Dixonius sambhupura, Pauwels & Das & Jocqué & Sumontha & Donbundit & Magda & Sonet & Brecko & Meesook, 2025

Dixonius sambhupura sp. nov.

( Figures 1–6 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 ).

Dixonius siamensis View in CoL — Bezuijen et al. 2009: 145 (partim)

Dixonius sp. — Jocqué et al. 2018: 47

Dixonius siamensis View in CoL — Pauwels et al. 2020: 108 (Cambodian specimens)

Dixonius siamensis View in CoL — Sumontha & Pauwels 2020: 176 (Cambodian specimens)

Dixonius siamensis View in CoL — Pauwels et al. 2021: 538 (Cambodian specimens)

Holotype. RBINS 2743 About RBINS (formerly under RBINS 18573); adult male collected on 3 May 2018 in a cultivated field (12°34’02.9”N, 105°56’55.9”E) near Chrouy Banteay , in Prek Prasab Wildlife Sanctuary, 5 km W of the Mekong River, about 10 km NW of Kratie, Kratie Province, Cambodia. Holotype and all paratypes collected by the BINCO field team GoogleMaps .

Paratypes (9). All from Kratie Province, Cambodia: RBINS 2744 About RBINS (formerly RBINS 18571), adult female collected on 9 May 2018 near Kaoh Khlab (13°00’37.6”N, 106°03’52.7”E), on Koh Klap, an island on the Mekong River , Ou Krieng, in Sambor Wildlife Sanctuary GoogleMaps ; RBINS 2745 About RBINS (formerly RBINS 18572), adult female collected on 7 May 2018 near Kaoh Khlab (13°00’03.4”N, 106°03’14.1”E) on the same island on the Mekong River , Ou Krieng GoogleMaps ; RBINS 2746 About RBINS (formerly RBINS 18574), subadult female collected on 8 May 2018 near Kaoh Khlab (13°00’36.0”N, 106°03’54.0”E) on the same island on the Mekong River , Ou Krieng GoogleMaps ; RBINS 2747–2749 About RBINS (formerly RBINS 22394– 22396), respectively adult female, adult female and adult male (hemipenes partly everted) collected on 4 May 2022 in a cultivated field (12°34’01.1”N, 105°56’55.9”E) near Chrouy Banteay , 5 km W of the Mekong River GoogleMaps ; RBINS 2750–2752 About RBINS (formerly RBINS 22397–22399), respectively adult female and two juveniles collected on 4 May 2022 among bushes bordering a cultivated field (12°34’01.1”N, 105°56’55.6”E) near Chrouy Banteay , 5 km W of the Mekong River GoogleMaps .

Diagnosis. Dixonius sambhupura sp. nov. can be distinguished from all other congeneric species by the combination of its maximal known SVL of 49.0 mm; 14 or 16 longitudinal rows of dorsal tubercles; 34–37 paravertebral tubercles; 24–27 longitudinal rows of ventrals across the abdomen; six precloacal pores in males, no pores in females; 12–14 subdigital lamellae on the 4th toe; no marked canthal stripe; strongly barred lips; and a spotted dorsal pattern in adult males and females.

Description of holotype. Adult male ( Figures 1 View FIGURE 1 and 2 View FIGURE 2 ). SVL 46.5 mm. Head relatively long (HL/SVL ratio 0.31), wide (HW/HL ratio 0.67), not markedly depressed (HD/HL ratio 0.45), distinct from neck. Lores and interorbital region weakly inflated. Canthus rostralis relatively prominent. Snout moderately short (SnOrb/HL ratio 0.40), rounded, about twice as long as orbit diameter (OrbD/SnOrb ratio 0.49). Scales on snout and forehead small, hexagonal to rounded, slightly domed. Scales on snout slightly larger than those on occipital region. Eye of moderate size (OrbD/HL ratio 0.20). Pupil vertical with crenelated margins. Ciliaries short, the anterior ones forming small conical spines. Ear opening oval, small (EarL/HL ratio 0.07); orbit to ear distance greater than orbit diameter. Rostral 1.35 times wider than high, dorsally divided by a median cleft prolonged by a small hexagonal scale enclosed within the rostral, the lowest point of this small scale reaching the mid-height of the rostral. Two enlarged supranasals, separated by a smaller scale. Rostral in contact with supralabial I on each side, nostrils and three supranasals. Nostrils rounded, each surrounded by supranasal, rostral, supralabial I and two postnasals. Mental triangular, wider than long. Two pairs of enlarged postmentals, anteriormost approximately four times larger than posterior. Each anterior postmental bordered anteriorly by mental, medially by the other anterior postmental, anterolaterally by infralabial I and a small scale posterior to infralabial I (left) or by infralabials I and II (right), posterolaterally by the second postmental; the pair collectively bordered posteromedially by a row of five throat scales. Supralabials to mid-orbital position 6/6; enlarged supralabials to angle of jaws 7/7. Infralabials 7/7. Interorbital scales 10.

