Dibamus montanus Smith, 1921

Kliukin, Nikita S., Nguyen, Tan Van, Pawangkhanant, Parinya, Pham, Hieu Minh, Le, Son Xuan, Gorin, Vladislav A., Bos, Collin, Krone, Isaac W. & Poyarkov, Nikolay A., 2025, A new species of Dibamus from the Central Highlands of Vietnam with redescription of Dibamus montanus Smith, 1921 (Squamata: Dibamidae), Zootaxa 5693 (1), pp. 1-31 : 9-18

Dibamus montanus Smith, 1921

( Figs. 3 , 4D–I , 5 , 6D–F , 7B , 8 ; Tables 4–5 )

Chresonymy:

Dibamus montanus — Smith (1921: 431–432); Dao (1979: 3); Greer (1985: 149); Bobrov (2008: 98); Bourret (2009: 309); Nguyen et al. (2009: 240); Poyarkov et al. (2023: 285).

Type specimens: lectotype NHMUK 1946.8.3.3 ( adult male); paralectotype NHMUK 1946.8.3.2 ( adult female); both designated by Greer (1985).

Type locality: Le Bosquet , Langbian Plateau , Vietnam ( now near Da Tho Ward , Dalat City, Lam Dong Province, Langbian Plateau, southern Vietnam; geographic coordinates N 11.93255°, E 108.53316°; elevation 1,340 m asl.).

Suggested common names: Langbian Blind Skink (English), Thằn lằn giun Lang Biang (Vietnamese), Langbianskaya cherveobraznaya yascheritsa (ЛангбианскаЯ червеобраЗнаЯ ЯЩерица, Russian).

Referred material: Morphological redescription of D. montanus is based on re-examination of two type specimens ( lectotype NHMUK 1946.8.3.3 and paralectotype NHMUK 1946.8.3.2) and examination of the two newly collected adult male specimens ( ZMMU Re-18136 and ZMMU Re-18137), both from Di Linh District, Lam Dong Province, Vietnam. Specimens were collected from a coffee plantation located 3 km northwards from Di Linh ( 11.617°N, 108.075°E; elevation 955 asl.), by N. A. Poyarkov, P. Pawangkhanant, and H.M. Pham on September 08, 2022. We also refer one damaged adult female specimen VRTC NAP-04859 (former ZMMU Re-18138; not included in the morphological description) collected from the same locality by T.V. Nguyen on August 11, 2022 to Dibamus montanus .

Revised diagnosis. Dibamus montanus can be distinguished from all other congeners by the following combination of morphological characters (based on Greer [1985] and this study): (1) maximum SVL of 130 mm; (2) tail comparatively long, TL comprising 17.3–18.4% of SVL; (3) medial rostral, labial, and nasal sutures present and complete; (4) one postocular scale; (5) two to three scales bordering the posteromedial edge of the first infralabial; (6) the medial sublabial scale not enlarged; (7) 20–22 midbody scale rows; (8) 19–23 transverse scale rows just posterior to head; (9) 21–23 transverse scale rows just anterior to vent; (10) 187–225 ventral scales; (11) 45–49 subcaudal scales; (12) relative size of frontal to frontonasal 116.9–138.4%; (13) relative size of interparietal to nuchal scale 148–188.7%; and (14) the light-colored band on the body incomplete.

