Chiromyscus thomasi, Balakirev, Alexander E., Abramov, Alexei V. & Rozhnov, Viatcheslav V., 2014

Balakirev, Alexander E., Abramov, Alexei V. & Rozhnov, Viatcheslav V., 2014, Phylogenetic relationships in the Niviventer-Chiromyscus complex (Rodentia, Muridae) inferred from molecular data, with description of a new species, ZooKeys 451, pp. 109-136 : 121-124

Taxon classification Animalia Rodentia Muridae

Chiromyscus thomasi sp. n.

Holotype.

ZMMU S-191982, body in ethanol, skull extracted, genetic code MC68, adult male, collected 17 December 2011 by Alexander E. Balakirev. GenBank IDs: JQ755933, JQ755964, KF154025, KF154068.

Type locality.

Vietnam, Son La Province, Muong Thai Village, near Lung Lo pass, 21°18'31"N, 104°41'34"E, elevation ~ 450 m above sea level.

Paratype.

ZIN 101651, body in ethanol, skull extracted, genetic code MC80, adult female, collected 17 December 2011 by Alexander E. Balakirev from the type locality. GenBank IDs: JQ755934, JQ755965, KF154069).

Referred material.

BMNH 25.1.1.110, skin and skull, male, Bao Ha, Lao Cai Province, Vietnam; BMNH 26.10.4.167, skin and skull, female, Dak To, Kon Tum Province, Vietnam; BMNH 26.10.4.166, skin, male, Xieng Kuang, Laos.

Diagnosis.

This species is set apart from all other described species within the genus Chiromyscus by the following combination of morphological traits: (1) Appreciably larger size. This species is the largest in size of any species of Chiromyscus . Head and body length is 145-180 mm, tail length 200-231 mm, length of hind foot 27-29 mm, ear length 18-20 mm, greatest skull length 41.0-43.0 mm, upper molar lengths 7.0-8.0 mm; the supraorbital ridges are more developed than in other species, forming a distinct pointed triangle shelf at the point where the frontal and palatal bones come into contact. This shelf is very perceptible in the frontal view of the skull. (2) The upper parts are orange-brown. From the face to behind the ears, the pelage is bright orange, with a prominent darker ring around the eye forming a “mask” on the face. The under parts are pure white and sharply demarcated from the upper parts. The feet and toes are generally white with orange hairs on top. The tail is bicolored, dark on top and appreciably lighter below, where there is a pinkish hue. The hallux is shortened with rounded nails instead of pointed claws. The species is well differentiated genetically from other Chiromyscus . The DNA sequences that are deposited in GenBank under IDs JQ755933-JQ755934, JQ755964-JQ755965, KF154025 and KF154068-KF154069 may be used as genetic vouchers for this species.

Description.

The fur is dense, smooth and downy. The coloration of the upper side is a bright fulvous with a perceptible orange hue, which is most prominent in the humeral area. On the underside, the belly is pure white without patches or creamy hues. The sides are more brightly colored than the back. The cheek, lateral surface of the neck and the front legs are a bright yellowish-orange. The rump, hips, and base of tail are also, like the cheek, a rich ochraceous color. A very prominent black strip passes over the eye, forming a very characteristic “mask” on the face. The vibrissae are long (over 60 mm), both black- and white-colored, and the ears are small (18-20 mm), pale-brown colored and rounded. The dorsal sides of both the front and hind feet are completely buffy-orange. The pads both in the front and hind feet are well developed. The claws are large (4.2-5.0 mm in length), curved and appreciably sharp. The hallux bears a plain nail instead of a claw. The tail is very long, slender and hairy; it is much longer than the body (128-132% of body length). It is rather thick and almost uniformly tinged pale-brown from the proximal part to the tip.

Comparisons.

Chiromyscus thomasi is a brightly colored species, a feature that obviously distinguishes it from Chiromyscus langbianis , which is generally dull in coloration. With its bright fulvous or orange coloration Chiromyscus thomasi is similar to Chiromyscus chiropus but may be distinguished from it by its dorso-ventral coloration demarcation line. In Chiromyscus thomasi , the white-colored belly replaces the bright orange ventral side coloration abruptly, without any intermediate zone, whereas a lighter-colored fulvous intermediate zone (0.5-1.0 cm in width) is perceptible on the back sides of Chiromyscus chiropus . However, the most apparent distinguishing feature of Chiromyscus thomasi is a dark “mask” on the face around the eyes, which may be used to visually separate it from any another Chiromyscus or Niviventer species. Chiromyscus thomasi is the largest species in the genus, appreciably bigger than Chiromyscus chiropus and Chiromyscus langbianis . Its skull well exceeds the known range of size variation for other Chiromyscus as well as for the majority of Niviventer species, with the exception of Niviventer tenaster and the " andersoni " group, both of which are roughly equal in size to, or larger than, Chiromyscus thomasi . In comparison with other Chiromyscus species, the skull of Chiromyscus thomasi is also the most “heavily-built”, with supraorbital ridges that are more developed, forming prominent wide shelves. The skull of Chiromyscus langbianis is much smaller and gracile, and the shelves are not so apparent, whereas in Chiromyscus chiropus the skull has an obviously convex profile (when viewed from the side), in contrast with Chiromyscus thomasi , which appears rather flattened when viewed from the side.

Etymology.

The new species is named in honor of Oldfield Thomas (1858-1929), the British zoologist who named and described the genus Chiromyscus and the species chiropus .

Common name.

Thomas' masked tree rat.

Distribution.

Confirmed specimens of Chiromyscus thomasi have been recorded from the provinces of Son La and Lao Cai in northern Vietnam, the provinces of Kon Tum and Nhge An in central Vietnam, and the provinces of Xieng Khouang and Luang Prabang in northern Laos, based on published data and our (BAE) most recent and unpublished data. This species may have a wider distribution in central Vietnam ( Dang Huy Huynh et al. 1994, Dang Ngoc Can et al. 2008) and in northern and central Laos ( Aplin et al. 2008, Musser 1981, Corbet and Hill 1992) where similar “mask-bearing” specimens have been reported. It is also likely distributed in south-western China (see Wang 2003) and northern Thailand (see Marshall 1977) but clarifying comparisons are needed to rule out alternative identifications ( Chiromyscus chiropus and Chiromyscus langbianis ) before this wider potential geographic distribution is confirmed.