Sicista meiguites Deng Y, Liu Q, Wang XM, Liu SY & Chen SD, 2025

Deng, Yu, Liu, Qing, Wang, Xuming, Li, Binbin V., Wang, Jing, Liu, Shuang, Liao, Rui, Liu, Shaoying & Chen, Shunde, 2025, Molecular phylogeny and taxonomy of the Sicista concolor group (Mammalia, Rodentia, Sicistidae) with the description of a new species, Zoosystematics and Evolution 101 (3), pp. 1197-1211 : 1197-1211

Sicista meiguites Deng Y, Liu Q, Wang XM, Liu SY & Chen SD sp. nov.

Holotype.

SAF 191012 , an adult female collected from Dafengding Nature Reserve in June 2019 by Binbin V. Li. The specimen, preserved as dry skin, skull, and muscle and liver tissues in 95 % ethanol, was deposited at the Sichuan Academy of Forestry. The external and cranial measurements (in millimeters) are as follows: HBL = 64 mm, TL = 117 mm, HFL = 19 mm, EL = 13 mm, PL = 20.96 mm, SBL = 16.33 mm, MPL = 9.95 mm, LBO = 4.14 mm, BB = 9.30 mm, HB = 7.46 mm, ABL = 5.63 mm, UTRL = 9.22 mm, LUM = 3.00 mm, UMRB = 4.10 mm, ML = 12.66 mm, LTRL = 8.29 mm, and LLMR = 3.05 mm.

Type locality.

Dafengding National Nature Reserve , Meigu County, Liangshan Yi Autonomous Prefecture, Sichuan Province, China (28.6116°N, 102.9418°E, 2939 m).

Paratype.

SAF 06183 , SAF 06149 , adult male captured (28.72102°N, 103.27753°E, 2500 m) in June 2006 by SY Liu, Y Liu, YD Li, and J Zhao. SAF 07057 , SAF 07058 , adult male captured on May 12, 2007, by Y Liu and QX Xiao. SAF 191015 , SAF 191178 , SAF 191056 , SAF 191014 , SAF 191056 collected from Dafengding National Nature Reserve in 2019 by Binbin V. Li. All specimens are deposited at the Sichuan Academy of Forestry.

Diagnosis.

This species is distinguished by its unique tail (Fig. 7 b 1 – b 3 ). The tail is darker than that of other species, displaying a deep brown color with a tuft of black hairs at the tip, and its length is approximately twice the length of the body. The palatine foramina are aligned along a line connecting the protocone and paracone of the second upper molar, and the distance between them exceeds the transverse width of the incisive foramen (Fig. 6 b 5 ).

Description.

The head and body length ranges from 53 to 70 mm, tail length from 86 to 145 mm, hind foot length from 16 to 21 mm, ear length from 10 to 17 mm, head length from 18 to 22 mm, and body weight from 6 to 14 g. The upper lip is divided into two segments. The cheeks are tea yellow, extending from the back of the neck to beneath the ears and to the front of the shoulders. Each side has more than 20 vibrissae, with the longest whiskers reaching approximately 30 mm. The longer whiskers are black in the middle and lower parts, grayish-white in the middle and upper parts, while the shorter whiskers are almost entirely grayish-white. The ears are small and round, covered with dark brown short fur. The dorsal fur is dark brown, without any black stripes. The ventral fur has a light gray base with pale yellow tips, and there is no clear demarcation between the back and belly fur. The tail is dark brown and uniformly colored, about twice the length of the head and body. The feet are dark brown, with white toes, and there are long white hair tufts at the base of the claws. The hind limbs are relatively short, with the hind foot length smaller than the total skull length, making them unsuitable for jumping. The forelimbs have four toes, and the hind limbs have five toes (Fig. 7 b 1 – b 3 ).

The cranial region is roughly oval in shape, characterized by a relatively short rostrum. The anterior end of the nasal bone slightly extends beyond the maxillary premaxilla and upper incisors. There is no prominent supraorbital ridge between the orbits. The interorbital region is relatively broad, with the narrowest point located at the midline of the frontal bone. The width of the interparietal bone is about twice its length. The posterior margin of the palatine bone is slightly protruding, extending beyond the posterior margin of the molars. The palatine foramen of the upper jaw are located along the line connecting the protocone and paracone of the second upper molar. The distance between the paired palatine foramina exceeds the width between the lateral margins of the incisive foramen. The coronoid process, condyloid process, and angular process of the mandible are all pointed and slant posteriorly, with thin bones connecting the central region (Fig. 6 b 1 – b 5 ).