Morphological description of the lectotype (NHMUK 1946.8.3.3). An adult male, a specimen in a good state of preservation ( Fig. 3A ); for measurements, see Table 4 ; SVL 130.0 mm; tail length 22.7 mm (17.5% of SVL); head longer (HL 6.5 mm) than wide (HW 4.3 mm); snout bluntly rounded, projecting beyond the jaw ( Fig. 3B , Fig. 4G ); E-S 0.6 mm; E-N 1.7 mm; IN 1.1 mm; OI 2.5 mm; labial and nasal sutures present and complete; rostral suture present and complete ( Fig. 3B , Fig. 4G ); rostral pad with a large number of evenly distributed sensory papillae; single postocular scale on each side; ear opening absent; eyes barely visible below the single ocular scale; supralabial single ( Fig. 3B , Fig. 4G ); frontal scale slightly larger than frontonasal scale ( FSW / FNSW 128.4%); interparietal single, not enlarged, narrower than frontonasal and frontal, posteriorly bordered by four slightly smaller nuchals ( Fig. 4H ); infralabials lanceolate, separated by a smaller mental; mental narrow, trapezoid in shape, bordered by the first infralabial on each side; two scales contacting the first infralabial, a small medial scale posterior to the mental, and three larger scales contacting the infralabial posteromedially ( Fig. 4I ). Body wormlike, almost cylindrical; body scales smooth, subcycloid ( Fig. 3 ); 22 midbody scale rows; 19 scale rows just posterior to head; 21 scale rows anterior to vent; 49 subcaudals; 206 ventrals; tail complete, rudimentary flap-like hind limbs present (HLL 2.8 mm) ( Fig. 3C ); medial scales near vent elongated, lanceolate ( Fig. 7B ); tail tip blunt, covered by a single rounded scale, not terminating in a spine. Morphometric data of the specimen are presented in Table 4 .

Coloration. Coloration in life is described on the basis of newly collected specimens from Di Linh ( Fig. 5A ) and one not collected specimen from Di Linh ( Fig. 5B ). In life, dorsum, flanks, and tail reddish-brown to pale brown ( Fig. 5 ); head, snout, and ventral surfaces slightly paler; rostral and mental pads, anal region, and tip of legs lighter, cream-colored. Distinct dull-grey transverse body band at the front part of the body or at the midbody, incomplete, with irregular shape ( Fig. 5 ); large irregular grey spots on the dorsum and a large light-grey spot anterior to the vent. In preservative after approximately one year of storage in ethanol, the general coloration pattern does not change, though reddish and brownish slightly fade to dull brown or beige.

Variation. The measurements of the newly collected series ( ZMMU Re-18136 and ZMMU Re-18137) and the lectotype and paralectotype (NHMUK 1946.8.3.3 and NHMUK 1946.8.3.2) revealed high variability in several morphological characters ( Table 4 ). Head scalation of ZMMU Re-18136 is shown in Figure 6D–F ; its cloacal region is detailed in Figure 7B . The male lectotype NHMUK 1946.8.3.3 and the female paralectotype NHMUK 1946.8.3.2 have a greater snout-vent length than ZMMU Re-18136 and ZMMU Re-18137 ( SVL 130.0 mm and 120.0 mm vs. 87.6 mm and 81.0 mm, respectively), which may be related to the different age of the specimens in these series. The specimens NHMUK 1946.8.3.3 and NHMUK 1946.8.3.2 exhibit a slightly higher number of midbody scale rows ( MBSR 22), while the specimens ZMMU Re-18136 and ZMMU Re-18137 have 21 and 20 midbody scale rows, respectively ( MBSR, see Table 4 ). In addition, the number of scale rows just posterior to the head varies from 19 (in NHMUK 1946.8.3.3) to 23 (in NHMUK 1946.8.3.2) (PHSR, Table 4 ), while the number of scale rows just anterior to the vent varies from 21 (in ZMMU Re-18136 and ZMMU Re-18137) to 23 (in NHMUK 1946.8.3.3 and NHMUK 1946.8.3.2) ( VSR, Table 4 ).

Variation was also observed in the number of subcaudal scales. In female paralectotype NHMUK 1946.8.3.2, the number of subcaudal scales is 43 (SC, Table 4 ), while in other specimens it was notably higher ( 46 in ZMMU Re-18136, 47 in ZMMU Re-18137, and 49 in NHMUK 1946.8.3.3). Finally, the male specimen ZMMU Re-18137 has only two scales on the posteromedial edge of the infralabial, while all other specimens have three scales on the posteromedial edge of the infralabial (PIS, Table 4 ). Furthermore, we observed an abnormal structure of the frontonasal scale in the specimen ZMMU Re-18137, in which this scale is divided by an additional suture that is absent in other specimens.

Hemipenial morphology. The morphology of the hemipenial structures is unknown, as in all specimens these structures were not everted prior to preservation.

