A team of ecological scientists from the Indian Institute of Science, Chennai Snake Park, and Bombay Natural History Society have discovered a new species of vine snake whose origin is believed to date back 26 million years. The vine snake has been named as Proahaetulla antiqua, after the Latin word ‘antiqua’ meaning ancient.
In 2011, while working on the classification and biogeography of snakes in the Western Ghats, the scientists came across a ‘visually unusual’ vine snake in the Agasthyamalai Hills.
The snake was found sleeping, coiled on a tree branch inside a forest patch on a hill on the way to Agasthyar peak. “Just by looking at it, I knew that it was a new species,” said Dr Ashok Kumar Mallik, one of the main researchers involved in the study. “People working in the field for a long time can immediately spot differences. This snake was superficially similar to another vine snake Ahaetulla dispar, but I could see that the scales were different,” he added.
Genetic analysis revealed that it was not only a new species, but it belonged to an entirely new genus. “Describing a new genus is subjective and varies across different taxa,” Dr Mallik said. “But generally for a new genus to be described, it should differ from other genera in a number of characteristics,” he explained.
To describe and prove a new genus is a challenging work. It needs careful analysis and thorough validation, which is a time-consuming process. Which is why although the specimen was found in 2011, the final confirmation and study was published in PLOS One, a peer-reviewed, open access scientific journal, in July 2019, after obtaining enough scientific evidence.
Vine snakes belong to the subfamily Ahaetuliinae, a group of tree climbing snakes, which currently consists of four genera — Ahaetulla, Dryophiops, Dendrelaphis and Chrysopelea. Most vine snakes in India and South Asia belong to the genus Ahaetulla. Ahaetulla and Dryophiops (widely found in Southeast Asia) are sharp-nosed snakes with horizontal pupils.
Proahaetulla antiqua differed from the Ahaetulla and Dryophiops genera in three genes. Given the strong genetic difference in these three genes, and several morphological differences, the scientists had enough proof to describe the new specimen as a new genus.
Like Ahaetulla, Proahaetulla antiqua had a sharp nose. But it had a set of 20 teeth as opposed to 12–16 in Ahaetulla. It had a greenish-yellow tongue with black speckles vs the reddish, purplish or brownish tongue in Ahaetulla. And the dorsal scales were mildly serrated compared to Ahaetulla’s smooth ones.
This new genus, Proahaetulla was classified as part of Ahaetuliinae family, sharing ancestry with genus Ahaetulla. The scientists also tested the evolutionary history of Proahaetulla antiqua, using a method called divergent dating, and found that it had diverged from other known vine snake species around 26 million years ago.
Finding an ancient species is rather unusual. Some ancient species of frogs and lizards have been discovered in the Western Ghats, noted Dr Mallik. “Many of these specimens were actually collected long before and kept in museums, but were never described or classified. We searched in all museums, but this species was never collected or found before” he concluded.
This makes it a rather unique discovery, and it also underscores the rich diversity and evolutionary history of reptiles in India and of the Western Ghats.