Rattus morotaiensis Kellogg, 1945

Rattus morotaiensis Kellogg, 1945 View in CoL

The distinctive extant murine Rattus morotaiensis was originally described by Kellogg (1945) from a series of specimens collected on the island of Morotai. More recently, specimens of native Rattus from the North Moluccan islands of Halmahera and Bacan have been referred to this species (Flannery, 1995a; Hasegawa & Syaffrudin, 1995b) and a similar species has more recently been collected from Obi ( Fabre et al., 2023). However, specimens from islands other than Morotai have now been shown by Fabre et al. (2023) to represent two distinct species, Rattus halmaheraensis (recorded from Halmahera, Bacan, Ternate, and Moti) and Rattus obiensis (recorded from Obi). Three partial dentaries and one isolated upper incisor from Daeo Cave no. 2 are referred to R. morotaiensis ( Figs 3–5 View Figure 3 View Figure 4 View Figure 5 ; Table 1 View Table 1 ). Measurements of these and several modern specimens of R. morotaiensis are shown in Table 1 View Table 1 . The subfossil specimens are an excellent match in both size and morphology for modern voucher specimens.

Rattus morotaiensis is a distinctive taxon with broad, lowcrowned molars and crenulated enamel ( Figs 3–5 View Figure 3 View Figure 4 View Figure 5 ). It differs in many ways that can be observed in subfossil remains from those of similar-sized commensal Rattus such as R. rattus and R. nitidus . In the upper dentition of R. morotaiensis , the posterocone is present on M 1 and cusp t1 of the M 1 is placed just below the level of cusps t2 and t3, and M 2 exhibits wide cingular margins and a cusp t3. The first lower molar is particularly distinctive, with a short anterior lamina that consists of subequal anterolabial and anterolingual cusps separated by a deep anterior groove. The middle and posterior laminae are weakly folded. There are large and distinctive peg-like anterolabial and anterolingual cusplets on m 1 and m 2, anterolabial and posterolabial cusplets on m 1 and m 2, and an anterolabial cusplet on m 3. The dentary is unusual in having an elongate and broad condylar process that projects behind the angular process.