A narrow isthmus that repeatedly connected and separated Sri Lanka from India as sea levels changed. Genetic differences between Indian and Sri Lankan elephants reveal how these connections shaped wildlife migration.
This Image was created by User:PlaneMad. If you are using the image under the creative commons share alike license please credit the photo CC-by-sa PlaneMad/Wikimedia and include a link to this page. No explicit permission is needed from me, but id appreciate an email if my work has been of help to you. If you dont want to release your work under a creative commons license, please mail me at arun.planemad@gmail.com or catch me at my Website to negotiate a custom license as per your needs., CC BY-SA 2.5, via Wikimedia Commons
An ice age land bridge
Elephant Pass is the narrow gateway to Sri Lanka's Jaffna Peninsula, but is part of a larger and more ephemeral structure: a land bridge that once connected Sri Lanka to the Indian subcontinent. This connection, often called Adam's Bridge, is a 48-kilometer chain of limestone shoals running from Mannar Island in Sri Lanka to Pamban Island in India. For much of the Pleistocene, this was not a string of islands but a continuous land corridor.
During the Last Glacial Maximum, around 20,000 to 26,000 years ago, massive ice sheets locked up vast amounts of water. Global sea levels dropped by as much as 120 to 130 meters, exposing the shallow floor of the Palk Strait and creating a wide bridge between the two landmasses. This land connection appeared and disappeared multiple times in cycles of glacial and interglacial periods. The Palk Strait, with a maximum depth of only 35 meters, became a freshwater basin fed by rivers when sea levels were at their lowest. The final land link was likely severed by rising seas around 7,000 years ago.
The DNA record
The repeated connection and separation filtered for animal migration. One example is the Asian elephant. Genetic analysis shows a split between the mainland Indian elephant (Elephas maximus indicus) and the Sri Lankan elephant (Elephas maximus maximus). Genome analysis estimates this divergence occurred approximately 48,000 years ago, a time corresponding to a period when rising sea levels would have submerged the land bridge and isolated the Sri Lankan population.
While elephants successfully made the crossing and became a distinct population, other large Indian fauna did not. The land bridge was an arid habitat, which would have been unsuitable for species adapted to dense forests. This environmental filtering explains why animals like tigers and other megafauna, present in India, but never established long-term populations in Sri Lanka. The island's fossil record shows evidence of extinct hippos and rhinoceroses that did cross during earlier connections, but the fauna today is a distinct subset of what is found on the mainland.
The genetic story of Sri Lanka's elephants is complex; some studies show they cluster closely with elephants from Myanmar, possibly due to ancient trade routes. Within Sri Lanka itself, there are at least three genetically distinct elephant clusters, shaped by internal barriers and social organization.
💡Fun Facts
Temple records from Rameswaram suggest the land bridge was walkable until a major cyclone destroyed it in 1480.
During the Last Glacial Maximum, the exposed Palk Strait likely functioned as a large freshwater lake, fed by rivers from both India and Sri Lanka.
The name 'Elephant Pass' dates to the Dutch colonial period, when elephants were herded across the shallow lagoon at this point for export.
The full land connection, Adam's Bridge, is a 48 km (30 mile) long chain of limestone shoals.
