For nearly a hundred years, a modest brown snake called the Tonkin keelback has been catalogued as a single species roaming from the mountains of northern Vietnam deep into southern China. A new integrative taxonomic study, published in the journal Zoosystematics and Evolution, has now dismantled that assumption. By combining DNA sequencing with painstaking measurements of museum specimens, some of them collected in the 1930s, researchers have shown that what scientists long called Hebius atemporalis is actually two separate species. One keeps the original name; the other is entirely new to science, and it has been hiding in plain sight on the Yunnan-Guizhou Plateau of southwestern China.
The keelback genus Hebius is the most species-rich lineage within the natricid snakes, a family of mostly semi-aquatic or terrestrial serpents spread across East and Southeast Asia. These are small to medium-sized animals with elongated bodies, a weak but visible boundary between head and neck, large eyes with round pupils, and rear maxillary teeth that grow progressively larger toward the back of the jaw. Their conservatism in outward appearance, combined with considerable variation within populations, has made species-level taxonomy notoriously difficult. Recent integrative analyses that merge morphology with molecular data have repeatedly suggested that the current count of 53 recognized species, 30 of them recorded from China and 11 from Vietnam, substantially underestimates the true diversity, with numerous cryptic lineages still awaiting formal recognition.
The Tonkin keelback itself has a tangled history. René Léon Bourret described it in 1934 as Natrix atemporalis, based on three specimens from Tonkin, now northern Vietnam, and its most striking feature was the absence of temporal scales on the sides of the head, a trait almost unique among its relatives. In 1969, Edmond Malnate and John Romer examined additional material from Hong Kong and confirmed that those snakes matched Bourret’s originals from what is now Tam Dao National Park in Phu Tho Province, though no formal restriction of the type locality was ever made. The species drifted through several genus names over the decades, from Natrix to Amphiesma, until molecular phylogenetic work in 2014 settled it firmly within Hebius. Throughout all of this shuffling, the snake was reported across northern Vietnam and southern China, from Guangdong and Guangxi to Guizhou, Yunnan, Hunan, Hubei, and Chongqing, giving it the appearance of a wide-ranging generalist.
Suspicion that this apparent range concealed more than one species had been building. Earlier molecular studies had already revealed two deeply divergent clades within what was then called Hebius atemporalis, hinting that the name might be papering over real biological boundaries. The challenge was that the morphological differences between populations were subtle, sampling was limited, and no comprehensive revision had ever been attempted. To resolve the problem, the research team assembled 27 preserved specimens of the species complex, including two syntypes held at the National Museum of Natural History in Paris, and supplemented them with 12 newly collected individuals from fieldwork conducted across Vietnam and China between 2020 and 2025.
On the molecular side, the team extracted genomic DNA from muscle or liver tissue and amplified a 1,098-base-pair fragment of the mitochondrial cytochrome b gene, a standard workhorse for snake phylogenetics. Sequences were aligned and uncorrected pairwise genetic distances calculated, and the resulting dataset was analyzed with both Maximum Likelihood and Bayesian Inference methods, using 36 additional Hebius sequences and two outgroup taxa from GenBank to place the findings in context. Both approaches produced largely congruent trees. The species complex emerged as a strongly supported monophyletic group, and within it, the population from the Yunnan-Guizhou Plateau stood out as a highly divergent lineage, separated from true Hebius atemporalis by uncorrected p-distances of 8.0 to 9.8 percent. For comparison, genetic divergence within the plateau population itself was less than 1 percent, while Chinese and Vietnamese populations of the true species differed by 6.4 to 7.0 percent, a level that itself approaches thresholds commonly used to infer species-level separation in natricine snakes.
The morphological evidence proved just as decisive. The plateau snakes are larger as adults, reaching a maximum snout-vent length of 416 millimeters against 294 millimeters for true Hebius atemporalis. They have proportionally shorter tails, with the tail making up 0.22 to 0.27 of total length compared with 0.28 to 0.33 in their Vietnamese and eastern Chinese relatives. They carry more ventral scales, 146 to 156 against 123 to 140, and correspondingly higher combined ventral and subcaudal counts. Most visually striking of all, they lack the white to orangish nuchal collar that gives the Tonkin keelback its characteristic neck band, and their dorsal coloration shifts from brown to dark olive rather than from reddish brown to blackish brown. Together with the shared absence of temporal scales, these characters set the plateau population apart not only from Hebius atemporalis but from all 37 other congeners recorded in China and the Indo-Burma region.