Body slender, elongate (TrunkL/SVL ratio 0.42), without ventrolateral folds. Dorsal scales small, irregular, flattened to conical, distributed among large, strongly keeled tubercles arranged in 14 more or less regular longitudinal rows at midbody. Paravertebral tubercle rows separated by two or three granular scales, i.e. about the width of a tubercle. Lower flanks covered with irregular, smooth to slightly domed scales. Gular region with relatively homogeneous, granular scales. Ventral scales smooth, imbricate, their free margin rounded. Ventrals increasing in size from throat to chest to abdomen. Midbody scale rows across belly to lowest rows of tubercles 25. Six precloacal pores in a continuous series. No femoral pores or enlarged femoral scales.

Fore- and hind limbs relatively short, slender (FaL/SVL ratio 0.14; TibL/SVL ratio 0.17). Digits slender, dilated distally, bearing robust, slightly recurved claws. Fourth finger of right hand mostly missing (healed). Only four toes on right pes (two toes seem fused). Basal subdigital lamellae narrow, without scansorial surfaces (7-9-10-10- 9 left manus; 7-10-12-13-13 right pes); setae-bearing lamellae restricted to enlarged, distal, ‘‘leaf-like’’ scansors. Scales on palm and sole small, smooth to domed, rounded to oval. Interdigital webbing absent. Relative length of digits: III>II≈IV>V>I (manus), III≈IV>V>II>I (pes). Tail length 13.0 mm, of which the last 2.6 mm correspond to the regenerated part of the tail. Supracaudals keeled on the original part of the tail. Six subcaudals enlarged into transverse plates on the original part of the tail.

Coloration in life. Dorsal surface of head gray brown with irregular black patches. Supralabials with each a wide, vertical black bar. No strongly marked canthal stripe. Neck gray brown with on each side an elongate, irregular black patch. Dorsum gray brown with a series of five irregular vertebral black spots between limb insertions, and elongate black patches on the upper flanks. Flanks gray brown with irregular black spots. Dorsal surfaces of members gray brown with scattered black and white small spots. Upper surface of the original part of the tail gray brown with black spots and white dots. Throat, lower flanks and belly dark gray, darker on the underside of limbs and tail, with irregular, whitish dots.

Cranial osteology. Based on the adult female paratype RBINS 2750 ( Figure 6 View FIGURE 6 ).

Snout complex: Single dentigerous premaxilla bearing 11 teeth and elongated, tapering ascending process.

Paired, elongated, laminar nasals with an anterior, tapering process clasping the premaxillary ascending process. Paired, ventrally concave septomaxillae, with a hooked posterior process. Paired, ventrally located vomers constitute the encasing of the Jacobson’s organ; vomers have a fontanelle between their premaxillary processes and a lateral embayment between them and the maxillae.

Palatomaxillary arch: Paired maxillae bearing 33–34 teeth; maxilla has an alveolar shelf and a shark fin-shaped facial process with an anterior embayment for the nostril and a posterior dorsal process. Anterior end of maxilla bifurcate, with an anteromedial lappet overlapping the premaxillary vomerine process; posterior end of maxilla is a tapering process articulating with ectopterygoid and jugal. Paired, edentulous, laminar palatines with slender anterolateral and anteromedial processes, the latter lodging into a notch in the vomer. Paired, edentulous, triradiate pterygoids with a wide, short palatine process, small, tapering ectopterygoid process and an elongated, caudolaterally directed quadrate process. The ectopterygoid process bears articulatory surfaces for the basipterygoid process and epipterygoid. Paired, crescentic ectopterygoids with tapering rostral and caudal ends.

