Dipterocarps used India as a raft from Gondwana to Eurasia

Abstract

It has been hypothesized that most Asian tropical lineages have originated in Gondwana with the Indian subcontinent playing a crucial role in the dispersal of ancestral Gondwanan taxa. The disjunct distribution of dipterocarps and the fossil record in India support the Gondwana hypothesis. This is the first comprehensive study addressing the evolutionary and biogeographic relationships of dipterocarps in the Indian subcontinent to test the Gondwana hypothesis. A Bayesian phylogenetic tree of the Dipterocarpaceae family including the Indian counterparts corroborates the monophyly of subfamilies/tribes and shows new biogeographic affinities. Molecular dating reveals the Cretaceous origin of Dipterocarpaceae. Diversification of major lineages occurred during the Pliocene-Miocene epochs. The DEC analysis ascertains the Gondwanan origin and dispersal route from the Madagascar (Africa)-India-Sri Lanka-Seychelles block to Eurasia. The biogeographic analysis suggests early vicariance followed by an outof-India dispersal of Dipterocarpaceae. Three dispersal events from India to the remainder of Asia at 47.6 Ma, 42.53 Ma and 37.6 Ma are identified. There probably was a biotic interchange between India and mainland Asia via Sumatra following the collision of the Indian plate with Eurasia. Molecular dating and dispersal events coincide with the geological events. During the Miocene, uplift of the Himalayan-Tibetian plateau induced climatic variation, which seems to have resulted in the extinction of major Indian dipterocarp lineages and reverse dispersal into India. Hopea-Shorea, one of the earliest diverged lineages, originated in Southeast Asia. The establishment of Southeast Asian monsoon climate may have favoured allopatric speciation and diversification of Southeast Asian lineages also resulting in further dispersal into India.

First fossil woods and palm stems from the mid‐Paleocene of Myanmar and implications for biogeography and wood anatomy

“…Wheeler et al (2017) proposed that hot, tropical conditions at low latitudes accelerated adaptive xylem evolution to fit the high demands for hydraulic efficiency typical for the tropical lowlands. These observations support the role of the Indian subcontinent as a cradle for many taxa of angiosperms and a “raft” for biotic dispersal between Africa and Asia, supporting the “out‐of‐India” biogeographical hypothesis (Prasad et al, 2018; Bansal et al, 2022; Bolotov et al, 2022; Sanil et al, 2022). The lack of other early Paleocene fossil wood assemblages in low‐latitude South Asia hamper further testing of this hypothesis and raise questions about the temporal continuity of these early angiosperm‐dominated forests.…”