinds of swamp forests; and open marsh and swamp (see their summary of habitat types and map, Rand and Brass, 1940: 372–373). According to the collectors of the type series, within this complex mosaic of habitats, Leptomys signatus inhabits ‘‘well-drained forests bordering the north banks of the Fly River’’ ( Tate and Archbold, 1938: 1).

Leary (2004) noted that:

Two individuals were caught on the Darai Plateau, a sub-adult male and a pregnant female. These traps were set in a drainage line that flooded during heavy rain, but the water soon dissipated through limestone crevices after the rain ceased. The female was pregnant with a single embryo. They were both caught in small Elliot traps baited with singed coconut and set on the ground.