Dermatocranial roofing and circumorbital elements: Single bell-shaped (in dorsal view) frontal consisting of a dorsal lamina, with a rounded anterior margin and widened posterior end, and orbital laminae joined along the midline. Paired, laminar parietals with two elongated, posterolateral processes and a tapering mid-caudal projection with lateral adductor ridges. Paired prefrontals articulating with maxillae and frontals. Paired elongated jugals resting over maxillary posterior process lateral to the ectopterygoid articulation. Paired, somewhat Y-shaped postorbitofrontals.

Chondrocranial braincase and otic region: Paired prootics house the anterior and horizontal semicircular canals; prootic projects anterodorsally into a prominent alar process, laterally into a spina prootica which is continuous with crista prootica. Paired otoccipitals form the housing of cochlea, and part of the horizontal and posterior semicircular canals; otoccipital projects posterolaterally into a paroccipital process. Below the fenestra ovalis, there is the lateral opening of the recessus scalae tympani, separated from the former by crista interfenestralis. Single, dorsal supraoccipital housing part of the posterior semicircular canal. Supraoccipital medially underlapped by parietal’s mid-caudal projection. Behind the underlapping articulation, a strong crest for spinalis and semispinalis muscle insertion. Single, ventral parabasisphenoid bearing the sella turcica and dorsum sellae on its dorsal surface; parabasisphenoid projects anteroventrally and laterally into basipterygoid processes. Single, ventral basioccipital forming the occipital condyle along with otoccipitals; basioccipital bears a prominent ventrolateral crest below the lateral opening of the recessus scalae tympani.

Suspensorial and palatoquadrate arch elements: Paired, J-shaped squamosals articulating parietal posterolateral process, otoccipital paroccipital process and the quadrate. Paired quadrates consisting of a cephalic condyle, posteriorly concave central column and a bicipital mandibular condyle. Paired, slender, rod-like epipterygoid.

Mandible: Paired compound bones that are an amalgam of medial prearticular, lateral surangular and posterior articular; there is an adductor fossa bounded by prearticular and surangular crests of which the lateral is higher; posteriorly projecting retroarticular process. Paired, triradiate coronoids with a triangular dorsal projection. Paired splenials. Paired, elongated dentary bearing 32 teeth.

External morphological variation. Main morphometric and meristic characters of the type series are provided in Table 1 View TABLE 1 . Morphological characters of the paratypes agree in most respects with the holotype. All paratypes show a rostral divided dorsally by a median cleft of half or less of the rostral height, but contrary to the holotype, the cleft is not prolonged by a small hexagonal scale. Similarly to all other species of Dixonius , there are no femoral pores in either sex, and precloacal pores are absent in females ( Figures 3 View FIGURE 3 and 4 View FIGURE 4 ). The dorsal pattern and color do not seem to show sexual dimorphism. Only two of the types have a complete, original tail. One is the largest adult female, RBINS 2747 About RBINS , and shows a TailL/SVL ratio of 1.09. The other, the juvenile RBINS 2752 About RBINS , shows a TailL/SVL ratio of 0.95. These two specimens respectively show 57 and 59 SC. The complete tail of RBINS 2747 About RBINS shows irregular black spots throughout its length, but no regularly spaced rings. In life, the single subadult in the type series has a uniformly blackish brown dorsal surface without any pattern ( Figure 5A View FIGURE 5 ). The two juveniles had blackish brown dorsal and ventral surfaces, with a few, irregularly disposed, white dots on the upper flanks and on the tail ( Figures 5G and 5H View FIGURE 5 ).

