Guwahati: An Assamese researcher and his international team have uncovered a remarkable chapter in India’s natural history — a tiny skink found only in Kerala’s Western Ghats likely arrived there not from Northeast India, as long believed, but across the sea from Southeast Asia millions of years ago.
The study, published in Zoologica Scripta, was led by Pranoy Kishore Borah of the National Institute of Science Education and Research (NISER), Bhubaneswar. Working with collaborators from the University of Florida, La Sierra University in California, and the San Diego Natural History Museum, Borah pieced together a genetic puzzle that challenges long-held assumptions about the origins of Indian reptiles.
At the heart of the discovery is Sphenomorphus dussumieri, a small, forest-dwelling skink confined to the lush slopes of Kerala’s Western Ghats. While India is home to five species of Sphenomorphus, four occur in Northeast India — S. maculatus, S. indicus, S. courcyanus, and S. apalpebratus. For decades, herpetologists speculated that the Kerala species might be a distant cousin of these northeastern lizards, part of an ancient continuous distribution later fragmented by climatic changes.
But the new genetic analysis tells a different story. By sequencing DNA from skink specimens collected in Thattekad Bird Sanctuary and the Sabarimala foothills, the researchers discovered that S. dussumieri is not closely related to the species from Northeast India. Instead, it shares a more recent ancestry with skinks from the Sunda region of Southeast Asia.
“Our findings suggest that Sphenomorphus dussumieri reached Peninsular India through long-distance transoceanic dispersal around 21 million years ago,” Borah explained. “This likely occurred at a time when sea levels were lower and temporary land connections or island chains across the Andaman and Nicobar region made such journeys possible.”
The team’s ancestral range analysis indicates that the Northeast Indian skinks arrived via a separate dispersal event from Indo-China, while the Kerala species undertook an independent voyage across the ocean. The results point to at least two distinct colonization episodes, shaped by ancient sea-level fluctuations during the Oligocene–Miocene period.
For Borah, who hails from Assam, the discovery also highlights the unique role Northeast India plays in the region’s biogeography. “The Northeast has long been considered the westernmost edge of Southeast Asia’s biodiversity. While the Kerala skink came directly from Sunda, its cousins in the Northeast still carry the imprint of that broader Southeast Asian connection,” he noted.
The implications of the study go well beyond skinks. Similar biogeographic patterns have been observed in other reptiles and amphibians of the Indian subcontinent. Sri Lanka’s agamid lizards, certain microhylid frogs, and even flowering plants like wild gingers show evidence of ancient dispersal from Southeast Asia.
These findings challenge the long-held notion that India’s biodiversity is solely a legacy of its Gondwanan past and highlight the ocean’s role as both a barrier and a bridge for species movement.
The absence of S. dussumieri in Sri Lanka and the Nicobar Islands, Borah added, may be due to later sea-level rises that submerged possible corridors and caused local extinctions. “The ocean is often seen as an insurmountable barrier, but in evolutionary timeframes, it can act as a highway for species, whether through rafting on vegetation mats, swimming, or stepping-stone islands.”
The study also underscores how much remains to be discovered. Gaps in sampling across the Andaman and Nicobar Islands mean that related species may still await scientific description, potentially refining the timelines of dispersal events.
Funded by intramural support at NISER and a Science and Engineering Research Board (SERB) grant, the research relied on meticulous fieldwork and advanced genetic analysis. It reflects the growing strength of Indian-led collaborations in global biodiversity research.
As India grapples with biodiversity loss and habitat fragmentation, Borah believes such discoveries are more than academic. “Understanding how species came to India and adapted here helps us appreciate the uniqueness of our natural heritage,” he said. “These stories remind us that the Western Ghats and the forests of Northeast India are not isolated pockets, but part of a vast, interconnected evolutionary history.”
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