Plant fossils from Arung Khola and Binai Khola formations of Churia Group (Siwalik), west central Nepal and their palaeoecological and phytogeographical significance

Abstract

Systematic study of plant megafossils comprising dicotyledonous leaves and seeds collected from the Arung Khola and Binai Khola formations of the Churia Group, exposed in Tinau Khola and Mahendra Highway between Barghat and Dumkibas, Nepal, has revealed 15 taxa out of which 14 are new belonging to 14 genera of 12 families. They are named as Orophea siwalika sp. nov., Miliusa brochidodroma sp. nov. (Annonaceae); Gynocardia butwalensis sp. nov. (Flacourtiaceae); Shorea miocenica sp. nov., S. nepalensis sp. nov., Hopea siwalika Antal & Awasthi (Dipterocarpaceae); Grewia mallotophylla sp. nov. (Tiliaceae); Chisocheton ellipticus sp. nov., Ventilago ovatus sp. nov. (Rubiaceae), Swintonia butwalensis sp. nov. (Anacardiaceae); Mitragyna tertiara sp. nov., Mussaendopsis suborbiculatus sp. nov. (Rubiaceae); Alangium nepalensis sp. nov. (Alangiaceae); Homonoia lanceolata sp. nov. (Euphorbiaceae) and Ficus miocenicus sp. nov. (Moraceae). The modern counterparts of these fossils are mostly distributed in the tropical evergreen to semi-evergreen forests of Indo-Malayan region which indicate the existence of similar types of forests in the frontal Himalayan foot-hill zone during the Middle Miocene-Pliocene. The absence of tropical evergreen dipterocarps and their associates in the present-day flora of this region reflects changes in the annual mean temperature and rainfall caused by further uplift of the Himalayas and the northward movement of the Indian Plate.