DNA analyses. DNA fragments of 698 and 208 base pairs (bp) of the NADH dehydrogenase subunit 2 (ND2) gene were obtained for RBINS 2749 and RBINS 2750, respectively. Since the chromatograms obtained with the primer CO1R1 were persistently unreadable, each sequence was obtained from the consensus of the independent sequencing (using primer MetF1) of two separate PCR products. The 208 characters obtained for RBINS 2750 were identical to their homologous characters in RBINS 2749. From the 37 ND2 sequences labelled as Dixonius already available in GenBank, we excluded HQ646374 View Materials , which showed a similarity ≥99.7% with records from Heteronotia binoei (Gray) , EU054298 View Materials , which originates from the same specimen as KP979732 View Materials ), and EU054297 View Materials , which was responsible for 37 singletons (unevenly distributed in the sequence) out of the 139 singletons in the alignment of the ingroup) ( Table 2 View TABLE 2 ). Proportions of nucleotide substitutions between formally described species ranged from 3.11 to 18.97%. Dixonius sambhupura sp. nov. showed divergences ranging from 4.39 to 18.97% compared to all other Dixonius species ( Table 3 View TABLE 3 ). These interspecific distances were all larger than the intraspecific distances measured for species sequenced for more than one specimen (0–0.99%). The maximum likelihood phylogenetic tree was based on an alignment of 1041 bp. The best-fit substitution models determined by IQ-TREE for the partitions corresponding to the positions 1, 2 and 3 in the codons were TVM+F+G4, HKY+F+G4 and TPM2+F+I+G4, respectively. In this tree, Dixonius sambhupura sp. nov. is a sister taxon of D. cf. siamensis (accession numbers KP979732 View Materials and EU054299 View Materials in GenBank) from Phnom Aural, Purset Province, Cambodia ( Figure 7 View FIGURE 7 ), and belongs to a lineage including D. somchanhae . In Table 2 View TABLE 2 and Figure 7 View FIGURE 7 , MT468896 View Materials , EU054299 View Materials and KP979732 View Materials , originally labelled in GenBank as Dixonius siamensis , were provisionally relabelled as D. cf. siamensis , because they originate from areas distant from the type locality and likely represent two other species ( Pauwels et al. 2024); and HM997153 View Materials , identified in GenBank as D. melanostictus , was changed to D. cf. melanostictus because its geographical origin within Thailand is unknown.

Distribution and natural history. The type series was found active at night on the ground in cultivated fields or among secondary vegetation near the Mekong River in Kratie Province ( Figures 8–10 View FIGURE 8 View FIGURE 9 View FIGURE 10 ). The type locality lies within the Prek Prasab Wildlife Sanctuary, an area protected since 2018, of critical importance for the conservation of the endangered Hog Deer, Axis porcinus (Zimmermann) ( Artiodactyla : Cervidae ) ( van Berkel et al. 2022). The area of the type locality is “a complex of remnant, seasonally flooded, grasslands (dominated by Sclerostachya fusca , as well as Imperata cylindrica , Sorghum propinquum and other grasses), arable fields, rice paddies, human settlements and patches of heavily degraded forest and open woodland” ( van Berkel et al. 2022; Figure 9 View FIGURE 9 ). Several paratypes were found in Sambor Wildlife Sanctuary, on Koh Klap island along the eastern bank of the Mekong River, at about 50 km N-NE of the type locality. Koh Klap is covered by semi-evergreen forest, with some selective logging, areas opened up for livestock and patches of degraded understory burnt for hunting ( Jocqué et al. 2018). At the type locality Dixonius sambhupura sp. nov. was found along with Malayemys subtrijuga (Schlegel & Müller) ( Geoemydidae ; voucher RBINS 18557), Gekko gecko (Linnaeus) , Hemidactylus frenatus Duméril & Bibron ( Gekkonidae ) and Amphiesma stolatum (Linnaeus) ( Natricidae ; voucher RBINS 18558). On Koh Klap Island it was found with Takydromus sexlineatus Daudin ( Lacertidae ; voucher RBINS 18580), Psammodynastes pulverulentus (Boie) (Psammodynastidae; voucher RBINS 18560) and Indotyphlops braminus (Daudin) ( Typhlopidae ; voucher RBINS 18561).

Etymology. The specific epithet refers to Sambhupura (in Khmer), the ancient name of the area of the charming city of Kratie, chief town of Kratie Province, northeastern Cambodia. It is a noun in apposition, invariable.

We suggest the following common names: จิ้งจกดินสัมภูปุระ (Djing-djok din Sambhupura, Thai), Sambhupura leaf-toed gecko (English) , and Dixonius de Sambhupura (French).