The length of the upper dental row ranges from 9.17 to 9.28 mm, and the length of the lower dental row ranges from 8.08 to 8.32 mm. The upper incisors are slender, oriented vertically toward the ventral side, with an orange enamel surface on the labial side, lacking vertical grooves. The lower incisors are white. The width of the upper molar row is 4.10–4.34 mm, and the length is 3.00– 3.12 mm. The upper premolar is very small and cylindrical in shape. The first and second upper molars are well-developed, each bearing four cusps with deep folds on both the inner and outer sides. The anterior margin of the first molar forms a small protuberance that is lower than the cusps. The second molar is equal in size to the first molar. The third upper molar is very small, circular, and shows signs of gradual degeneration. The lower molar row measures 2.90–3.12 mm in length. The mandible contains three molars. The first lower molar aligns with the second upper molar. Both the first and second lower molars are quadrangular, with four distinct cusps and well-developed central depressions. The anterior margin of the first lower molar features a protuberance. The third lower molar is larger than the third upper molar and exhibits a notch along its inner edge (Fig. 6 b 5 – b 6 ).

The glans penis is relatively slender and covered with distinct, evenly distributed keratinized spines. There are 1–2 longitudinal grooves running along the ventral midline and a single longitudinal groove on the dorsal side. The urethral opening is Y-shaped. The outer annular layer lacks papillae, and no urethral valves, dorsal projections, or lateral branches are observed. The baculum exhibits an ossified, rod-like structure without differentiation into distal and proximal ends. The base is slightly concave, and the overall shape is markedly curved towards the ventral side. The ventral tip is Y-shaped, with a central longitudinal groove, and an additional groove is present on the dorsal side (Fig. 5 b 1 – b 4 ).

Comparisons.

Compared to S. concolor , it has a deep, uniformly colored tail measuring over 180 % of the head-body length. The base of the limbs is covered with dark brown fur (Fig. 7 ). In particular, the palatine foramen of the upper jaw is located along the line connecting the original and anterior cusps of the second upper molar, and the distance between the palatine foramen and the incisor foramen margin exceeds the width of the incisor foramen itself (Fig. 6 ). Additionally, the tooth row of S. concolor forms a pronounced arc, with the last pair of molars markedly inclined inward (Fig. 6 a 5 ), whereas S. weigoldi has a straight tooth row (Fig. 6 c 5 ). The new species exhibits an intermediate dental configuration between these two conditions (Fig. 6 b 5 ).

Etymology.

This newly discovered species was found in Meigu, Sichuan Province. In recognition of its type locality, we have named the species accordingly. We propose the English name “ Meigu Birch Mouse ” and the Chinese name “ 美姑蹶鼠 ” for this species.

Distribution.

It is currently known only from Meigu, Sichuan Province, and inhabits the shaded tall grass in montane and subalpine coniferous forests, mixed conifer-broadleaf forests, riverside shrublands, meadows, and alpine grasslands at altitudes ranging from 2000 to 3000 meters.

Figures

Figure 5. Comparison of the glans penis of three species within the S. concolor group. a. Sicista concolor; b. Sicista sp 2; c. Sicista weigoldi. 1. Penis; 2. Midventral cut view of glans; 3. Lateral view of baculum; 4. Dorsal view of baculum. (1) Urethral opening; (2) Outer crater; (3) Glans; (4) Prepuce; (5) Body of penis; (6) Baculum.

Figure 6. Skulls and tooth comparison among species of the S. concolor group. a. Sicista concolor (a 1 – a 6) (museum number: SAF 13331); b. Sicista meiguites sp. nov. (b 1 – b 6) (museum number: SAF 191012); c. Sicista weigoldi (c 1 – c 6) (museum number: SAF 240595).

Figure 7. Pelage and tail comparisons among species of the S. concolor group. a. Sicista concolor (a 1 – a 3) (museum number: SAF 13331); b. Sicista meiguites sp. nov. (b 1 – b 3) (museum number: SAF 191014); c. Sicista weigoldi (c 1 – c 3) (museum number: SAF 240595).