Osteological description. The following description of skeletal features of Dibamus montanus is based on the microCT data obtained from the male specimen ZMMU Re-18136. Skeletal morphology of this specimen is presented in Figure 8 ; osteological terminology generally follows Greer (1985), Rieppel (1984), and Kliukin et al. (2023, 2024a, 2024b). Skull elongated, small relative to the body; shoulder girdle absent; pelvic girdle and rudiments of hind limbs present ( Fig. 8A ). Body with 116 presacral vertebrae, 2 distinct sacral vertebrae, and 26 tail vertebrae ( Fig. 8A ). The pelvic girdle includes the fused ilium, ischium, and pubis; hind limbs include the femur, tibia, fibula, and a rudimentary bony cap ( Fig. 8E–F ).

The premaxilla is an unpaired bone ( Fig. 8B–D ); the transverse process of the premaxilla is pierced by paired apical foramina. Four labial foramina are present on both the left and the right maxilla. Each of the maxillary bones bears eight slightly curved teeth ( Fig. 8D ). The nasal bones are distinct, perforated by four foramina on each side ( Fig. 8C ). The prefrontal is a triangular bone forming the posterodorsal edge of the lacrimal foramen. The lacrimal, postfrontal, postorbital, jugal, and epipterygoid bones are absent. The paired frontals form the anteromedial processes dividing the posterior portions of the nasals ( Fig. 8C ), the anterolateral processes (lateral prongs) of the frontals are relatively long. The unpaired parietal bone forms supratemporal processes that overlay the dorsal portions of the prootics and a wide posterior medial process that meets the supraoccipital in a suture ( Fig. 8C ). The medial (sagittal) ridge on the parietal is relatively small ( Fig. 8C ). The vomers, palatine, pterygoids, and ectopterygoids are paired bones ( Fig. 8B ) with morphology similar to that described for the other members of the genus Dibamus by Greer (1985) and Kliukin et al. (2023, 2024a, 2024b).

The parabasisphenoid complex (corresponding to the ‘parasphenoid + basisphenoid’ of Rieppel 1984) forms a broad, massive bone meeting the basioccipital with a distinct suture. Exoccipitals, basioccipitals, supraoccipitals, prootics, and opisthotics are separate bones ( Fig. 8 B-D). The stapes is characterized by a broad stapedial footplate slightly elongated anteroposteriorly ( Fig. 8D ). The quadrate bone is short and flattened; its vertical axis is slightly tilted posteriorly.

Five labial foramina are present on the right side of the dentary ( Fig. 8D ), and four labial foramina are present on the left side of the dentary. The dentary bears eight teeth on each side. Coronoid process of the dentary is comparatively small; a distinct coronoid bone is present. The compound bone is formed by the fused splenial, articular, angular, and supraangular bones; the retroarticular process of the compound bone is comparatively short ( Fig. 8D ). The lower jaw with mandibular, anterior, and posterior supraangular foramina.

Distribution and natural history notes. The status of the earlier records of Dibamus montanus from other parts of Southeast Asia ( Laos, Cambodia, and southern Vietnam) is addressed in detail in the Discussion section; below we demonstrate that all these records are based on misidentifications with other species of Dibamus . Dibamus montanus is therefore endemic to the Langbian Plateau in southern Vietnam and is currently reliably known from three localities, all located in Lam Dong Province: from the environs of Dalat City (locality 12, see Fig. 1 ) and from the environs of Di Linh Ward (localities 13–14, see Fig. 1 ). The locality 14 from Suoi Lanh Stream, Gung Re Commune, ca. 12 km South of Di Linh District, Lam Dong Province, is based on a photographed and not collected specimen ( Fig. 5B ), which generally agrees with the description of D. montanus presented above for the characters that can be examined from the photo.