Comparison to other species. The main diagnostic morphological and chromatic characters of Dixonius species are presented in Table 4 View TABLE 4 . Dixonius sambhupura sp. nov. is readily distinguished from the southern Vietnamese D. aaronbaueri Ngo & Ziegler, 2009 by its distinctly higher SVL (49.0 versus 38.6 mm), distinctly higher Ven (24–27 versus 18 or 19), higher DTR (14 or 16 versus 11), distinctly lower PV (34–37 versus 45–50) and lower PV’ (23–25 versus 29–32), higher PrePo (6 versus 5), its lack (versus presence) of a marked canthal stripe, its spotted (versus uniform) dorsal pattern, the presence (versus absence) of WD, and the lack (versus possession) of an orange tail; from the western Thai D. chotjuckdikuli Donbundit, Sumontha, Suthanthangjai, Suthanthangjai & Pauwels, 2024 by a distinctly higher Ven (24–27 versus 16 or 18), lower DTR (14 or 16 versus 18, rarely 16), generally higher PV (34–37 versus 31–34), lower SubLT4 (12–14 versus 15–17), higher InterOrbS (9 or 10 versus 6–8), strongly barred (versus not barred) upper lips, absence (versus presence) of a marked canthal stripe, and the lack (versus possession) of an orange tail; from the southern Thai D. dulayaphitakorum Sumontha & Pauwels, 2020 by a higher Ven (24–27 versus 22) and a much lower DTR (14 or 16 versus 22). Moreover, the female paratype RBINS 2747 of Dixonius sambhupura sp. nov. has a TailL/SVL ratio of 1.09, while the three female paratypes of D. dulayaphitakorum with a complete, original tail showed ratios between 1.27 and 1.39 ( Donbundit et al. 2024), thus a proportionally longer tail.

Dixonius sambhupura sp. nov. can be separated from the central Vietnamese D. fulbrighti Luu, Grismer, Hoang, Murdoch & Grismer, 2023 View in CoL by a generally higher Ven (24–27 versus 22–24), generally lower DTR (14 or 16 versus 16–20), strongly barred (versus not barred) upper lips, and the absence (versus presence) of a marked canthal stripe. The only adult female paratype of Dixonius fulbrighti View in CoL with a complete, original tail shows a TailL/SVL ratio of 1.43 (versus 1.09 in D. sambhupura sp. nov.), i.e., a distinctly longer tail. Dixonius sambhupura sp. nov. differs from the central Vietnamese D. gialaiensis Luu, Nguyen, Le, Grismer, Ha, Sitthivong, Hoang & Grismer, 2023 View in CoL by a higher Ven (24–27 versus 19–21), lower DTR (14 or 16 versus 19), higher InterOrbS (9 or 10 versus 7), lower PrePo (6 versus 7 or 8), and absence (versus presence) of a marked canthal stripe; from the western Thai D. hangseesom Bauer, Sumontha, Grossmann, Pauwels & Vogel, 2004 View in CoL by a distinctly higher SVL (49.0 versus 42.1 mm), lower IL (6 or 7 versus 8), absence (versus presence) of a marked canthal stripe, and the lack (versus possession) of an orange tail; from the northeastern Thai D. hinchangsi by its higher DTR (14 or 16 versus 12), generally higher PV (34–37 versus 30–34), and the presence (versus absence) of WD; from the peninsular Thai D. kaweesaki Sumontha, Chomngam, Phanamphon, Pawangkhanant, Viriyapanon, Thanaprayotsak & Pauwels, 2017 View in CoL by a distinctly higher SVL (49.0 versus 41.6 mm), higher DTR (14 or 16 versus 12 or 13), lower SubLT4 (12–14 versus 15), higher InterOrbS (9 or 10 versus 6 or 7), lower SL (7–9 versus 10 or 11), lower SLMOrb (6 th versus 7 th or 8 th), distinctly lower PrePo (6 versus 9–11), absence (versus presence) of a marked canthal stripe, spotted (versus striped) dorsal pattern, presence (versus absence) of WD, and lack (versus possession) of an orange tail; from the central Laotian D. lao View in CoL by a distinctly lower DTR (14 or 16 versus 20–23), lower PV (34–37 versus 40–43), lower SubLT4 (12–14 versus 15), lower SLMOrb (6 th versus 7 th or 8 th), lower PrePo (6 versus 8), strongly barred (versus not barred) upper lips, spotted or blotched (versus uniform) dorsal pattern, and presence (versus absence) of WD; from the eastern Thai D. mekongensis Pauwels, Panitvong, Kunya & Sumontha, 2021 View in CoL by a generally higher Ven (24–27 versus 22–24), generally higher PV (34–37 versus 32–34), lower PrePo (6 versus 7), and absence (versus presence) of a marked canthal stripe.

