New Giant Groundsnake Species Hidden in Peru’s Cloud Forests Finally Gets a Name

Deep in the humid montane forests of northern Peru, a large, secretive snake has been hiding in plain sight for more than a decade. Researchers have now formally described it as a new species, Atractus paulus, after a painstaking re-examination of museum specimens revealed that the Peruvian population long labeled as the giant groundsnake Atractus gigas is in fact a distinct animal. The discovery, published in the journal Evolutionary Systematics, is a striking reminder that even sizable species can slip through the taxonomic net when the right characters are overlooked.

The genus Atractus, established in 1828 by the German naturalist Wagler, is one of the most diverse groups of dipsadid snakes in the Neotropics, with roughly 150 species known to date. These cryptozoic snakes spend much of their lives underground or beneath leaf litter, which makes encounters with humans rare and complicates field studies. Many are relatively small, but a handful of giants exceed 600 millimeters in snout-vent length, and it is among these large Andean species that confusion has persisted. Descriptions of giant Atractus in the Andes have historically been based on small samples, leaving ample room for misidentification.

The story of the new species began when Atractus gigas was described in 2006 from a single specimen collected at Bosque Protector Río Guajalito, between Quito and Santo Domingo in Ecuador. Four years later, researchers reported the first live specimen in primary cloud forest at Bosque Protector Santa Lucía, and additional material from Peru extended the supposed range of the species across the Andes. Yet even then, the Peruvian specimens stood out: they had fewer subcaudal scales than their Ecuadorian counterparts, more supralabial and infralabial scales, and a different arrangement of scales contacting the chinshields. Despite these red flags, the Peruvian snakes were treated as the first record of a single Atractus species on both sides of the Andes.

Suspicion grew over the following years. Recent work by Arteaga and colleagues raised concerns about the status of Atractus gigas along the eastern versant of the Andes, noting that scutellation and ontogenetic variation between Ecuadorian and Peruvian specimens are easily diagnosable, and suggesting that the Peruvian snakes might belong to Atractus atlas or represent something entirely new. Prompted by these questions, the authors of the new study undertook an exhaustive revision of external morphological characters, examining 145 specimens of Atractus from Brazil, Ecuador, and Peru held in ten museum collections, with additional photographs obtained from institutions in Germany and the United States.

The decisive evidence came from a character system that has long been underreported in the genus: apical pits, tiny depressions on the surface of dorsal scales. The Peruvian snakes possess two apical pits on their dorsal scales near the cloaca, a feature not shared by any of the other giant Andean species. Combined with differences in head scalation, including the number of infralabials contacting the chinshields, and the count of subcaudal scales, the presence of apical pits firmly separates the Peruvian population from Atractus gigas and from all other congeners. The new species is known from just two specimens: an adult female holotype collected at Alto Ihuamaca in Cajamarca department at 1,641 meters, and a juvenile paratype from El Chaupe at 2,161 meters, both gathered in August 2008.

Atractus paulus is unmistakably a giant among groundsnakes. The adult female holotype measures 830 millimeters in snout-vent length, with a moderately short tail accounting for just over nine percent of that figure. Its dorsal scales are arranged in seventeen smooth rows, and its coloration in preservative is a yellow ochre above, with a mostly black ventral surface in juveniles that becomes uniform brown in adults. Among the roughly 150 species in the genus, only eight others exceed 600 millimeters in body size, and nearly all of them bear dorsal bands that contrast with the uniform dorsum of the new species. The name paulus, Latin for small, is a playful nod to the tiny type series, but it also honors Dr. Paulo Gustavo Homem Passos, a herpetologist who has described more than 34 Atractus species, roughly one-fifth of the genus’s astonishing diversity.

The detailed description of the holotype reveals a snake of considerable anatomical interest. The adult female carried twelve eggs in her oviduct, each measuring between 30 and 36 millimeters in length, evidence of substantial reproductive investment. The maxillary bone bears eight robust, posteriorly curved teeth with angular cross-sections, examined in situ under a stereomicroscope through a narrow incision. The head scalation follows a precise formula: eight supralabials with the fourth and fifth contacting the eye on the left side, eight infralabials with the first four touching the chinshields, and a temporal formula of one plus two. Such characters, measured to a tenth of a millimeter with digital calipers, form the backbone of the species’ diagnosis in the absence of molecular data.

The revision also forced a broader reckoning with the genus’s history. In re-examining specimens of Atractus duboisi and Atractus orcesi, the authors found that apical pits are present in both species, contradicting earlier diagnoses that had omitted or denied this feature. Building on previous molecular phylogenetic results and the shared presence of apical pits, they formally named the Atractus duboisi group, comprising Atractus discovery, Atractus duboisi, Atractus orcesi, and the newly described Atractus paulus. Two other rare species, Atractus ecuadorensis and Atractus resplendens, were deliberately left out of the group because the relevant voucher specimens could not be verified, illustrating the authors’ insistence that hypotheses of species relationships be grounded in multiple, checkable lines of evidence.

Beyond the taxonomy, the discovery carries a conservation warning. The montane forest below 2,000 meters in San Ignacio province has almost entirely disappeared due to agricultural expansion, and both known localities of Atractus paulus sit in landscapes dominated by coffee plantations and cattle pastures, with only scattered patches of remaining forest and secondary vegetation. The protected forests of the National Sanctuary Tabaconas Namballe lie only five to nine kilometers away, but they preserve habitat above 2,000 meters, potentially beyond the snake’s altitudinal range. Because so little is known about the species’ distribution, the authors could not apply IUCN criteria to assign a conservation category, yet they urge that its status be rapidly reassessed given the level of habitat destruction in the region.

The description of Atractus paulus ultimately tells two stories at once. It adds a charismatic new giant to one of South America’s most species-rich snake genera, and it delivers a pointed critique of modern taxonomy’s growing neglect of traditional morphological detail. The authors argue that the rush to publish molecularly oriented, integrative taxonomy has led to increasingly basic and inadequate diagnostic comparisons, allowing informative character systems such as scale ornamentation and hemipenial morphology to fall by the wayside. Until systematic collecting resumes in the Andes, they note, the discovery of new reptile species will remain a product of serendipity, and understanding snake relationships in this vicariant landscape will stay in its infancy. For now, a large and long-misidentified snake of Peru’s cloud forests finally has a name of its own.

Subject of Research: Taxonomic description of a new species of groundsnake from the Peruvian Andes based on morphological characters

Article Title: A new species of groundsnake genus Atractus Wagler, 1828 ( Serpentes , Dipsadidae ) from the Peruvian Andes revealed by unequivocal morphological characters

Article References: Melo-Sampaio, P. R., & Venegas, P. J. (2023). A new species of groundsnake genus Atractus Wagler, 1828 (Serpentes, Dipsadidae) from the Peruvian Andes revealed by unequivocal morphological characters. Evolutionary Systematics, 7(2), 257-266. https://doi.org/10.3897/evolsyst.7.102578

Image Credits: AI Generated

DOI: 10.3897/evolsyst.7.102578

Keywords: Atractus, groundsnake, Peru, Andes, herpetology, taxonomy, new species, apical pits, Dipsadidae, cloud forest, morphology, conservation