The new species has been named Hebius malnatei, honoring Edmond V. Malnate, the American herpetologist who first revised the taxonomic placement of the Tonkin keelback. The description is anchored by an adult female holotype collected in May 2024 at Pugu Village in Panzhou County, Guizhou Province, at an elevation of 1,750 meters, with five paratypes from Yunnan and Guizhou. The species is known from across the Yunnan-Guizhou Plateau at elevations of 1,750 to 1,950 meters, inhabiting forests, shrubland, and meadows near ponds and streams. It is active by day and night, peaking around sunset, and when captured it does not bite but instead releases a strong, fetid secretion from its cloacal glands. Earthworms are the only recorded prey, and the holotype contained five well-developed oviductal eggs, indicating oviparity and a late-spring breeding season. Based on IUCN Red List criteria, the authors recommend assigning it to Least Concern, though its restricted elevational range and specialized habitat association warrant targeted surveys and long-term monitoring.
True Hebius atemporalis, meanwhile, has received a long-overdue redescription based on its syntypes and additional material. It is now confirmed from northern Vietnam, including Phu Tho, Tuyen Quang, Dien Bien, and Nghe An provinces, and from southern and central China, including Hong Kong, Guangdong, Guangxi, Guizhou, Hunan, Hubei, and Chongqing, at elevations of 400 to 1,700 meters. It is a diurnal snake of subtropical montane forests that tolerates both primary and secondary habitats, from dense evergreen shrubland to comparatively dry hilltops without streams. When disturbed it moves rapidly and emits a strong, unpleasant odor, and like its newly recognized relative it is presumed to feed primarily on earthworms. Several historical records, including a report from Laos, remain unverified for lack of voucher specimens.
Questions remain. Three museum specimens from Yunnan collected decades ago cannot yet be assigned with confidence, and a short, potentially contaminated cytochrome b sequence attributed to the species from Yunnan was excluded from the analysis. The 6.4 to 7.0 percent genetic divergence between Chinese and Vietnamese populations of true Hebius atemporalis, together with roughly 4 percent divergence between Guizhou and Guangdong populations within China, suggests that further cryptic diversity may still be lurking within the complex. The authors hypothesize that the species’ relatively fossorial habits may restrict dispersal and promote such population structuring, a premise that broader geographic sampling and multi-locus genomic datasets will be needed to test.
Perhaps the most evocative finding is biogeographic. The estimated divergence between Hebius malnatei and Hebius atemporalis, dated to roughly 6.8 million years ago, coincides closely with major uplift phases of the Yunnan-Guizhou Plateau. This supports a scenario of allopatric speciation driven by geological and climatic processes that carved the region into a mosaic of topographic barriers and montane refugia. The plateau is increasingly recognized as a hotspot for cryptic amphibian and reptile diversity, with numerous lineages of frogs and snakes showing similar patterns of local endemism. The discovery of Malnate’s keelback reinforces the region’s status as both a cradle of herpetofaunal speciation and a priority area for biodiversity research and conservation, and it serves as a reminder that even familiar, wide-ranging species can conceal evolutionary stories written in stone.
Subject of Research: Taxonomic revision of the Hebius atemporalis snake complex and description of a new keelback species from China
Article Title: Taxonomic reassessment of Hebius atemporalis (Bourret, 1934) ( Squamata , Natricidae ), with the description of a new species from China
Article References: Li, M.-L., Nguyen, T. V., Huang, J.-J., Idiiatullina, S. S., Le, S. X., Poyarkov, N. A., David, P., Han, B.-Y., Wu, W., Li, J.-T., & Ren, J.-L. (2026). Taxonomic reassessment of Hebius atemporalis (Bourret, 1934) (Squamata, Natricidae), with the description of a new species from China. Zoosystematics and Evolution, 102(1), 235-251. https://doi.org/10.3897/zse.102.176342
Image Credits: AI Generated
Keywords: Hebius malnatei, Hebius atemporalis, keelback snakes, Natricidae, Yunnan-Guizhou Plateau, integrative taxonomy, cytochrome b, cryptic species, herpetology, China, Vietnam, species delimitation
News Source: Drew Townsend. (October 18, 2026). Hidden Snake Species Unmasked on China’s Yunnan-Guizhou Plateau After Nearly a Century. Scienmag.
