Taxonomic diversity and floristic composition changes of East Asia during the early Paleogene

The early Paleogene floristic background and taxonomical inventory of palaeobotanical data of East Asia are studied for the first time using quantitative techniques. The record comprises 110 micro- and macrofloras from 73 localities of Eastern Siberia, Far East of Russia, China, and Japan. The analysis of the floral record reveals a taxonomical diversity of 1119 species of 578 genera from 132 families. Angiosperms represent the most diverse division accounting for over two-thirds of family diversity. The application of multivariate statistics provides insight into the floristic similarities of the single palaeofloras and the relation between taxonomic entities, and allows to trace the spatio-temporal distribution of six floristic groups characterised by taxonomic associations. The floristic composition in the study area did not undergo any significant changes throughout the early Paleocene, while the early Eocene saw a distinct increase mainly referable to a diversification of angiosperms. This diversification can possibly be related to the coeval warming trend. Our analysis of the Paleocene floras supports their continuity with Late Cretaceous floras, relative floristic homogeneity and the existence of only two floristic provinces. For the early Eocene we suggest at least three floristic provinces. Our results support a diffuse origin of the early Paleogene floras of East Asia and a lower to mid-latitudinal appearance of angiosperm taxa and a pole-ward migration thereafter, which generally supports the Boreotropical hypothesis. The early Paleogene floras of East Asia show minor spatial and temporal variations in taxonomic composition, with new taxa appearing in the fossil record at different times and having different ecologies.