Niviventer cremoriventer (Miller, 1900)

Ge, Deyan, Feijó, Anderson, Abramov, Alexei V., Wen, Zhixin, Liu, Zhengjia, Cheng, Jilong, Xia, Lin, Lu, Liang & Yang, Qisen, 2021, Molecular phylogeny and morphological diversity of the Niviventer fulvescens species complex with emphasis on species from China, Zoological Journal of the Linnean Society 191 : -

NIVIVENTER CREMORIVENTER ( MILLER, 1900)

( FIG. 5E 1–E 4)

Sundaic arboreal niviventer or dark-tailed tree rat.

Mus cremoriventer Miller, 1900 a: 144 . Southern peninsular Thailand, Trong, Trang Province, Thailand.

Mus flaviventer Miller, 1900 b: 204 . Puki Jimaja, Anambas Islands.

Mus gilbiventer Miller, 1903: 35 . Sullivan Island, Mergui Archipelago, Burma.

Mus kina Bonhote, 1903: 124 . Mount Kinabalu, Borneo.

Epimys barussanus Miller, 1911: 26 . Mojeia River, Nias Island , Sumatra.

Epimys mengurus Miller, 1911: 27 . Bukit Menguru, Billiton Island , Sumatra.

Epimys spatulatus Lyon, 1911: 111 . Pulo Lamukotan, Borneo.

Epimys solus Miller, 1913: 22 . Pulo Teratau Island, Malay Peninsula.

Rattus cremoriventer cretaceiventer Robinson & Kloss, 1919: 377 . Tjibodas, Java.

Rattus cremoriventer malawali Chasen & Kloss, 1932: 32 . Mallewalle Island, Borneo.

Rattus cremoriventer sumatrae Bartels, 1937: 123 . Bandjarnegri, Wai Semangka, Lampoengs, Sumatra.

Holotype: USNM 86770 , skin and skull of an adult male collected by W. L. Abbott on 16 January 1899. Mountain of Trong , Trang Province, Lower Siam ( Thailand), at approximately 900 m, approximate coordinates: 7.433 N, 99.85 E.

Measurements (in mm): EMs and CMs of holotype provided by Miller (1900) are as follows: total length = 317, HBL = 146, TL = 171, pencil at the tip of the tail = 8, EL = 17, ear from crown = 13 and width of ear = 12. Greatest length of skull = 34, basal length = 28, basilar length = 25, palatal length = 13.4, least width of palate between anterior molars = 3.4, diastema = 8.2, length of incisive foramen = 5.6, combined breadth of incisive foramina = 2.6, length of nasals = 11.8, combined breadth of nasals = 4, zygomatic breadth = 15.4, interorbital breadth = 6, mastoid breadth = 12.8, breadth of braincase over roots of zygomata = 14.8, depth of braincase at front of basioccipital = 10, frontal–palatal depth at posterior extremity of nasals = 7, least depth of rostrum immediately behind incisors = 6, maxillary toothrow (alveoli) = 6, width of front upper molar = 1.6, mandible = 15.6 and mandibular toothrow (alveoli) = 6.

BM (g), EMs and CMs (mean ± 1 SD, range, mm) from museum specimens: BM = 62.1 ± 6.40 (51–68, N = 10). EMs of ten adult specimens: HBL = 133 ± 6.04, TL = 178.13 ± 14.80, HFL = 26.80 ± 0.92 and EL = 19.20 ± 1.03. CMs from 29 intact adult specimens: TLC = 34.67 ± 1.41, NL = 12.31 ± 0.59, GWS = 5.78 ± 0.58, SDO = 5.93 ± 0.25, ZB = 15.50 ± 0.93, GMB = 13.87 ± 0.68 , PL = 16.66 ± 0.74, IFL = 5.59 ± 0.49, WIF = 2.52 ± 0.20, GPB = 6.72 ± 0.27, LTB = 5.29 ± 0.39, ULMM = 5.67 ± 0.24, ULMD = 8.83 ± 0.59, ML = 15.99 ± 0.69, LLMM = 5.69 ± 0.20 and LLMD = 4.57 ± 0.46. Original measurements are given in Supporting Information, Table S2.

Diagnosis: Niviventer cremoriventer is a mediumsized species with spines mixed with soft hairs on the dorsum. Dorsal coloration is overall bright orange or reddish brown and more yellowish on the sides. Feet have an overall brown colour and are covered with fine, short, white hairs. Tail is uniformly dark with a short tuft at the tip. Skull of N. cremoriventer is appreciably gracile, with undeveloped supraorbital ridges and the rostrum is narrow.

Distribution: This species occupies the widest distribution range of members of the NFSC and is widely distributed in the Malay Peninsula, Sunda Islands and Southeast Asia. It was also discovered in Modao River, Jingdong, Yunnan Province, China.

Comments: Musser (1973) presented a detailed description of the external and craniodental features of the species and discussed the taxonomic identity of N. cremoriventer in relation to similar taxa from Southeast Asia. Musser (1973, 1981) considered the Indochinese species N. langbianis ( Robinson & Kloss, 1922) as the closest morphological and likely phylogenetic relative of N. cremoriventer , which is now assigned to a species in the genus Chiromyscus ( Balakirev et al., 2014; Jing et al., 2007). However, these two species differ in the colour of the pelage and the size and proportions of external, cranial and dental features. The brownish grey upper parts with pale yellow and olive tones of C. langbianis are in striking contrast to the orange or reddish brown upper parts of N. cremoriventer ( Musser 1973) . Balakirev et al., (2014) published figures of the holotype of N. cremoriventer (see fig. 6 in Balakirev et al., 2014) and noted that the tail of this species was long, slender and hairy. These characteristics are different from those of other species within the NFSC.

The wide distribution of N. cremoriventer in Southeast Asia requires a more detailed study of the genetic diversity and morphological differentiation of this species, which might include cryptic species ( Denys et al., 2017). However, the present study included only data from GenBank, leaving a large area in Southeast Asia unsampled. Therefore, the intraspecific genetic differentiation of this species could not be clarified here.

Sympatric species: In China, N. cremoriventer has an overlapping distribution with C. langbianis , N. bukit , and N. mekongis . It is a typical rat of low and middle elevations (183–275 m) with a uniformly dark tail.