﻿Southbound – the southernmost record of Tylototriton (Amphibia, Caudata, Salamandridae) from the Central Highlands of Vietnam represents a new species

﻿Abstract A new species of the genus Tylototriton is described from Ngoc Linh Mountain, Kon Tum Province, in the Central Highlands of Vietnam based on integrative taxonomy, namely by combining molecular and morphological evidence. Tylototritonngoclinhensissp. nov. differs from all other congeners based on morphological data, allopatric distribution, and molecular divergence. In terms of genetic divergence, Tylototritonngoclinhensissp. nov. distinctly differs from the sister species T.panhai (6.77%) and from T.ngarsuensis (12.36%) based on the mitochondrial NADH dehydrogenase subunit 2 (ND2) gene. Tylototritonngoclinhensissp. nov. is a moderate sized and robust salamander species with large cephalic edges, parotoids, and vertebral ridge orange in coloration. The new taxon differs from its congeners by a combination of the following morphological characteristics: size medium (SVL 60.8–66.5 mm, TL 57.6–61.8 mm in males, and SVL 72.5–75.6 mm, TL 62.9–67.9 mm in females); head longer than wide; parotoids very prominent and enlarged, projecting backwards; tail length shorter than snout-vent length; vertebral ridge large, high and glandular in appearance; 14 large and distinct dorsolateral glandular warts; gular fold present; tips of fore and hind limbs overlapping when adpressed along the body; tips of fingers reaching between eye and nostril when foreleg is laid forward; dorsal surface and lateral sides of the head, upper and lower lips, dorsolateral glandular warts, vertebral ridge, the peripheral area of the cloaca and the ventral edge of the tail orange in coloration; the presence of a distinct black line extending from the posterior end of the eye towards the shoulder. Tylototritonngoclinhensissp. nov. is restricted to evergreen montane forests near water bodies on Ngoc Linh Mountain. We suggest that the new species should be classified as Endangered (EN) in the IUCN Red List. This new important discovery represents the eighth Tylototriton taxon described from Vietnam, and at the same time constitutes the southernmost distributional record for the whole genus in Asia.


Introduction
The salamandrid genus Tylototriton Anderson, 1871, commonly known as crocodile newts, currently contains 38 species inhabiting montane forest areas throughout the Asian monsoon climate zone and is distributed across Asia, from eastern Himalayas, eastern Nepal, northern India, Bhutan, Myanmar, central to southern China (including Hainan Island), and southwards through Laos, Thailand, and Vietnam (Dufresnes and Hernandez 2022;Li et al. 2022;Wang et al. 2022;Frost 2023).
Remarkably, 15 new species have been described in the past five years (Hernandez 2016; Dufresnes and Hernandez 2022;Frost 2023).The genus was subdivided into three subgenera, Tylototriton, Yaotriton, and Liangshantriton (e.g., Dubois and Raffaëlli 2009;Nishikawa et al. 2013a;Bernardes et al. 2020;Pomchote et al. 2021) and includes several, as yet, unnamed taxa, which contain cryptic species that are morphologically difficult to distinguish, especially in their southern range of distribution (Hernandez 2016;Pomchote et al. 2021;Poyarkov et al. 2021b).Most of the new discoveries derived from the splitting of widely distributed Tylototriton taxa through the efforts of integrative taxonomy, namely the combination of morphological and phylogenetic analyses.
During recent fieldwork in May 2022 a new Tylototriton population was discovered in Ngoc Linh Mountain, Kon Tum Province, Central Vietnam resembling the T. panhai phenotype I from Phu Luang Wildlife Sanctuary and Phu Ruea National Park, Loei Province, northeastern Thailand (see Hernandez 2016;Hernandez and Pomchote 2020).However, morphological comparisons and molecular phylogenetic analyses revealed this southernmost Tylototriton population to be distinct from all related species of the genus.We herein describe the newly discovered Tylototriton population from the Central Highlands of Vietnam as a new species.

