Rattus ceramicus Thomas, 1920

Rattus ceramicus Thomas, 1920

Type material studied. The holotype ( NHMUK ZD 1920.7.26.28 ; Figs 5–10 View Figure 5 View Figure 6 View Figure 7 View Figure 8 View Figure 9 View Figure 10 ) is an adult male collected at 6000 feet (1830 m) on Gunung Manusela, Seram Island , South Maluku ( Fig. 1 View Figure 1 ). The label indicates “trapped in heavy jungle.” Collected by the Pratt brothers in January 1920 and described by Oldfield Thomas in the same year ( Thomas, 1920) . Two other specimens were collected by the Pratt brothers at the same altitude (NHMUK ZD 1920.7.26.29 and NHMUK ZD 1920.7.26.30). All of these specimens are held by the Natural History Museum, London (NHMUK).

Referred specimens. Another adult male was trapped in 1987 by a Western Australian Museum field crew headed by D. J. Kitchener (WAM M33490; Helgen, 2003).

Taxonomic history. Thomas (1920) originally described R. ceramicus as a species of Stenomys based on his concept of the genus at that time, although he noted that the new species only superficially resembled Stenomys from New Guinea (“this species … is really very different”) based on features of the auditory bullae and palate. In the past, small mountain rats from New Guinea were most commonly placed in this genus (type species Stenomys verecundus ), which is currently synonymized with Rattus . Thomas (1922) later established a monotypic genus, Nesoromys , for ceramicus , an arrangement maintained by Aplin et al. (2003) and Musser & Carleton (2005), but not supported by our results (although there is a broader potential need to redefine the generic name of Rattus from the Australo-Papuan region, the Maluku Islands, and also the Rattus xanthurus species group from Sulawesi; see ‘Discussion’ below). On the basis of our molecular results and our morphological comparisons, we definitively place the species here within a monophyletic radiation of Australo-Papuan and Moluccan Rattus (see Discussion) and recover it as the sister species of Rattus feliceus , another Seramese endemic ( Fig. 2 View Table 1 View Figure 2 ).

Distribution. Rattus ceramicus has only been recorded from Gunung Manusela, but may also occur in other higher elevation areas on Seram. Its recorded altitude range is 1500–1830 m ( Helgen, 2003).

Emended diagnosis. Rattus ceramicus is a small rat with soft and dull rufous fur covering both the upper and lower parts of the head and body ( Fig. 5 View Figure 5 ). This species is characterized by the following features: (1) a dark brown monochromatic tail almost equal to the length of the head and body (TL/ HB = 104–107%; Table 2 View Table 2 ); (2) long hind feet relative to the length of the head and body; (3) weak interorbital and postorbital ridges and only weakly developed temporal ridges ( Fig. 6 View Figure 6 ); (4) the bony palate protruding well beyond the upper molar 3 to form an extensive bony shelf, which is the most distinctive feature of this Rattus species ( Fig. 7 View Figure 7 ); (5) a narrow zygomatic plate and shallow zygomatic notch ( Fig. 8 View Figure 8 ); (6) a long and narrow rostrum; (7) viewed laterally, the dorsal outline of the skull forms a convex arc between the nasal tips and the occipital bone; (8) the zygomatic arch is broadly widened parallel to the upper dentary; (9) in ventral view, the squamosal root of the zygomatic arch is anterior to the level of the tympanic bulla; (10) in ventral view, the maxillary root of the zygomatic arch is placed at the level of the first upper molar (M1); (11) the posterior margins of the very short incisive foramina terminate well anterior to M1; (12) the condyloid process of the dentary is elongated, upwardly directed and curved; (13) the angular process does not project beyond the posterior part of the condyloid process and is not well developed; (14) the incisors are opisthodont with a narrow tip blade that is smaller than its longest basal width (an abnormal notch is present on the upper incisor in the specimen vouchered as WAM M33490); (15) a posterior cingulum is present on M1 but is weakly developed ( Fig. 9 View Figure 9 ); (16) cusp t3 is present on M2 but absent on the third molar; (17) t1 bis is present on the first maxillary molar; (18) cusp t1 of M1 is either at the same level as or slightly posterior to cusp t3, cusps t1 + t2 + t3 form a U-shaped lamina; (19) anterolabial and posterolabial cusplets are present on lower molar 1 (m1; Fig. 10 View Figure 10 ); (20) an anterolabial cuspid and posterolabial cusplet are present on m2 of the holotype, but a comparable cusplet is not visible on the other NHMUK and WAM specimens; (21) m3 has an anterolabial cuspid but lacks a posterolabial cusplet.

Ecology. Nothing is known about the ecology of this species except that it was collected in primary montane forest at 6000 ft (about 1830 m). It co-occurs with species of Melomys ( Melomys aerosus , Melomys fraterculus , Melomys fulgens , and Melomys paveli ) as well as Rattus feliceus and the two introduced species of Rattus found in Seram mountains— R. nitidus and R. exulans ( Helgen, 2003) . Judging by its relatively short tail and elongated hind feet, R. ceramicus is probably terrestrial in lifestyle.