Southern blind tree mouse (Typhlomys taxuansis) from Ta Xua Nature Reserve, Son La, Vietnam

NEWS - Researchers report a little-known rodent species Typhlomys Milne-Edwards 1877 from Son La, Vietnam, with the first morphological and genetic characterization and description of a new species, southern blind tree mouse (Typhlomys taxuansis sp. nov).

Platacanthomyidae is represented by only two genera with 6-7 species and has been considered a mysterious family due to its morphology resembling dormice (Gliridae), the anatomical structure of bullae and dentary more similar to muroids (Miller & Gidley 1918, Musser & Carleton 2005) and the molar occlusal pattern characteristic of Crecitidae (Fejfar & Kalthoff 1999) and Nesomyinae (Ellerman 1940, Ellerman 1949).

The English common name “pigmy dormice” and the Russian common name “Chinese dormouse hamsters” are misleading in this case. Recent taxonomic summaries of mammals have the common name “tree mice”, but consider the most specific features to be “blind tree mice” to distinguish them from other arboreal rodents.

Typhlomys cinereus Milne-Edwards 1877 was described from Fujian, China. Based on differences in body size and coat coloration, several additional taxonomic entities have been described along with a number of related taxa from isolated highland populations in southern and central China and the Hoang Lien Mountains of northern Vietnam.

The subspecies T. c. cinereus, T. c. daloushanensis Wang et Li 1996, T. c. guangxiensis Wang et Chen 1996 and T. c. jingdongensis Wu et Wang 1984 are distributed in China. The Vietnamese population was originally described as a separate species, T. chapensis Osgood 1932, which was long considered a subspecies of T. cinereus until its taxonomic status was restored.

However, the composition of the genus is still not fully clear due to the limited number of specimens, fragmentation and disjunctive patterns of the genus' natural range. The southern limit of the genus' distribution in Indochina and the species composition in Vietnam are still debated. Only a few scientists have been fortunate enough to observe it in its natural habitat in high mountain cloud forests.

The new species was given the Latin name taxuansis referring to the type site in Ta Xua Nature Reserve, the southernmost location currently known for this genus and the researchers proposed "southern blind tree mouse" as the common name in English.

The specimen was captured in a humid and foggy mountain forest at an elevation of 2000-2200 m. Sympatric species include Neotetracus sinensis, Eothenomys miletus, Dremomys ornatus, Dremomys gularis, Niviventer lotipes, Niviventer fulvescens, Mus pahari and Leopoldamys edwardsi which are mostly species of the Chinese mountain fauna complex.

Holotype (mm): BM = 21.10 g; HB = 85.0; TL = 117.0; HL = 25.0; EL = 18.0; ONL = 25.92; ZB = 13.85; IB = 5.59; LR = 8.34; BR = 3.67; BBC = 11.49; HBC = 8.55; ZBP = 1.78; LD = 7.08; LIF = 1.53; BIF = 1.87; LBP = 11.27; BBP = 4.00; PPL = 9.21; BMF = 1.78; LB = 3.42; CLM1-3 = 4.14; BM1 = 1.18; CLM1-3 = 4.29; and BM1 = 1.04.

Vibrissae very long white; ears prominent, almost bare; vestigial eyes. Dorsal body colouration: dark grey; entire ventral body from chin to anus, including inner side of limbs to wrists and knees; greyish due to dark gray hair base and white tip.

Fingers four at fore-limbs and five on hind ones; hind feet slender and elongated (HL = 25 mm); plantar palms of all limbs light brown; fingers pale white; skin on dorsal surfaces of hind feet brownish, covered with slender hair.

Tail long, well exceeding head and body length (TL = 117 mm), with scale rings; proximal third of the tail covered with extremely short and sparse hairs, back part is covered with longer hairs than the ventral side; and the distal half of the tail has tufts of long, dark gray hairs with no white inclusions.

The braincase is generally dome-shaped and relatively high due to its large size (HBC = 8.55 mm). The rostrum is straight beyond the upper incisors. Tympanic bullas are small. Zygomatic plate narrow; zygomatic arch strait, not incurvate on approximately equal thickness throughout its length.

The incisive openings are small, rounded and have a pointed anterior edge. The bony palate is pierced by two pairs of additional symmetrical foramina, with the first pair, located under the rostrum, being approximately half as long as the posterior pair, located between the teeth. Diagonal bone trabeculae are clearly visible deep inside them.

Dental formula is usual for the genus 1.0.0.3/1.0.0.3 = 16. M1, with almost equally wide anteroloph and posteroloph. M1 antherophosette is divided into two separate parts. The first molars of the upper jaws have six dark fossette-shaped structures; the first lower molars have only five dark fossette-shaped structures; the second upper and lower ones have four fosettes; and the third molars have two and four.

The mesofossette on M1 is open on only the lingual sides. M2 with anterofossette, divided by a complete, well developed mesofosette; m1 with two antherofossettids and a closed mesofossettid. Anterofossettids are present in m2, but relatively short. m3 mesolophid has a crescent shape due to the facet protruding from the lingual side.

The new species is currently only obtained from the site type, but may also be distributed in adjacent mountainous areas in northwestern Vietnam, north of the Da River. There is a close genetic similarity between the specimen and the Yunnan finds.

T. taxuansis is similar to T. daloushanensis, but differs based on dental and skull morphology. The closest genetic lineage is T. fengjiensis. Genetic relationships with species of the cinereus group, which are widely distributed in central and eastern China, suggest that the species' range may extend eastward to northeastern Vietnam and Guanxi Province in China.

Based on the ecological characteristics of the habitat, the species may also spread eastward south, for example in the Annamite Mountains, both on the Laotian and Vietnamese sides, but there is still no record of finds south of the Da River.

Original research

Balakirev A, Phuong B, Rozhnov V (2024). Typhlomys taxuansis (Rodentia, Platacanthomyidae): new species of the genus from northern Vietnam with notes on conservation status and distribution. Biodiversity Data Journal 12: e133363, DOI:10.3897/BDJ.12.e133363

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