Sampling
A field survey was conducted in Ngoc Linh Nature Reserve, Kon Tum Province of the Central Highlands, Vietnam, on 22 nd of May 2022.Crocodile newts were found on the forest floor between 9:00 and 16:00.After having been photographed in ZooKeys 1168ZooKeys : 193-218 (2023)), DOI: 10.3897/zookeys.1168.96091Trung My Phung et al.: Southbound -Southernmost record of Tylototriton represents a new species life, six specimens were anaesthetized and euthanized in a closed vessel with a piece of cotton wool containing ethyl acetate (Simmons 2002), fixed in 80% ethanol for five hours, and then later transferred to 70% ethanol for permanent storage.Muscle tissue from the central upper part of the tail was taken for tissue samples, which were preserved separately in 70% ethanol prior to fixation.Voucher specimens referred to in this paper were deposited in the collections of the Institute of Ecology and Biological Resources (IEBR), Hanoi, Vietnam.
For the phylogenetic analyses, 53 sequences of species of the genus Tylototriton were used in combination with a sequence of Pleurodeles waltl and Echinotriton chinhaiensis as outgroups according to Li et al. (2022) (Table 1).
CHROMAS PRO software (Technelysium Pty Ltd., Tewantin, Australia) was used to edit the sequences, which were aligned using MAFFT v. 7 (Katoh and Standley 2013) with default settings.We then checked the initial alignments by eye and adjusted them slightly.Phylogenetic trees were constructed by using maximum likelihood ML) and Bayesian inference (BI).Prior to ML and Bayesian analyses, we chose the optimum substitution models for entire sequences using KAKUSAN 4 (Tanabe 2011) based on the Akaike information criterion (AIC).The best model selected for ML and BI was the general time-reversible model (GTR : Tavaré 1986) with a gamma shape parameter (G: 0.337 in ML and 0.376 in BI).For ML analysis, the TREEFINDER software (Jobb et al. 2004) was used while BI analysis was conducted using MRBAYES v. 3.2.7a(Ronquist et al. 2012).The strength of nodal support in the ML tree was analyzed using non-parametric bootstrapping (MLBS) with 1,000 replicates.We regarded tree nodes in the ML tree with bootstrap values of 75% or greater as sufficiently resolved (Hillis and Bull 1993), and nodes with a BPP of 95% or greater as significant in the BI analysis (Leaché and Reeder 2002).The BI summarized two independent runs of four Markov Chains for 10,000,000 generations.A tree was sampled every 100 generations and a consensus topology was calculated for 70,000 trees after discarding the first 30,001 trees (burn-in 1,000,000).We checked parameter estimates and convergence using TRACER v. 1.6 (Rambaut and Drummond 2013).Pairwise comparisons of uncorrected sequence divergences (p-distance) were calculated with MEGA 7 (Kumar et al. 2016) for ND2 fragments only between species of the genus Tylototriton.Variance was estimated using bootstrap method with 1,000 replicates using nucleotide substitution while gap/missing data were treated via pairwise deletion.

Phylogenetic analyses
Aligned, combined sequences yielded a total of 1,035 characters.Of 1,035 nucleotide sites, 416 were variable and 336 were parsimony informative within the in-group.The ML and Bayesian analyses produced topologies with -lnL = 7442.0236and 7521.862,respectively.Phylogenetic analyses employing ML and BI methods yielded slightly different topologies only among referenced species, and only the ML tree is presented in Fig. 1.
Monophyly of Tylototriton with respect to the outgroup species was fully supported (each 100% support in ML bootstrap value and Bayesian posterior probability) and samples were split into four major clades named A, B, C, and D.
The Tylototriton population from Kon Tum Provice, Vietnam exhibited distinct genetic distances from the thirty-three examined species of Tylototriton, with uncorrected p-distance of 6.77% (compared to T. panhai from Laos) to 12.36% (compared to T. ngarsuensis), being higher than that between some pairs of sister species, for example, T. verrucosus vs T. shanjing (1.16%), and T. maolanensis vs T. tongziensis (2.42%).
