Dixonius chotjuckdikuli sp. nov.

(Figures 1–7)

Holotype. CUMZ-R-2619 (field no. MS 646); adult male from Khao Ebid (Mount Ibit; 13°20’08.5”N 99°45’17.3”E), Khao Yoi District, Phetchaburi Province, western Thailand, collected by Natthaphat Chotjuckdikul, Nattasuda Donbundit, Montri Sumontha, Winai Suthanthangjai, and Sudjidtra Wattanakij on 12 November 2023.

Paratypes. CUMZ-R-2614 (field no. MS 641) and CUMZ-R-2615 (field no. MS 642), adult males; CUMZ-R-2616 (field no. MS 643), adult female, CUMZ-R-2617 (field no. MS 644), adult female; and CUMZ-R-2618 (field no. MS 645), subadult female. All five paratypes collected on 6 October 2023 by the same collectors and at the same locality as the holotype.

Diagnosis. Dixonius chotjuckdikuli sp. nov. can be distinguished from all other congeneric species by the combination of its maximal known SVL of 45.6 mm; 18 (rarely 16) longitudinal rows of dorsal tubercles; 31 to 34 paravertebral scales; 18 (rarely 16) longitudinal rows of ventrals across the abdomen; 20 to 22 interciliary scales; five or six precloacal pores in males, no pores in females; a marked canthal stripe extending beyond the shoulder; and a blotched dorsal pattern in males, females and juveniles.

Description of holotype. Adult male (Figures 1–3). SVL 43.3 mm. Head relatively long (HL/SVL ratio 0.30), wide (HW/HL ratio 0.66), not markedly depressed (HD/HL ratio 0.44), distinct from neck. Lores and interorbital region weakly inflated. Canthus rostralis relatively prominent. Snout moderately short (SnOrb/HL ratio 0.36), rounded, longer than orbit diameter (OrbD/SnOrb ratio 0.66). Scales on snout and forehead small, hexagonal to rounded, flattened, with smooth or slightly rugose surface. Scales on snout slightly larger than those on occipital region. Eye of moderate size (OrbD/HL ratio 0.24). Pupil vertical with crenelated margins. Supraciliaries short, without spines. Ear opening oval, small (EarL/HL ratio 0.04); orbit to ear distance greater than orbit diameter. Rostral about twice wider than high, dorsally incompletely divided by a median cleft. Two enlarged supranasals in broad contact. Rostral in contact with supralabial I on each side, nostrils and both supranasals. Nostrils round, each surrounded by supranasal, rostral, supralabial I and two postnasals. Mental triangular, about as long as deep. Two pairs of enlarged postmentals, anteriormost approximately five times larger than posterior. Each anterior postmental bordered anteriorly by mental, medially by the other anterior postmental, anterolaterally by infralabial I, posterolaterally by the second postmental; the pair of postmentals collectively bordered posteromedially by a row of five throat scales. Supralabials to mid-orbital position 6/7; enlarged supralabials to angle of jaws 8/8. Infralabials 6/6. Interorbital scales 8.

Body slender, elongate (TrunkL/SVL ratio 0.43), without ventrolateral folds. Dorsal scales small, irregular, flattened to conical, distributed among large, strongly keeled tubercles arranged in 18 regular longitudinal rows at midbody. Lower flanks covered with irregular, smooth to slightly conical 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 venter to lowest rows of tubercles 18. Six precloacal pores in a continuous series. Pore-bearing scales not enlarged relative to adjacent scale rows. No femoral pores or enlarged femoral scales.

Fore- and hind limbs short, slender (FAL/SVL ratio 0.14; TibL/SVL ratio 0.15). Digits slender, dilated distally, all bearing robust, slightly recurved claws. Basal subdigital lamellae narrow, without scansorial surfaces (6-9-11- 10-9 right manus; 6-8-13-17-12 right pes); setae-bearing lamellae restricted to enlarged, distal, ‘‘leaf-like’’ scansors. Scales on palm and sole small, smooth, rounded to oval. Interdigital webbing absent. Relative length of digits: IV=III>II>V>I (manus), IV>V>III>II>I (pes). Tail length 59.7 mm; tail original. Supracaudals markedly keeled in the anterior portion of the tail. Subcaudals 52, enlarged into transverse plates.

