Biswamoyopterus gaoligongensis, Li, Quan, Li, Xue-You, Jackson, Stephen M., Li, Fei, Jiang, Ming, Zhao, Wei, Song, Wen-Yu & Jiang, Xue-Long, 2019

Li, Quan, Li, Xue-You, Jackson, Stephen M., Li, Fei, Jiang, Ming, Zhao, Wei, Song, Wen-Yu & Jiang, Xue-Long, 2019, Discovery and description of a mysterious Asian flying squirrel (Rodentia, Sciuridae, Biswamoyopterus) from Mount Gaoligong, southwest China, ZooKeys 864, pp. 147-160 : 150-157

Biswamoyopterus gaoligongensis sp. nov.

Common name.

Mount Gaoligong Flying Squirrel. Chinese common name "高黎贡比氏鼯鼠".

Holotype.

Specimen KIZ: 034924 (field number bs1628), an adult male, skull, dried skin, baculum, and remaining body part in alcohol deposited in the Kunming Natural History Museum of Zoology, Kunming Institute of Zoology, Chinese Academy of Science (KIZ).

Type locality.

Baihualin village [25.298167N, 98.784683E], Lujiang township, Longyang County, Baoshan City, Yunnan, China. The locality is located on the eastern slope of the southern Mount Gaoligong.

Etymology.

The specific name is derived from Mount Gaoligong, the type locality of the new species and - ensis, Latin for belonging to.

Diagnosis.

Biswamoyopterus gaoligongensis sp. nov. can be distinguished from the other two described species of Biswamoyopterus by the following combination of traits: 1) The ear tufts at the base of the posterior margins of ears are bicolored, basally white and terminal black. The scrotum is dark brown which strongly contrasts with the yellowish-white abdominal pelage. 2) The muzzle is very short, and the zygomatic arch is distinctly expanding outward, making the outline of the skull short and wide. The outer margin of the nasal bone, the orbital margin of the frontal bone, and the post-orbital margin of the frontal bone are almost parallel to the midline of skull on the dorsal view. The central point of the posterior margin of the palatal bones lies in front of the posterior margin of M3. 3) M1 and M2 are sub-square in outline, and as large as P4. The hypoconid of P4-M2 are very developed, strongly pointed towards posterior buccal side.

Description.

Biswamoyopterus gaoligongensis sp. nov. is a large flying squirrel (head and body length: 440 mm, tail length: 520 mm, and body mass: 1370 g) with a very developed uropatagium that extends approximately one-third of the proximal tail length in fresh specimen ( Fig. 4 ). The back and upper surface of patagium are predominantly reddish brown, while the back between the shoulder and uropatagium is speckled with numerous white-tip furs that are absent from the head, shoulder, plagiopatagium, outer edge of uropatagium, limbs, and tail ( Fig. 4 ). Similar to the shoulder, the head is reddish brown, but showing some yellowish grey in the crown. The ear is naked, with two bunches of long hairs (i.e., ear tufts) at the ear base, the anterior tufts are black, and the posterior tufts are basally white and terminal black. The back of each manus is reddish brown and the digits are black, while the whole pes and digits are black. The tail is cylindrical, the part beyond the uropatagium is black, and the part within the uropatagium is the same colour as the uropatagium. Throat, belly, and ventral surface of patagium are yellowish white. However, the scrotum is dark brown which strongly contrasts with the abdominal pelage.

Skull is large with a short muzzle and an expanded outward zygomatic arch, making the outline of skull short and wide ( Fig. 5 ). The frontal depression is deep and postorbital processes are large and well developed. The outer margin of the nasal bone, the orbital margin of the frontal bone, and the post-orbital margin of the frontal bone are almost parallel to the midline of skull on the dorsal view. The auditory bullae are relatively large, with a honeycomb pattern of complex septae. The interpremaxillary foramen is well opened, which is not common in most flying squirrel genera. The mandible is generally similar to that of other flying squirrels. The coronoid process is less developed, only slightly higher than condylar process when the mandible is placed on a plane.

The anterior surface of incisors is pale yellow. Cheek teeth are strongly cuspidate brachyodont, with slightly pitted enamel.

Maxillary teeth: P3 is strong and unicuspid. Parastyle is prominent on P4 and dwindle on the following molars in an anterior to posterior gradient. Paracone is prominent on P4, M1, M2, and M3. Metacone is prominent on P4, M1, and M2, and indistinct on M3. Between protocone and metacone, at the exit of the middle valley of P4, M1, M2, and M3, there are two mesostyles form a projecting gutter. Protocone is prominent on P4, M1, M2, and M3. Hypocone is small, separated from protocone by a notch, distinct on M1 and M2, small on P4, and absent on M3. The anteroloph and posteroloph are indistinct on P4 and M3; distinct on M1 and M2, but they do not develop into a ridge as high as the protoloph and metaloph. A protoloph connecting the protocone with the paracone on M1, M2, and M3, and notched on P4. A metaloph connecting the protocone with the metacone on M2, interrupted by one big or two small metaconules on P4 and M1, and absent on M3.

Mandibular teeth: Four main cusps (protoconid, hypoconid, metaconid, and entoconid) are all distinct on P4, M1, M2, and M3. Mesoconid is present on the buccal side of P4, M1, M2, and M3, the notch between mesoconid and hypoconid is distinct, seems to be formed by the intense wear and tear. Mesostylid is small and fused with metaconid on P4 and M1, indistinct on M2 and M3.

Comparison.