Furthermore, the population of Tylototriton sp. from Kon Tum Province, Vietnam was also clearly separated morphologically from all the other congeners, including its sister species T. panhai, which is in congruence with the genetic separation.Thus, we describe the new Tylototriton population from Kon Tum Province, Vietnam as a new species.Etymology.The specific epithet ngoclinhensis refers to the type locality of the new species, Ngoc Linh Mountain in the Central Highlands of Vietnam.As common names, we suggest Ngoc Linh Crocodile Newt (English), Cá cóc sần ngọc linh (Vietnamese).
Diagnosis.The new species is assigned to the genus Tylototriton and the subgenus Yaotriton based on the results of the molecular phylogenetic analyses and the following combination of morphological attributes: rough skin covered with fine warts, the presence of dorsolateral bony ridges on the head; the presence of dorsolateral glandular warts on the body; quadrate spine absent (Nussbaum and Brodie 1982;Nishikawa et al. 2013a;Le et al. 2015).Further- more, the species is diagnosed from its congeners by the following combination of morphological characters: (1) size medium (SVL 60.8-66.5 mm, TL 57.6-61.8mm in males, and SVL 72.5-75.6 mm, TL 62.9-67.9mm in females); (2) head longer than wide; (3) parotoids very prominent and enlarged, projecting backwards; (4) tail length shorter than the snout-vent length; (5) vertebral ridge large, high, and glandular in appearance (6) 14 distinct dorsolateral glandular warts; (7) gular fold present; (8) tips of fore-and hind limbs overlapping when adpressed along the body; (9) tips of fingers reaching between eye and nostril when foreleg is laid forward; (10) dorsal surface and lateral sides of the head, upper and lower lips, rib nodules, vertebral ridge, peripheral area of the cloaca, and the ventral edge of tail with orange coloration; (11) presence of a distinct black line extending from the posterior end of the eye towards the shoulder.

Description of holotype.
A medium-sized male (SVL 66.5 mm, TL 59.5 mm).Head longer than wide (HW/HL 81.6%); head slightly concave on the top; snout short, truncate in dorsal view, slightly angular shaped in profile and protruding beyond lower jaw; nostril closer to the snout tip than to the eye; upper lip thick, fleshy and overlapping lower lip under the eye region; dorsolateral bony ridges on head prominent, moderately protruding, from above eye to above anterior end of parotoid, posterior ends relatively thick and scrolled inside; mid-dorsal ridge on head distinct and thin; parotoids enlarged, projecting backwards; tongue oval, attached to anterior floor of mouth, free laterally and posteriorly; vomerine teeth series in an inverted V-shape, converging anteriorly and reaching choanae; glandular vertebral ridge large, high, segmented tuberculate, extending from top of head to base of tail; rib nodules large, forming knob-like warts, distinctly isolated from each other, 14 on each side of body from axilla to base of tail; gular fold present.
Limbs comparatively long, and slender; length of forelimbs approximately equal to hind limbs; relative length of forelimb FORE/SVL ratio 39.0%, relative length of hind limb HIND/SVL ratio 38.1%; tips of forelimb and hind limb overlapping when adpressed along the body; tips of fingers reaching between eye and nostril when foreleg is laid forward; fingers and toes well developed, free of webbing; fingers four, comparative finger lengths 1FL<4FL<2FL<3FL; toes five, comparative toe lengths 1TL<5TL<2TL<4TL<3TL.
Tail length shorter than the snout-vent length (TL/SVL 89.5%); tail compressed laterally, the base relatively broad, tapering posteriorly, tail tip pointed; tail height less than the width at the tail base; dorsal fin fold relatively high; ventral side smooth.In general, the appearance of the tail is relatively low and flat.
