Rattus morotaiensis Kellogg, 1945

Rattus morotaiensis Kellogg, 1945 View in CoL

Type material studied. The holotype ( USNM 277312 ) is an adult male collected on Morotai (= Morty) Island on 25 October 1944 by J. F. Cassel and R. M. Roecker and described by Kellogg (1945) . Six other specimens were also collected from the same locality (USNM 277309–277311; 277313–277315).

Type locality. The type locality is Morotai Island, North Maluku, Indonesia.

Referred specimens. One specimen was collected in 1991 by Indonesian mammalogist Boeadi (AM M.26618) on Morotai Island. We also examined modern (AM M.7083– 7086) and subfossil specimens of Rattus morotaiensis discussed by Aplin et al. (2023).

Distribution. Rattus morotaiensis is thus far known only on Morotai Island. All specimens have so far been collected at low elevations.

Emended diagnosis. Rattus morotaiensis is a medium to large rat with a spiny coat that is dark reddish brown ( Table 2 View Table 2 and Fig. 15 View Figure 15 ). This species of Rattus is characterized by the following features: (1) a dark brown tail longer than its head and body length (TL/HB = 109–126%, Fig. 3 View Figure 3 ), sparsely haired and slightly tufted at the tip; (2) long hind feet relative to head and body length for this presumably scansorial or arboreal rat species ( Table 2 View Table 2 ); (3) the postorbital ridge is well developed and marked, and the temporal ridge is well developed ( Fig. 6 View Figure 6 ); (4) the palatal bridge moderately extended behind M3 ( Fig. 7 View Figure 7 ); (5) the zygomatic notch is moderately wide and the rostrum is short and narrow; (6) laterally, the skull is almost flat between the nasal and occipital (or slightly curved between the interparietal and frontal; Fig. 8 View Figure 8 ); (7) in lateral view the zygomatic arch well upon the level of the upper molar row; (8) in ventral view, the zygomatic root of the zygomatic arch does not reach or just overlaps the level of M1; (9) posteriorly, the incisive foramina are short and just reach or do not reach the front of M1; (10) the usual mammae formula is 1 pectoral + 1 post-axillary + 0 abdominal + 3 inguinal (1+1+0+3=10), but one specimen has eight mammae (one of the paratypes from Morotai lacks a pair of pectorals, but see description in Kellogg, 1945); (11) the angular process does not extend behind the posterior part of the condylar process and is not very developed; (12) the incisor blade is narrow and its size is less than its longest basal width; (13) the posterocone is present on M1 ( Figs 9 View Figure 9 and 13 View Figure 13 ); (14) cusp t3 is present on M2 and usually on M3; (15) cusp t1 of M1 is located just behind the level of cusps t2 and t3; (16) there are large and prominent peg-like anterolabial and anterolingual cuspids on m1 ( Figs 10 View Figure 10 and 14 View Figure 14 ); (17) anterolabial and anterolingual cuspids on m1 are of almost equal size; (18) anterolabial and posterolabial cusplets are present on m1 in most specimens, the anterolabial cusplet always being smaller than the anterolabial cuspid on m1; (19) a wide cingular margin is present on m2; (20) an anterolabial cuspid is always present on m2 and m3; (21) a posterolabial cusplet is always present on m2 and absent on m3; (22) strongly crenulated enamel is present on all molars.

A detailed description of Rattus morotaiensis was also provided by Kellogg (1945), and a detailed comparison between R. morotaiensis and the two Rattus species from Halmahera and Obi can be found in the descriptions below.