Rattus elaphinus Sody, 1941

Rattus elaphinus Sody, 1941 View in CoL

Type material studied. The holotype, an adult female, was collected by J. J. Menden between September and October 1938 on the plains of Taliabu Island ( MZB 4087 ), probably at sea level. The tag indicates the following location: Soela Islands (Sula Archipelago), Taliaboe (Taliabu Island) , “plains”. Sody (1941) did not comment on his choice of “ elaphinus” (“deer-like”) as the species name, but presumably applied it to describe the fulvous dorsal pelage colour exhibited by this species .

Referred specimens. At least 33 specimens of this species were collected by Menden from Taliabu Island. Tim Flannery subsequently collected four specimens on Mangole Island but did not find the species on nearby Sanana Island ( Flannery, 1995).

Diagnosis. Rattus elaphinus is a medium-sized rat with a soft coat that is buffy grey on the underparts and reddish brown on the upper parts ( Fig. 11 View Figure 11 ). This species is characterized by the following features: (1) a monochromatic dark brown tail subequal to the head-body length (TL/HB = 93–102%; Table 2 View Table 2 ); (2) hind feet of medium length in relation to the head-body length; (3) interorbital and postorbital ridges well developed, as well as the temporal ridges ( Fig. 6 View Figure 6 ); (4) the zygomatic plate is broad, the rostrum is moderately long and wide and appears chunky; (5) the palatal bridge projects beyond M3 as a moderately extended bony shelf ( Fig. 7 View Figure 7 ); (6) viewed laterally, the skull is almost flat (slightly convex) between the nasal tip and the occiput ( Fig. 8 View Figure 8 ); (7) the posterior palatal foramina are located between M2 and M3 or at the anterior level of M3; (8) the eustachian tube is short; (9) the post-glenoid cavity is not fused with the middle lacrimal foramen in most specimens; (10) the posterior margins of the wide and long incisive foramina reach M1; (11) the incisor enamel is orange and the upper incisors are either opisthodont or orthodont relative to the rostrum; (12) the incisor blade is wide and equal to or greater than its longest basal width; (13) the posterior cingulum is either absent on M1 or rarely forms a slight bulge; (14) cusp t3 is reduced or absent on M2 but absent on M3 in all specimens observed; (15) t1 bis is absent on M1; (16) cusp t1 of M1 is well separated from cusps t2 and t3; (17) the anterocentral cusplet is absent on m1 ( Fig. 9 View Figure 9 ); (18) anterolabial and posterolabial cusplets are present on m1 in most specimens ( Fig. 10 View Figure 10 ), apart from one individual (MZB 4078) which lacks an anterolabial cusplet; (19) anterolabial cuspid and posterolabial cusplet are present on m2; (20) m3 has an anterolabial cuspid which may disappear with wear in older specimens; (21) the formula for the mammae is 1 pectoral + 1 post-axillary + 0 abdominal + 2 inguinal mammae (1+1+0+2=8).

Comment. No molecular data are yet available for this species. Rattus elaphinus is morphologically very close to the R. leucopus group (an Australo-Papuan lineage; Musser & Carleton, 2005) and in some ways to R. hoffmanni ( Musser & Holden, 1991) and is the only Moluccan Rattus to be included in a previous morphological systematic revision of Rattus , by Musser & Holden (1991), which focused on the systematics of R hoffmanni . As R. hoffmanni is closely related to R. argentiventer ( Rowe et al., 2019) as well as to other Asian Rattus species belonging to the R. rattus and R. norvegicus clades, R. elaphinus may also be closely related to this clade. Sody’s (1941) description of the species is amplified by a detailed description and comparison with R. hoffmanni by Musser & Holden (1991:386–388).

Ecology. Little is known about the ecology of R. elaphinus . All individuals have been caught near sea level ( Flannery, 1995). This species is probably terrestrial in lifestyle, judging from the relative lengths of the tail and hind feet. The Taliabu species R. taliabuensis sp. nov. and R. feileri sp. nov. co-occur with R. elaphinus .