Dorsal skin very rough, with small granules and larger warts on dorsal surfaces of head and dorsum, lateral sides of body and tail; ventral skin with tubercles shaped like transverse wrinkles; throat with numerous tiny flat tubercles; sur- faces of head ridges and middorsal vertebral ridge rough; limbs dorsally with numerous tiny tubercles, volar and plantar surfaces of hands and feet with tiny grooves forming reticulated pattern; flattened outer metacarpal and metatarsal tubercles distinct on palms and soles, respectively.Cloacal region slightly swollen, vent as a longitudinal slit, vent edges with numerous small transverse folds.
Coloration in life.In life, ground color of dorsal and ventral surfaces black; dorsal surface and lateral sides of head and lower lips to jaw angles, rib nodules, vertebral ridge, the peripheral area of the cloaca and the ventral edge of the tail orange; tips of fingers, toes and elbow orange-brown.
Coloration in preservative.The specimen in preservative is blackish brown.The orange coloration in life has faded to pale yellow.
Secondary sexual characteristics.Males are probably smaller than females but sample size was small (n = 3) and thus needs confirmation based on further records in the future.The female cloacal slit is short and its inner cloacal walls have no papilla.The male has papilla on its inner cloacal wall and its cloaca presents a long slit.Distribution.The new species is currently known only from the Ngoc Linh Nature Reserve, Kon Tum Province, in the Central Highlands of Vietnam (Fig. 5).
Ecological notes.All specimens were collected during the day on the forest floor, under rotten trees or under moss, near a small rocky stream (Figs 6, 7).
The surrounding habitat at the type locality of the new species in Ngoc Linh Mountain was primary montane evergreen broadleaf forest, at elevations between 1,800 and 2,300 m asl.
Morphological measurements.Morphometric measurements of Tylototriton ngoclinhensis sp.nov.examined in this study are given in Table 3.
Morphological comparisons.We compared the new species with other members of the genus Tylototriton based on data obtained from the literature (Table 4).
Tylototriton ngoclinhensis sp.nov.differs from T. anhuiensis by different shape of dorsolateral glandular warts (knob-like vs slightly flattened), the presence of orange markings on the parotoids (vs absent), the presence of orange coloration on the dorsolateral glandular warts (vs absent), and tips of fore-and hind limbs overlapping when adpressed along the body (vs meeting); from T. asperrimus by having a smaller size in females (TOL 137.7-143.5 mm vs 149.0-202.0mm), head longer than wide (vs head wider than long), the presence of orange markings on the parotoids (vs absent), and the presence of orange coloration on the dorsolateral glandular warts (vs absent); from T. broadoridgus by different shape of dorsolateral glandular warts (knob-like vs slightly flattened), the presence of orange markings on the parotoids (vs absent), the presence of orange coloration on the dorsolateral glandular warts (vs absent), and tips of fore and hind limbs overlapping when adpressed along the body (vs separated from each other); from T. dabienicus by different shape of dorsolateral glandular warts (knob-like vs slightly flattened), the presence of orange markings on the parotoids (vs absent), the presence of orange coloration on the dorsolateral glandular warts (vs absent), tips of fore-and hind limbs overlapping when adpressed along the body (vs separated from each other), and finger tips reaching between eye and nostril when foreleg is laid forward (vs reaching anterior corner of eye); from T. daloushanensis by different shape of dorsolateral glandular warts (knob-like vs slightly flattened), the presence of orange markings on the parotoids (vs absent), and the presence of orange coloration on dorsolateral glandular warts (vs absent); from T. hainanensis by having a smaller size in males .0mm vs 137.4-148.0mm), head longer than wide (vs head wider than long), different shape of dorsolateral glandular warts (knob-like vs slightly flattened), the presence of orange marking on the parotoids (vs absent), the presence of orange coloration on the dorsolateral glandular warts (vs absent), and finger tips reaching between eye and nostril when foreleg laid for-   (vs whole body dark brown but brownish tip of toes and tip of tail in some individuals); from T. liuyangensis by different shape of dorsolateral glandular warts (knob-like vs slightly flattened), the presence of orange markings on the parotoids (vs absent), the presence of orange coloration on the dorsolateral glandular warts (vs absent), tips of fore-and hind limbs overlapping when adpressed along body (vs separated