Occurrence of Dipterocarpus Fossil Wood and Leaf in the Western Siwalik Sector of Sarkaghat Area, Himachal Pradesh, India: Phytogeographical Implications

Abstract

Palaeobotanical investigations of plant megafossils, including fossil woods and leaf impressions, from the Middle Siwalik sediments of the Sarkaghat area in the Himalayan foothills of Himachal Pradesh, India, have revealed the presence of fossil wood and leaves belonging to the Southeast Asian genus Dipterocarpus C. F. Gaertn. (family Dipterocarpaceae). The fossil wood has been identified as Dipterocarpoxylon siwalicus Prakash, while the leaf impressions are assigned to Dipterocarpus miocenicus Prasad & Gautam.  A comparison with the present-day distribution of closely related extant species of Dipterocarpus shows that these taxa no longer occur in the Himalayan foothills of Himachal Pradesh. Instead, they are currently confined to the evergreen forests of Southeast Asia. This distribution pattern suggests that increasing arid conditions after the Miocene likely led to the local extinction of these taxa in the region. Based on fossil evidence and the biogeographical distribution of comparable living species, the phytogeographical implications of this finding are discussed. It is further inferred that Dipterocarpus migrated into the area from Southeast Asia during the early Miocene and subsequently disappeared due to the development of unfavourable climatic conditions.