A mid-Cretaceous island as a cradle of Southeast Asian plant biodiversity

The renowned tropical flora of Southeast Asia is often regarded as being of relatively recent (Cenozoic) origin. Here, based on specimens embedded in mid-Cretaceous amber obtained from Kachin, Myanmar, we report on a large assemblage of exceptionally well-preserved plant fossils encompassing a rich diversity of angiosperms, together with many other seed plants and cryptogams. The morphospecies richness and clade diversity of this flora are among the highest recorded for any single Early to mid-Cretaceous plant megafossil assemblage. This ancient flora reached Southeast Asia rafted on the West Burma Block, an arc-shaped microplate that separated from the northwestern corner of the Australian Plate during the Jurassic and drifted north, finally colliding with Sundaland by the Eocene. The Burma Terrane remained low lying and at low latitudes in the intervening 100-50-million-year period, providing a sanctuary for clade preservation, a cradle for modern clade diversification and a conduit for transferring flourishing Gondwanan angiosperm lineages to Asia. These findings provide insight into the cradle of what ultimately became Southeast Asian angiosperm-dominated tropical forests, whose origins date back over 100 million years.