from each other), and finger tips reaching between eye and nostril when foreleg laid forward (vs reaching eye); from T. lizhenchangi by having a smaller size (TOL 122.6-126.0mm vs 145.6-173.0mm in males, TOL 137.7-143.5 mm vs 150.0-156.5 mm in females), different shape of dorsolateral glandular warts (knob-like vs slightly flattened), the presence of orange coloration on the dorsolateral glandular warts (vs absent), tips of fingers reaching between eyes and nostrils when foreleg laid forward (vs reaching to tip of snout), and the presence of orange markings on the parotoids (vs absent); from T. maolanensis by having a smaller size (TOL 122.6-126.0mm vs 151.0-172.0mm in males, TOL 137.7-143.5 mm vs 142.7-170.5 mm in females), the presence of orange markings on the parotoids (vs absent), and the presence of orange coloration on the dorsolateral glandular warts (vs absent); from T. notialis by different color pattern on head and vertebral ridge (orange vs dark brown), lower lip with orange marking (vs brown), and dorsolateral glandular warts and vertebral ridge distinctively large (vs small); from T. panhai by having a different ground color (black vs dark brown to brown), the presence of a distinct black line extending from the back of the eye towards the shoulder (vs less evident brownish line to absent line), dorsal edges of tail black (vs yellow, orange to reddish brown).Since T. panhai is the closest known taxon to Tylototriton ngoclinhensis sp.nov., additional morphological comparisons were made between the two species, especially between topotypic T. panhai type I and type II from Laos.Tail height was the only character (with n ≥ 3) that showed varia-   tion, presenting higher values both in males and in females (Fig. 8) of T. panhai, in relation to the new species.The new species is distinguished from T. pasmansi by having rib nodules distinctively large (vs small), the presence of orange markings on the parotoid (vs absent), and the presence of orange colorations of the dorsolateral glandular warts (vs absent); from T. sini by different color pattern on head and vertebral ridge (orange vs dark brown), the presence of orange markings on the parotoids (vs absent), the presence of orange coloration on the dorsolateral glandular warts (vs absent), and dorsolateral glandular warts distinct and large (vs small); from T. sparreboomi by different color pattern on head and vertebral ridge (orange vs dark brown), the presence of orange markings on the parotoids (vs absent), the presence of orange coloration on the dorsolateral glandular warts (vs absent), and tips of fingers reaching between eye and nostril when foreleg laid forward (vs reaching nostril); from T. thaiorum by having head longer than wide (vs head wider than long), the presence of orange markings on the parotoids (vs absent), and the presence of orange coloration on the dorsolateral glandular warts (vs absent); from T. tongziensis by different shape of dorsolateral glandular warts (knob-like vs slightly flattened), the presence of orange markings on the parotoids (vs absent), and the presence of orange coloration on the dorsolateral glandular warts (vs absent); from T. vietnamensis by different shape of dorsolateral glandular warts (knob-like vs slightly flattened), the presence of orange markings on the parotoids (vs absent), the presence of orange coloration on the dorsolateral glandular warts (vs absent), and the presence of gular fold (vs absent); from T. wenxianensis by different shape of dorsolateral glandular warts (knob-like vs slightly flattened), the presence of orange markings on the parotoids (vs absent), the presence of orange coloration on the dorsolateral glandular warts (vs absent), and finger tips reaching to between eyes and nostrils (vs reaching nostril); from T. ziegleri by having head longer than wide (vs head wider than long), different color pattern on head and vertebral ridge (orange vs dark brown), the presence of orange markings on the parotoids (vs absent), and the presence of orange coloration on the dorsolateral glandular warts (vs absent); from T. anguliceps, T. himalayanus, T. kachinorum, T. ngarsuensis, T. panwaensis, T. phukhaensis, T. podichthys, T. pulcherrimus, T. pseudoverrucosus, T. shanorum, T. shanjing, T. uyenoi, T. umphangensis, and T. verrucosus by having limbs and tail edges dark brown except for the orange digits, palms, and soles (vs limbs and tail edges uniformly orange or pale brown in the latter), the presence of a black line extending from the back of the eye towards the shoulder (vs absent); and from T. kweichowensis and T. yangi by different color pattern on tail (black vs uniformly orange in the latter), and ventral side dark brown (vs ventrolateral sides yellow in the latter).

