Guwahati: Fossilised plant leaves discovered in Manipur suggest that the region supported lush tropical vegetation around 30 million years ago, offering new insights into the ancient climate and vegetation history of Northeast India.
The findings come from a new study published in the Journal of the Botanical Society of Bengal, which documents several plant megafossils from the Laisong Formation dating to the late Eocene–early Oligocene period.
The research, conducted by Harshita Bhatia and Gaurav Srivastava of the Birbal Sahni Institute of Palaeosciences in Lucknow, identified multiple dicot leaf fossils and fragments of palm leaves from sites in the Thoubal and Senapati districts of Manipur.
According to the researchers, the fossil assemblage indicates that the region experienced a warm, humid and frost-free tropical climate during that period.
“The presence of palms suggests a frost-free climate with high moisture availability, and the combination of dicot leaf physiognomic features suggests that the Laisong flora grew under warm and humid tropical conditions,” the authors wrote.
Scientists often consider palm fossils as strong indicators of tropical climates because palms generally grow in warm environments with abundant rainfall and no frost.
Climate reconstruction based on fossil leaf characteristics suggests the region had an average annual temperature of about 25.3°C and annual rainfall of around 244 cm, indicating conditions similar to modern humid tropical monsoon climates.
The study also points to a strong seasonal rainfall pattern, with heavy summer precipitation and relatively drier winters.
Importantly, the research suggests that Northeast India may have remained a climatic refuge for tropical vegetation during a major global cooling phase known as the Eocene–Oligocene transition, when Antarctic glaciation intensified.
“The continued presence of palm-rich tropical forests even during the EOT suggests that Northeast India may have served as a humid refugium buffered from extreme climatic fluctuations,” the researchers noted.
The fossils were recovered from sedimentary rocks of the Laisong Formation, which were deposited in shallow coastal and deltaic environments, indicating that parts of Manipur were once influenced by near-marine conditions.
The researchers say the discovery helps fill an important gap in the poorly documented fossil plant record of Northeast India, improving scientific understanding of the region’s ancient vegetation and climate.
“These new fossils contribute to improving the understanding of Paleogene vegetation and climatic conditions in Manipur during the late Eocene–early Oligocene,” the study states.
Explaining what the region may have looked like millions of years ago, lead author Harshita Bhatia said a traveller visiting Manipur around 30 million years ago would likely have encountered dense tropical forests dominated by broad-leaved trees and palms.
“The presence of palm fossils itself indicates warm, humid and frost-free conditions, suggesting evergreen vegetation,” Bhatia said.
She added that the sedimentary deposits indicate environments such as deltaic plains, river systems and coastal wetlands, meaning the landscape was probably a mosaic of forests, swamps and coastal habitats.
However, she noted that the fossil record of animals from the region remains limited, making it difficult to reconstruct the wildlife that once inhabited these ecosystems.
Bhatia also said the discovery is significant because Manipur remains one of the least explored regions in India for plant fossil studies.
“While fossil floras have been reported from Assam, Meghalaya and Nagaland, the fossil record from Manipur is still very sparse. Our findings help fill an important gap in reconstructing the region’s ancient vegetation and climate,” she said.
According to the researchers, the fossils show that Manipur supported warm and humid tropical forests even during a period of major global climatic reorganisation about 30 million years ago.
When combined with similar fossil records from Nagaland, the findings indicate that much of Northeast India maintained tropical vegetation and strong seasonal rainfall patterns during that time.
Bhatia said this evidence suggests the region may have functioned as a tropical climatic refugium during global cooling phases.
“In many parts of the world, tropical ecosystems declined during the Eocene–Oligocene cooling. However, our fossil evidence suggests that Northeast India remained warm and humid enough to sustain tropical forests, indicating remarkable climatic stability,” she explained.
She added that earlier fossil evidence from Manipur, including a fossil thorny bamboo from Ice Age deposits around 37,000 years old, also indicates that tropical vegetation persisted in the region even during later cooling events.
The fossils may also offer clues about the early development of the Indian monsoon system.
While the Manipur fossils alone cannot fully reconstruct the origin of the monsoon, Bhatia noted that fossil leaf assemblages from nearby Nagaland suggest strong seasonal rainfall patterns typical of monsoonal climates around 30 million years ago.
“Taken together, these findings suggest that monsoon-like climatic conditions were already influencing Northeast India around 30 million years ago, although more fossil discoveries will be needed to understand these systems in greater detail,” she said.
Scientists believe such long-term persistence of tropical forests may also help explain the extraordinary biodiversity seen in the region today.
“Northeast India is one of the world’s major biodiversity hotspots, and fossil evidence suggests that tropical forests have existed here for tens of millions of years,” Bhatia said. “Such long-term environmental stability can allow ecosystems to persist and diversify over very long periods.”
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