The type locality of D. montanus at Le Bosquet in Da Lat City (now Da Tho ward, 11.93255°N, 108.53316°E; elevation 1,340 asl.) currently represents a heavily modified habitat in the eastern suburbs of the Da Lat City with pine groves formed by Pinus kesiya Royle ex Gordon and Pinus dalatensis Ferré. In Di Linh District, the two adult male specimens of D. montanus ( ZMMU Re-18136 and ZMMU Re-18137) were collected in a heavily modified habitat on a coffee plantation at the base of a single tree in an area of 1 m 2 ( Fig. 9 ) by N.A. Poyarkov, P. Pawangkhanant, and Pham Minh Hieu on September 8, 2022 (geographic coordinates N 11.61551°, E 108.07204°; elevation 946 m asl.). This habitat is located 3 km North of Di Linh Ward, and all the area around represents farmland without any remnants of forest.

One additional specimen ( ZMMU Re-18138) of D. montanus was collected from the same location near Di Linh Ward by T.V. Nguyen on August 11, 2022. The specimens were hiding in leaf litter, under fallen logs, and in the upper layer of soil. The sympatric species of reptiles recorded in the same habitat in Di Linh City include Indotyphlops braminus (Daudin) and Scincella sp. In Suoi Lanh Stream, Gung Re Commune, South of Di Linh District, D. montanus was recorded in secondary montane polydominant forest within ca. 10 m of the bank of the Suoi Lanh stream ( 11.47117°N, 108.07013°E; elevation 1,190 m asl.). The male specimen ( Fig. 5B ) was collected from under a flat stone near the forest trail; when uncovered, it tried to retreat by digging in the soil. The secondary montane evergreen forest in Gung Re Commune, Di Linh District, is strongly impacted by various anthropogenic pressures including logging, industrial crop planting, and the establishment of new coffee plantations. Sympatric lizard species recorded in the Gung Re Commune, Di Linh District, include Lipinia microcercus (Boettger) , Scincella sp. ( Scincidae ), Cyrtodactylus cf. irregularis (Smith) , Gekko trinotaterra (Brown) ( Gekkonidae ), Acanthosaura murphyi Nguyen, Do, Hoang, Nguyen, McCormack, Nguyen, Orlov, Nguyen & Nguyen , Acanthosaura coronata Günther , Paracalotes microlepis (Boulenger) , and Bronchocela vietnamensis Hallermann & Orlov ( Agamidae ). Reproductive biology, diet, enemies, and parasites of D. montanus remain completely unstudied.

Conservation status. Though our study expands the known distribution of Dibamus montanus to the Di Linh ward and Gung Re communes of the Di Linh District of Lam Dong Province, southern Vietnam, this species still appears to be a narrowly distributed endemic of the Langbian Plateau. During recent years, forest communities of southern Vietnam, including the Lam Dong Province, have been subjected to progressively growing pressure from intensifying logging and farming activities ( De Koninck 1999; Laurance 2007; Meyfroidt & Lambin 2008, 2009; Meyfroidt et al. 2013; Quy et al. 2018). The greatest threat for the montane forests of the Langbian Plateau is habitat loss and degradation due to logging and the progressing industrial crop cultivation, construction, and tourism development in Lam Dong Province. We demonstrate that in the Di Linh area, D. montanus is recorded in both forested areas and in the completely transformed agricultural landscapes lacking any remnants of forest. We also note that sometimes this species is killed by local farmers due to confusion with snakes. Therefore, we propose to classify this species as a Vulnerable (VU) species following IUCN’s Red List categories ( IUCN Standards and Petitions Subcommittee 2019).