Coloration in life. Dorsal surface of head light brown with small and irregular black blotches. Supraciliaries and numerous scales on dorsal surface of the head golden yellow. Supraorbital area bluish. The supralabials and infralabials are off-white, and do not show black vertical bars. On each side of the head a black canthal stripe runs from the nostril through the eye and the ear and is prolonged by a wavy stripe on the upper flanks which extends posteriorly till above the cloaca. Dorsum light brown with black blotches. The four paravertebral rows of tubercles are well separated and darker than the areas separating them, forming four contrasting mediodorsal dark lines. Irregularly disposed golden yellow tubercles lie on this stripe as well on the black areas of the dorsum. Dorsal surfaces of members light brown with scattered small black spots and golden yellow tubercles. Tail golden yellow. Throat, lower flanks, venter and underside of limbs white. In preservative the colors strongly fade and become less contrasted; the golden yellow color disappears and becomes light grey (Figures 2 and 3).

Variation. Main morphometric and meristic characters of the type series are provided in Table 1. Morphological characters of the paratypes agree in most respects with the holotype. Similarly to the holotype, the male paratypes have a continuous series of pores. Precloacal pores are absent in females. The dorsum, venter and underside of tail are distinctly darker in females than in males. The only type with a complete original tail, the holotype, shows a TailL/SVL ratio of 1.38. All three female paratypes have an original tail; their TailL/SVL ratio varies between 1.27 and 1.39. The underside of the regenerated part of the tail in the two male paratypes is covered with small, irregular scales, not transversely enlarged.

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*partly regenerated.

Distribution and natural history. Khao Ebid is an abruptly rising, isolated hill of Permian limestone surrounded by a flat, densely cultivated area (Figure 9). It is about 4.5 km long, about 1 km wide, and shows several peaks, the highest reaching 359 m asl (Fontaine et al. 2012). The type-locality is only at 400 m from the border with Ratchaburi Province.

The types and other individuals were found active between 11 PM and midnight on limestone boulders among shrubs (Figure 10). Some individuals were found on a concrete building, and others in the entrance of Tham Bo (a cave from which a single vertebrate, the bat Taphozous melanopogon Temminck, has been recorded so far, cf. Jantarit & Ellis 2023). We photographed a subadult individual feeding on a cricket (Grylloidea) (Figure 5). Amphibians and reptiles found in syntopy with the new species include the anurans Duttaphrynus melanostictus (Schneider) (Anura: Bufonidae), Kaloula pulchra Gray (Anura: Microhylidae), and the squamates Cyrtodactylus sp., Dixonius cf. siamensis, Gehyra fehlmanni (Taylor), Hemidactylus frenatus Duméril & Bibron and H. platyurus (Schneider) (Squamata: Gekkonidae), and Lycodon capucinus Boie (Squamata: Colubridae).

CUMZ-R-2616 and CUMZ-R-2617, showing SVL of 44.8 mm and 43.2 mm, respectively, both collected in early October, contain each two eggs at an advanced stage of development (visible on Figure 3B).

Etymology. The specific epithet honors the Thai petroleum engineer, keen naturalist and birdwatcher Natthaphat Chotjuckdikul, a companion in herpetological expeditions, who co-discovered the species described here. We suggest the following common names: จิ้งจกดินเขาอีบิด (Djing-djok din Khao Ebid, Thai), Khao Ebid leaf-toed gecko (English), and Dixonius de Khao Ebid (French).

