Ancient Fossil Leaves from Assam Reveal Lost Biodiversity Link with Western Ghats

In a remarkable discovery that sheds light on South Asia’s deep ecological past, a team of Indian scientists has identified fossilized leaves in Assam’s Makum Coalfield that belong to a plant genus now only found in the Western Ghats. These fossils, dating back approximately 24–23 million years to the late Oligocene epoch, offer the world’s oldest known record of the Nothopegia genus and reveal a long-lost biogeographical connection between India’s northeastern and southwestern ecological zones.

The research, led by scientists from the Birbal Sahni Institute of Palaeosciences (BSIP) in Lucknow — an autonomous institute under the Department of Science and Technology (DST), Government of India — utilized an interdisciplinary approach combining paleobotany, taxonomy, and climate modeling to unravel the story behind this ancient botanical migration.

Discovery in the Depths of Coal

The Makum Coalfield in Assam has long been known for its rich fossil repository. During a recent excavation, scientists stumbled upon fossilized leaf impressions that appeared strikingly similar to the foliage of modern Nothopegia, a genus of tropical trees that now thrive thousands of kilometers away in the rain-soaked Western Ghats, a UNESCO World Heritage Site and one of the world’s eight "hottest hotspots" of biodiversity.

Using morphological assessments, comparative studies with existing herbarium collections, and cluster analysis, the team confirmed the identity of the fossils. The revelation was staggering — Nothopegia, once native to Northeast India, has vanished from the region but continues to survive in the Western Ghats, making it a living relic of India’s ancient ecosystem.

Reconstructing a Lost Climate

To understand how this tropical plant once thrived in Assam, researchers employed the Climate Leaf Analysis Multivariate Program (CLAMP), a sophisticated tool that uses leaf morphology to reconstruct past climates. Their analysis revealed that the late Oligocene environment of Northeast India was warm, humid, and tropical, resembling the present-day conditions of the Western Ghats.

But this was before massive tectonic shifts forever altered the region’s climate. As the Himalayas began to rise, they changed atmospheric circulation patterns, disrupted rainfall, and caused the northeast to cool. Over time, this dramatic environmental shift made the area inhospitable for tropical flora like Nothopegia, which was forced to retreat. The Western Ghats, by contrast, offered stable climatic refuge — and the species endured.

Climate Change, Then and Now

The fossil record of Nothopegia offers more than a tale of ecological nostalgia. It provides critical insights into how species migrate, adapt, or go extinct in response to climate fluctuations — a process that has shaped biodiversity for millions of years.

“This is not just about ancient plants disappearing,” said co-author Dr. Harshita Bhatia. “It’s about understanding how life on Earth has historically responded to environmental pressures and how this can inform our conservation efforts today.”

The parallels between ancient and modern climate shifts are alarming. While historical changes took millennia, today’s climate is changing at an unprecedented rate, primarily due to human activity. The Nothopegia saga becomes a cautionary tale — demonstrating the risks species face when they cannot migrate or adapt quickly enough.

The Importance of Biodiversity Refuges

The study underscores the importance of protecting biodiversity refuges such as the Western Ghats, which harbor not just biodiversity but entire evolutionary histories. These ecological time capsules are critical in sustaining genetic diversity and offer crucial insights into the resilience of life.

The research has been published in the journal Review of Palaeobotany and Palynology, and marks a significant step forward in South Asia’s paleobiogeographical research.

By combining fossil studies with modern climate modeling, the team has opened a new window into how Earth’s biodiversity corridors were formed — and how fragile they can be. Protecting these corridors today could be the key to ensuring biodiversity survives tomorrow.