Figures

FIGURE 1. Distribution of the genus Dibamus in southern Indochina. Dot in a center of a symbol marks the type locality of a species; colors of symbols correspond to those used in Figure 2. Localities: Laos: 1—Pakxong District, Champasak Province (FMNH 258662); Vietnam: 2—Sao La Nature Reserve, A Luoi District, Thua Thien-Hue Province (Nguyen et al. 2009); 3—Son Tra Nature Reserve, Da Nang City (Phan et al. 2021); 4—Ngoc Linh Nature Reserve, Kon Tum Province (Le et al. 1999); 5— Kon Chu Rang Nature Reserve and Tram Lap, Gia Lai Province (Darevsky 1992); 6—Buon Luoi, Gia Lai Province (Darevsky 1992); 7—Kon Ka Kinh National Park, Gia Lai Province (this work); 8—Da Ban Lake, Ninh Hoa District, Khanh Hoa Province (Greer 1985; Darevsky 1992); 9—Hon Ba Nature Reserve, Khanh Hoa Province (Bobrov 2008); 10—low elevations of Nui Chua National Park, Ninh Thuan Province (Kliukin et al. 2023); 11—Nui Chua Mountain, Nui Chua National Park, Ninh Thuan Province (Kliukin et al. 2024a); 12—Le Bosquet, Da Lat City, Lam Dong Province (Smith 1921); 13—Di Linh Town, Di Linh, Lam Dong Province (this work); 14—Suoi Lanh, Gung Re, ca. 12 km southwards from Di Linh, Lam Dong Province (this work); 15—Binh Chau-Phuoc Buu Nature Reserve, Ba Ria-Vung Tau Province (Ineich 1999); 16—Con Dao National Park, Ba Ria-Vung Tau Province (Honda et al. 2001); Cambodia: 17—Phnum Bokor Mountain, Preah Monivong Bokor National Park, Kampot (Kliukin et al. 2024b); 18—Dalai Mountain, Phnom Samkos Wildlife Sanctuary, Pursat Province (Neang et al. 2011); Thailand: 19—Khao Soi Dao Wildlife Sanctuary, Chanthaburi Province (Honda et al. 1997).

FIGURE 3. Male lectotype of Dibamus montanus (NHMUK 1946.8.3.3) in preservative.A—right lateral view of the specimen, scale bar equals 10 mm; B—photograph of head scalation (in lateral view); С—cloacal region and hindlimbs (in ventral view). Photographs by Collin Bos.

FIGURE 4. Line drawings of head scalation of the holotype of Dibamus annae sp. nov. ZMMU Re-15720 (A–C), male specimen of D. montanus ZMMU Re-18136 (D–F), and male paralectotype of D. montanus BMNH 1946.8.3.2 (G–I). Head is shown in lateral (A, D, G), dorsal (B, E, H), and ventral (C, F, I) aspects. Scale bar equals 1 mm. Drawings A–F by Nikita S. Kliukin; figures G–I taken from Greer (1985; with permission).

FIGURE 5. Dibamus montanus Smith, 1921 in life. (A) Male specimen ZMMU Re-18136 from Di Linh Town, Di Linh, Lam Dong Province; (B) Male specimen (not collected) from Suoi Lanh, Gung Re, ca. 12 km southwards from Di Linh, Lam Dong Province. Photographs by Parinya Pawangkhanant (A) and Hieu Minh Pham (B).

FIGURE 6. Photographs of head scalation of the holotype of Dibamus annae sp. nov. ZMMU Re-15720 (A–C); and male specimen of D. montanus ZMMU Re-18136 (D–F). Head is shown in lateral (A, D, G), dorsal (B, E, H), and ventral (C, F, I) aspects. Scale bar equals 1 mm. Photographs by Nikita S. Kliukin.

FIGURE 7. Line drawings of cloacal region and hindlimbs of the holotype of Dibamus annae sp. nov. ZMMU Re-15720 (A); and male specimen of D. montanus ZMMU Re-18136 (B). Drawings by Nikita S. Kliukin.

FIGURE 8. Skeletal morphology of the male specimen of Dibamus montanus (ZMMU Re-18136). General view of the skeleton (A); skull in ventral (B), dorsal (C), and lateral (D) views; skeletal structures present in the cloacal region in lateral (E) and ventral (F) views, vertebral column shaded. Terminology follows Greer (1985) and Rieppel (1984). Notes: *—compound bone consists of fused splenial, articular, angular, and supraangular bones (Greer 1985); labial foramina (1)—labial foramina of the maxilla, labial foramina (2)—labial foramina of the dentary.

FIGURE 9. Natural habitat of Dibamus montanus Smith, 1921 at a coffee plantation in Di Linh Town, Di Linh, Lam Dong Province, Vietnam. Photograph by Nikolay A. Poyarkov.