Comparison to other species. The main diagnostic morphological and chromatical characters of Dixonius species are presented in Table 2. Based on its low number of Ven (18, rarely 16), Dixonius chotjuckdikuli sp. nov. is distinguished from D. dulayaphitakorum Sumontha & Pauwels, 2020 (22 Ven), D. fulbrighti Luu, Grismer, Hoang, Murdoch & Grismer, 2023 (22–24), D. gialaiensis Luu, Nguyen, Le, Grismer, Ha, Sitthivong, Hoang & Grismer, 2023 (19–21), D. hangseesom Bauer, Sumontha, Grossmann, Pauwels & Vogel, 2004 (22–26), D. kaweesaki Sumontha, Chomngam, Phanamphon, Pawangkhanant, Viriyapanon, Thanaprayotsak & Pauwels, 2017 (24), D. lao Nguyen, Sitthivong, Ngo, Luu, Nguyen, Le & Ziegler, 2020 (23 or 24), D. mekongensis Pauwels, Panitvong, Kunya & Sumontha, 2021 (22–24), D. melanostictus (22), D. minhlei Ziegler, Botov, Nguyen, Bauer, Brennan, Ngo & Nguyen, 2016 (20–23), D. muangfuangensis Luu, Nguyen, Le, Grismer, Ha, Sitthivong, Hoang & Grismer, 2023 (20 or 21), D. somchanhae Nguyen, Luu, Sitthivong, Ngo, Nguyen, Le & Ziegler, 2021 (23–26) and D. taoi Botov, Phung, Nguyen, Bauer, Brennan & Ziegler, 2015 (21–23). The DTR number of Dixonius chotjuckdikuli sp. nov. (18, rarely 16) separates it from D. aaronbaueri (11), D. dulayaphitakorum (22), D. gialaiensis (19), D. hangseesom (12–14), D. kaweesaki (12 or 13), D. lao (20–23), D. melanostictus (10 or 11), D. minhlei (14 or 15), D. muangfuangensis (21–23), D. siamensis (10–14), D. somchanhae (19–21), and D. taoi (11 or 12). Its PV number (31–34) distinguishes Dixonius chotjuckdikuli sp. nov. from D. aaronbaueri (45–50), D. lao (40–43), D. minhlei (38–44), D. muangfuangensis (45–48), D. somchanhae (35–40) and D. vietnamensis (36). Its blotched dorsal pattern separates Dixonius chotjuckdikuli sp. nov. from all currently recognized species but D. hangseesom, D. pawangkhananti and D. taoi. Dixonius chotjuckdikuli sp. nov. is also distinct from Phyllodactylus burmanicus Annandale, 1905 (described and known only from Dawei in Myanmar and currently regarded as a synonym of Dixonius siamensis but probably distinct based on zoogeography), by the possession of 18 (rarely 16) DTR (versus 12), 7 or 8, rarely 9, SL (versus 6), and 5 or 6 PrePo (versus 7).

The possession of a yellow or orange tail by Dixonius chotjuckdikuli sp. nov. is shared with male and female D. aaronbaueri, with D. hangseesom, with male and female D. kaweesaki, D. melanostictus and with adult D. pawangkhananti. Morphologically and chromatically, the two species most closely related to Dixonius chotjuckdikuli sp. nov. are D. hangseesom and D. pawangkhananti. From both species, Dixonius chotjuckdikuli sp. nov. is readily recognizable by the wide separation of its paravertebral rows (Figure 7), which show at least two granule rows between them, versus none or one in D. hangseesom and D. pawangkhananti. In addition to differences noted above, from Dixonius hangseesom, D. chotjuckdikuli sp. nov. differs by its lower InterOrbS number (8, rarely 6, versus 10), and lips whitish in adults (versus strongly barred with black). From Dixonius pawangkhananti, D. chotjuckdikuli sp. nov. can also be distinguished by its lower ICS number (20–22 versus 24–26), and its generally higher Ven number (18, rarely 16, versus 16) and higher DTR (18, rarely 16, versus 16), and its non-barred (versus barred) lips. The color and pattern of juvenile Dixonius chotjuckdikuli sp. nov. are moreover very different from those of juvenile D. pawangkhananti (dorsum black with large light brown patches and orange tail versus dorsum and tail dark grey with black spots; compare our Figure 6 with Figure 5 A–B in Pauwels et al. 2020). The striking sexual dimorphism in dorsal pattern observed in Dixonius pawangkhananti (banded in males, blotched in females) is not observed in D. chotjuckdikuli sp. nov.