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Oligodon rostralis NGUYEN, TRAN, NGUYEN, NEANG, YUSHENKO & POYARKOV, 2020

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Higher TaxaColubridae, Colubrinae, Colubroidea, Caenophidia, Alethinophidia, Serpentes, Squamata (snakes) 
Subspecies 
Common NamesE: Long-snouted kukri snake
Vietnamese: Răn khiêm mõm dài
Russian: Dlinnorylyi oligodon 
SynonymOligodon rostralis NGUYEN, TRAN, NGUYEN, NEANG, YUSHENKO & POYARKOV 2020 
DistributionS Vietnam (Lam Dong)

Type locality: Bidoup–Nui Ba National Park, ca. 6 km northwards from Da Nhim village, Da Chais Commune, Lac Duong District, Lam Dong Province, southern Vietnam (12.1518°N, 108.5279°E; elevation 1,622 m a.s.l.),  
Reproduction 
TypesHolotype. SIEZC 20201, adult male, collected on a steep slope near to mountain summit in montane evergreen pine forest by Bang Van Tran and Linh Hoang Nguyen at 23 h on June 13, 2017. 
DiagnosisDiagnosis. The new species is assigned to the genus Oligodon Fitzinger, 1826 on the basis of its phylogenetic position and the following morphological attributes: posterior maxillary teeth enlarged and compressed; head short, barely distinct from neck; eye well-developed with round pupil; rostral enlarged; body cylindrical with smooth scales; ventrals rounded; subcaudals paired. Oligodon rostralis sp. nov. is distinguished from its congeners by a combination of the following morphological characters: medium size in adults (male TL = 582 mm); head small and broad with long largely protruding snout; 15 dorsal scale rows at neck and midbody and 13 rows before vent; ventrals 167, subcaudals 47 in male; single preocular, single postocular; loreal and presubocular absent; six supralabials, third and fourth entering orbit; six infralabials, anterior four contacting chin shields; internasals separate from prefrontals; nasal divided; single anterior and two posterior temporals; cloacal plate undivided; comparatively short hemipenis, forked in anterior one third of their length, extending to 8th subcaudal, lacking spines and papillae, bearing prominent transverse flounces and distal calyces; six maxillary teeth, the posterior three being enlarged; dark temporal streak present, edged with white; 14+4 large dark-brown dorsal blotches; bright-orange vertebral stripe on tail and dorsum; and ventral surfaces in life cream with quadrangular spots.