Discussion
New species are being continuously described within the genus Tylototriton.A total of 12 new species has been recorded during the last three years alone, from China, Thailand and northern Vietnam (Bernardes et al. 2020;Li et al. 2020;Li at al. 2022;Luo et al. 2022;Lyu et al. 2021;Pomchote et al. 2021;Poyarkov et al. 2021a;Dufresnes and Hernandez 2022;Rao 2022;Wang et al. 2022).Most recent descriptions were due to the separation of species complexes, that were previ-ously masked by phenotypic similarities (Bernardes et al. 2020;Li et al. 2020;Lyu et al. 2021;Pomchote et al. 2021;Poyarkov et al. 2021a;Luo et al. 2022).There certainly is high potential to continue uncovering new species by applying integrative taxonomic analyses (Dufresnes and Hernandez 2022).However, some novel species descriptions occur by conducting field work in previously unexplored areas.In our case, a new species was discovered in a region where several field surveys to assess the herpetological diversity had been conducted in the past (exp.Orlov 2005Orlov , 2009;;Jenkins et al. 2007;David et al. 2011).However, individuals of the new species have been only found in a recent field survey in 2022.This is also the first time that a crocodile newt species is recorded from the Central Highlands of Vietnam.Occurring at an elevation more than 1,800 m, this discovery sets an altitudinal record for the genus in the country, with former ranges distributed between 250 m (for T. vietnamensis) and 1,740 m (for T. anguliceps).Furthermore, this discovery represents the southernmost distribution range of the genus known to date.The new species is located approximately 370 air km distant from the nearest T. notialis population from Khammouan Province, Laos.Ngoc Linh Mountain is located on the northwestern border of the Kon Tum Massif and is the highest peak in Central Vietnam with 2,598 m (Sterling et al. 2006).The new species is also expected to be found in other localities on the Kon Tum Plateau.The climate in Ngoc Linh Mountain is relatively cool, as it is part of a tropical mountain system (averages of 15-18.5 °C throughout the year).Humidity is high, with strong amounts of rainfall (ranging from 2,600 to 3,200 mm per year) and distinct cloud coverage.Due to this unique climate and geographical position, Ngoc Linh has become a hotspot of amphibian diversity, with numerous endemic species.The area is also the type locality for some recently discovered species, namely Leptobrachium ngoclinhense (Orlov 2005), Theloderma nebulosum Rowley, Le, Hoang, Dau & Cao, 2011, Leptobrachella firthi (Rowley, Hoang, Dau, Le & Cao, 2012), Gracixalus lumarius Rowley, Le, Dau, Hoang & Cao, 2014, and G. trieng Rowley, Le, Hoang, Cao & Dau, 2020(Orlov 2005;Rowley et al. 2011Rowley et al. , 2012Rowley et al. , 2014Rowley et al. , 2020)).Most recently Krzikowski et al. (2022) highlighted the extraordinary endemism rate of amphibians in the Central Highlands of Vietnam, where the highest species diversity, with 130 species, was recorded among the eight regions of Vietnam while also containing the highest number of regionally occurring, micro-endemic amphibians, amounting for 26 species, for example: Leptobrachella crocea (Rowley, Hoang, Le, Dau & Cao, 2010) and Microhyla darevskii Poyarkov, Vassilieva, Orlov, Galoyan, Tran, Le, Kretova & Geissler, 2014, next to the afore-mentioned species (Krzikowski et al. 2022;Frost 2023).Thus, the discovery dealt with herein is another and very remarkable case, demonstrating that the Central Highlands play a special role in Vietnamese amphibian diversification and evolution.