Dixonius sambhupura sp. nov. can be distinguished from the central Thai D. melanostictus View in CoL by a higher Ven (24–27 versus 22), higher DTR (14 or 16 versus 10 or 11), lower SubLT4 (12–14 versus 15), lower SLMOrb (6 th versus 7 th), lower PrePo (6 versus 9), absence (versus presence) of a marked canthal stripe, strongly barred (versus not barred) upper lips, a spotted or blotched (versus striped) dorsal pattern, and lack (versus possession) of an orange tail; from the southern Vietnamese D. minhlei Ziegler, Botov, Nguyen, Bauer, Brennan, Ngo & Nguyen, 2016 View in CoL by a higher Ven (24–27 versus 20–23), lower PV (34–37 versus 38–44), lower PrePo (6 versus 7 or 8), absence (versus presence) of a marked canthal stripe, upper lips strongly (versus not strongly) barred, and presence (versus absence) of WD; from the northern Laotian D. muangfuangensis View in CoL by a higher Ven (24–27 versus 20 or 21), distinctly lower DTR (14 or 16 versus 21–23), distinctly lower PV (34–37 versus 45–48), lower SubLT4 (12–14 versus 15), higher InterOrbS (9 or 10 versus 7), and lower PrePo (6 versus 7 or 8); from the peninsular Thai D. pawangkhananti Pauwels, Chomngam, Larsen & Sumontha, 2020 View in CoL by a distinctly higher SVL (49.0 versus 42.6 mm), distinctly higher Ven (24–27 versus 16), higher PV (34–37 versus 30–32), higher PV’ (23–25 versus 18–21), higher InterOrbS (9 or 10 versus 7), absence (versus presence) of a marked canthal stripe, and lack (versus possession) of an orange tail; from the central Thai D. siamensis View in CoL by a lower PrePo (6 versus 7), absence (versus presence) of a marked canthal stripe and presence (versus absence) of WD (if present in D. siamensis View in CoL , very poorly contrasted; Pauwels et al. 2024; from the Laotian D. somchanhae Nguyen, Luu, Sitthivong, Ngo, Nguyen, Le & Ziegler, 2021 View in CoL by a lower DTR (14 or 16 versus 19–21), higher InterOrbS (9 or 10 versus 7 or 8), and the absence (versus presence) of a marked canthal stripe; from the southern Vietnamese, insular D. taoi Botov, Phung, Nguyen, Bauer, Brennan & Ziegler, 2015 View in CoL by a higher Ven (24–27 versus 21–23), higher DTR (14 or 16 versus 11 or 12), and the absence (versus presence) of a marked canthal stripe; and from the southern Vietnamese D. vietnamensis Das, 2004 View in CoL by a distinctly higher SVL (49.0 versus 42.4 mm), higher Ven (24–27 versus 15–21), absence (versus presence) of a marked canthal stripe, and strongly (versus not strongly) barred lips. Dixonius sambhupura sp. nov. is also distinct from the Myanmar Dixonius burmanicus View in CoL by its distinctly higher SubLT4 (12 or 14 versus 8 or 9 according to the original description).

Dixonius sambhupura sp. nov. differs from D. hinchangsi in having fewer maxillary teeth (33 or 34 in the former versus 35 or 36 in the latter), and a more rounded anterior end of the frontal (versus a more tapering one in D. hinchangsi ; see Pauwels et al. 2025). Based on cranial osteology, Dixonius sambhupura sp. nov. is not distinguishable from D. siamensis View in CoL (see Pauwels et al. 2024). The cranial osteology of the other Dixonius species has not yet been studied.