Phylogenetic structure and palaeobiogeography of the Indian paleogene vegetation a study based on pollen fossil record from the lignites of Western India

Abstract

The plant fossils in the Tertiary lignites of north-western India suggest the presence of rainforests during early Paleogene. The present study reports the oldest fossils of Ebenaceae, Dipterocarpaceae, Linaceae and subfamily Crotonoideae, that represent a significant portion of tropical rainforests. The study reconstructs the palaeobiogeography of Crotonoideae based on the distribution of its fossil and extant species. Pollen morphological characters of the fossils and extant species of the remaining three families were combined with their molecular data under a phylogenetic framework to reconstruct their palaeobiogeographic histories. The study that Crotonoideae, Dipterocarpaeae originated in the seasonally wet areas of suggests Ebenaceae and newlineAfrica during mid-Cretaceous and dispersed to the Indian Plate via Kohistan-Ladakh Island Arc in Maastrichtian-Paleocene. During early Paleogene, the low temperature gradient across the equatorial and polar latitudes facilitated the spread of the three angiosperms to mid-high latitudes newlinevia boreotropical routes. However, majority of these lineages retreated to low latitudes as a result of global aridity during late Eocene-Oligocene. The movement of the Indian Plate in the perhumid climatic setting of equatorial region during the late Paleocene-early Eocene further provided an ecological opportunity to plant lineages to undergo allopatric speciation. Post India-Asia collision, the plant lineages migrated to Southeast Asia, where they diversified giving rise to the rich tropical lowland rainforests, supporting quotOut-of-Indiaquot hypothesis. The study further argues that the palaeobiogeographic hypotheses proposed for the three angiosperms are equally valid for the plant family Linaceae which has extant members in both tropical and temperate regions. newline newline