Ngoc Linh Nature Reserve has been established in 1986 with an initial protected area of 41,424 hectares and represents a key biodiversity area for the threatened Golden-winged Laughingthrush, Trochalopteron ngoclinhense, listed as Endangered in the IUCN Red List, as well as for other rare species like the Truong Son Muntjac, Muntiacus truongsonensis, Rhesus Macaque, Macata mulatta, and the Stump-tailed Macaque, Macaca arctoides (Le et al. 1998;BirdLife International 2023).The Ngoc Linh Crocodile Newt certainly will represent another flagship species of this protected area and its surroundings, as individuals have been found both inside and outside of the Ngoc Linh Nature Reserve.
Together with T. panhai, T. ngoclinhensis is the only known species within the subgenus Yaotriton to present characteristic colorful markings on the body.Although there is a high phenotypic variation recorded for T. panhai (types I, II, and III from Hernandez 2016), T. ngoclinhensis is clearly distinguishable both morphologically and phylogenetically from the former.Nevertheless, further studies should be conducted to obtain additional data on population characteristics, including further biogeographical analyses.
Tylototriton species so far have been documented as having little dispersal abilities due to limitations in vagility and their specific habitat requirements (Zamudio and Wieczorek 2007).Therefore, the discovery of this new species geographically separated by more than 300 km from all known congeners, and bearing a particularly unique colorful pattern represents not only an important discovery in terms of evolution and zoogeography, but also reveals to be of high conservation relevance.

Conservation recommendation
Due to the aforementioned reasoning and given that Tylototriton ngoclinhensis sp.nov. is currently known only from Ngoc Linh Mountain, implying a limited distribution range composed of a single small isolated mountain population, is distinct evidence for a high threat potential.In addition to its special zoogeographic situation and rarity, the particular colorful appearance of the new crocodile newt species is very likely to draw the interest of illegal collectors.Therefore, this species should be provisionally considered to be listed as Endangered (EN) under IUCN Red List criteria B1ab(i,iii), as it is known only from Ngoc Linh Mountain in Kon Tum Province; the estimated extent of occurrence (EOO) is less than 500 km 2 ; and the species' habitat is currently being degraded due to human impacts, for example forest product exploitation, tourism development and agricultural cultivation.All species of the genus Tylototriton are listed in the Appendices of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES 2022) and also in the Governmental Decree No. 84/2021/ND-CP of Vietnam and therefore the new species is automatically protected under these regulations.

Figure 6 .
Figure 6.Habitat at the type locality of Tylototriton ngoclinhensis sp.nov. on Ngoc Linh Mountain.

Figure 8 .
Figure 8.Comparison of average tail heights (mm) between Tylototriton ngoclinhensis sp.nov and T. panhai.The left side shows data for males (A) of Tylototriton ngoclinhensis sp.nov.(n = 3; own data) and T. panhai (n = 15; taken from Phimmachak et al. 2015), showing 2 standard deviation (2SD) bars, which represent 95% of the population.The right side shows data for females (B) of Tylototriton ngoclinhensis sp.nov.(n = 3; own data) and T. panhai (n = 3) including two data points from Phimmachak et al. (2015), and one from Nishikawa et al. (2013a); averages marked by green horizontal lines, and ranges as vertical lines.

Table 1 .
to the nearest 0.01 mm with a digital caliper as follows: anterior ZooKeys 1168: 193-218 (2023), DOI: 10.3897/zookeys.1168.96091Trung My Phung et al.: Southbound -Southernmost record of Tylototriton represents a new species Samples of the Tylototriton species and other species used for DNA analyses in this study.

Table 2 .
Mean uncorrected (p) distance (%) among 1,035 bp fragments of ND2 of the genus Tylototriton and related taxa.