Comparisons. By having 15-15-13 dorsal scale rows, Oligodon rostralis sp. nov. can be distinguished from other species inhabiting mainland Southeast Asia having greater number of MSR, namely all members of the O. cyclurus species group: O. cyclurus (Cantor) (19 or 21); O. formosanus (Günther) (19); O. ocellatus (Morice) (19); O. fasciolatus (Günther) (21 or 23); O. kheriensis Achraji & Ray (19); O. juglandifer (Wall) (19); O. chinensis (Günther) (17); O. saintgironsi David, Vogel & Pauwels (17 or 18); O. culaochamensis Nguyen, Nguyen, Nguyen, Phan, Jiang & Murphy (17); O. condaoensis Nguyen, Nguyen, Le & Murphy (17); O. macrurus (Angel) (17); O. arenarius Vassilieva (17) and O. cattienensis Vassilieva, Geissler, Galoyan, Poyarkov, Van Devender & Böhme (17); phylogenetic position of the latter two species is unclear. Similarly, by having 15 MSR the new species can be diagnosed from the members of the O. taeniatus species group: O. taeniatus (Günther) (19); O. barroni (Smith) (17); O. mouhoti (Boulenger) (17); O. pseudotaeniatus David, Vogel & Van Rooijen (17); O. moricei David, Vogel & Van Rooijen (17) and O. deuvei David, Vogel & Van Rooijen (17). Most members of the O. cinereus species group, which all are believed to have an unforked hemipenis (vs. bilobed hemipenis in the new species; see Green, Orlov & Murphy, 2010), can be also distinguished from Oligodon rostralis sp. nov. by larger MSR: O. cinereus (Günther) (17); O. nagao David, Nguyen, Nguyen, Jiang, Chen, Teynié & Ziegler (17); O. joynsoni (Smith) (17); O. saiyok Sumontha, Kunya, Dangsri & Pauwels (17); O. huahin Pauwels, Larsen, Suthanthangjai, David & Sumontha (17), and O. albocinctus (Cantor) (19 or 21); another member of the O. cinereus species group –O. inornatus (Boulenger) has 15 MSR and is compared with the new species below. Diagnostics of Oligodon rostralis sp. nov. from other mainland Southeast Asian species of Oligodon with 15 or 13 dorsal scale rows appear to be the most pertinent (as the number of MSR may vary between these two values due to the position of the dorsal scale row reduction, see David et al., 2012); it is summarized in Table 5. From most species with 15 or 13 MSR, the new species can be distinguished by absence of loreal vs. loreal present in O. eberhardti Pellegrin; O. inornatus; O. kampucheaensis Neang, Grismer & Daltry; O. jintakunei Pauwels, Wallach, David, Chanhome (vestigial loreal); O. planiceps (Boulenger); O. torquatus (Boulenger); O. dorsalis (Gray) and O. melaneus Wall (vestigial loreal). By presence of an entire cloacal plate Oligodon rostralis sp. nov. can be diagnosed from those species who have the cloacal plate divided, namely from O. catenatus (Blyth), O. eberhardti, O. lacroixi Angel & Bourret, O. jintakunei, O. lungshenensis Zheng & Huang, O. ornatus Van Denburgh, O. hamptoni Boulenger, O. mcdougalli Wall, O. planiceps, O. torquatus, O. dorsalis, O. melaneus, and O. erythrorhachis Wall. By having internasals separate from prefrontals the new species can be readily diagnosed from those Oligodon species which have these scales fused, including O. catenatus, O. eberhardti, O. lacroixi, O. jintakunei, O. brevicauda and O. hamptoni. By having a single postocular scale Oligodon rostralis sp. nov. is distinguished from those species which have two postocular scales: O. catenatus, O. lacroixi, O. inornatus, O. kampucheaensis, O. lungshenensis, O. hamptoni, O. planiceps, O. torquatus, O. melaneus, O. brevicauda and O. erythrorhachis. The new species can be further distinguished from O. brevicauda by having a single preocular scale (vs. 2 preoculars). By having six supralabials the new species can be distinguished from Oligodon species with five (O. lacroixi, O. hamptoni, and O. planiceps), seven (O. jintakunei, O. mcdougalli, O. torquatus, O. dorsalis, O. melaneus, O. brevicauda and O. erythrorhachis), or eight (O. inornatus and O. kampucheaensis) supralabials. Among all congeners Oligodon rostralis sp. nov. morphologically is most similar to O. annamensis, to which this species is also most closely related phylogenetically (see Results). However, the new species can be distinguished from males of O. annamensis by the following combination of morphological characters: (1) greater number of dorsal scale rows, DSR formula 15-15-13 (vs. DSR formula 13-13-13 in O. annamensis); (2) hemipenis bilobed, lobes bifurcating at distal third of body with flounces and lacking papillae (vs. hemipenis bilobed and elongate, lobes bifurcating proximally with papillae and transverse ridges in O. annamensis), (3) nasal vertically divided (vs. nasal entire in O. annamensis); (4) generally larger total length, 582 mm (vs. maximal total length 412 mm in O. annamensis); (5) generally wider head, HW/HL ratio 73.2% (vs. HW/HL ratio 53.6–56.3% in O. annamensis males, and 61.7% in female holotype; see Table 4); (6) generally higher number of subcaudals, 47 (vs. 30–46 in O. annamensis); (7) dorsal pattern consisting of large dark butterfly-shaped blotches and a light middorsal orange stripe (vs. white narrow crossbars edged with black and no middorsal stripe in O. annamensis); (8) ventral color in life cream-white with black quadrangular spots not forming transverse bars (vs. ventral surfaces in life bright coral-red to bright orange with black quadrangular spots forming transverse bars in O. annamensis) (see Tables 4 and 5). Finally, the new species is distinguished from O. annamensis by a significant divergence in mtDNA gene sequences (up to 3.3% of substitutions in 16S rRNA gene, see Table 3). 
CommentHAbitat: The type specimen was collected on the steep slope close to the mountain summit, at late night (23 h). The animal was found on ground in leaf litter on the edge of the mixed-pine forest (dominated by Pinus keysia Royle ex Gordon) and evergreen montane broadleaf forest (dominated with trees of the families Fabaceae, Fagaceae, and few large pine trees of Pinus keysia, with understory consisting mostly of Poaceae –different species of bamboo).

Sympatry: Cyrtodactylus bidoupimontis, Scincella rufocaudata, Pareas hamptoni.

Phylogenetic position. Oligodon rostralis sp. nov. is a sister species of O. annamensis, from which it is genetically divergent with p-distance 3.3% in 16S rRNA gene. 
EtymologyThe specific name ‘‘rostralis’’ is a Latin adjective in the nominative singular, masculine gender, derived from Latin words ‘‘rostrum’’ for ‘‘snout’’ or ‘‘beak’’ in reference to protruding snout distinctive for the new species. 
References
  • Nguyen HN, Tran BV, Nguyen LH, Neang T, Yushchenko PV, Poyarkov NA. 2020. A new species of Oligodon Fitzinger, 1826 from the Langbian Plateau, southern Vietnam, with additional information on Oligodon annamensis Leviton, 1953 (Squamata: Colubridae). PeerJ 8: e8332 - get paper here
 
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