Body size, B. gaoligongensis sp. nov. is similar to B. biswasi but clearly smaller than B. laoensis (Table 1). Pelage colour becomes dark gradually from B. biswasi to B. gaoligongensis sp. nov. and to B. laoensis . The back, B. biswasi is morocco-red speckled with white, B. gaoligongensis sp. nov. is reddish brown speckled with white, and B. laoensis is dark reddish brown speckled with white. The belly, B. biswasi is white, B. gaoligongensis sp. nov. is yellowish-white, and B. laoensis is pale orange. The tail beyond uropatagium, B. biswasi is pale smoky grey, with a dark tip, both B. gaoligongensis sp. nov. and B. laoensis are black ( Fig. 4 ). The ear tufts, B. biswasi are white, B. gaoligongensis sp. nov. are bicolour (the anterior tufts are black, and the posterior tufts are basally white and terminal black), and B. laoensis are black ( Fig. 6 ).

The muzzle of B. gaoligongensis sp. nov. is very short, B. biswasi is intermediate, and B. laoensis is much longer ( Fig. 5 , Table 1). As a result, the outline of skull of B. gaoligongensis sp. nov. is short and wide, B. biswasi is relatively short, and B. laoensis appears long. On the dorsal view of skull, the outer margin of the nasal bone, the orbital margin of the frontal bone, and the post orbital margin of the frontal bone of B. gaoligongensis sp. nov. are almost parallel to the midline of skull, while B. biswasi slanted, and B. laoensis slanted even more. The postorbital processes of B. gaoligongensis sp. nov. and B. biswasi are clearly larger than B. laoensis . The preglenoid process of B. gaoligongensis sp. nov. and B. laoensis are almost flat, whereas that of B. biswasi obviously protruding forward ( Fig. 7 ). The sutures of frontal and squamosal bone of B. gaoligongensis sp. nov. are bulging, while B. biswasi and B. laoensis are almost flat. The auditory bullae of B. gaoligongensis sp. nov. and B. biswasi are distinctly smaller than those of B. laoensis . The posterior margin of the palatal bones of B. gaoligongensis sp. nov. and B. biswasi is concave forward, while B. laoensis is flat. The central point of the posterior margin of the palatal bones of B. gaoligongensis sp. nov. lies in front of the posterior margin of M3, B. biswasi just meet, and B. laoensis lies behind ( Fig. 7 ).

The metacone and hypocone of M1 and M2 of B. gaoligongensis sp. nov. are most developed among three species, followed by B. laoensis , again B. biswasi . As a result, M1 and M2 of B. gaoligongensis sp. nov. are almost equal to P4, while those of B. laoensis and B. biswasi are smaller than P4. In addition, the outline of M1 and M2 of B. gaoligongensis sp. nov. is sub-square, B. laoensis is sub-rectangle, and B. biswasi is sub-triangular. The hypoconid of B. gaoligongensis sp. nov. is strongest among three species, followed by B. biswasi , again B. laoensis ( Fig. 5 ).

Distribution.

Apart from the locality of the holotype, there are two more localities in Yunnan, China, where the Biswamoyopterus gaoligongensis sp. nov. was photographed. These include Linjiapu (25.28693N, 98.70102E), 10 km west of the type locality; and Banchang (25.145876N, 98.796026E), 9 km south of the type locality ( Fig. 1 ). Although these three localities cover the east and west slopes of Mount Gaoligong (the watershed of the Irrawaddy River and the Nu River [Salween River]), they are all restricted in a small area of southern Mount Gaoligong.

Natural history.

Little is known about the natural history of Biswamoyopterus gaoligongensis sp. nov. The holotype was collected from evergreen broad-leaved forest at an altitude of 2,000 meters above sea level. A set of photos taken in Linjiapu showed a Biswamoyopterus gaoligongensis sp. nov. resting on the branches of Daphniphyllum sp. Petaurista yunanensis , P. elegans , and Hylopetes alboniger were also collected in the same habitat where the holotype was collected.

Conservation status.

The limited available information suggests that Biswamoyopterus gaoligongensis sp. nov. has a relatively low abundance. Because low-altitude forests inhabited by Biswamoyopterus gaoligongensis sp. nov. are close to human settlements, they are vulnerable to human activities. The currently known threats are agricultural reclamation and poaching.

Figures

Figure 1. Known localities of three species of Biswamoyopterus.

Figure 4. Skins of the three known Biswamoyopterus species A, B (ZSI 20705, holotype) Biswamoyopterus biswasi C, D (KIZ 034924, holotype) Biswamoyopterus gaoligongensis sp. nov. E, F (NUoL FES. MM. 12.163, holotype) Biswamoyopterus laoensis. The images E, F were derived from Sanamxay et al. (2013).

Figure 5. Skulls, left maxillary (above) and left mandibular (below) tooth rows of the three known Biswamoyopterus species. A (ZSI 20705, holotype) Biswamoyopterus biswasi B (KIZ 034924, holotype) Biswamoyopterus gaoligongensis sp. nov. C (NUoL FES. MM. 12.163, holotype) Biswamoyopterus laoensis. The images of C were derived from Sanamxay et al. (2013).

Figure 6. Ear tufts of the three Biswamoyopterus species, the red arrow indicates the anterior tufts, and the yellow arrow indicates the posterior tufts A (ZSI 20705, holotype) Biswamoyopterus biswasi B (KIZ 034924, holotype) Biswamoyopterus gaoligongensis sp. nov. C (NUoL FES. MM. 12.163, holotype) Biswamoyopterus laoensis. The image C was derived from Sanamxay et al. (2013).

Figure 7. The posterior margin of the palatal bones relative to the posterior margin of M 3 (dotted line) and shape of the preglenoid process (arrow) of the three Biswamoyopterus species A (ZSI 20705, holotype) Biswamoyopterus biswasi B (KIZ 034924, holotype) Biswamoyopterus gaoligongensis sp. nov., C (NUoL FES. MM. 12.163, holotype) Biswamoyopterus laoensis. The image C was derived from Sanamxay et al. (2013).