The Cenozoic biogeographical evolution of woody angiosperms inferred from fossil distributions

Aim We test whether the modern regionalization of the angiosperm flora is the result of Cenozoic barriers to dispersal. Location Global. Methods We used a database of Cenozoic woody angiosperm fossils to build a matrix of family and genus occurrence at 11 continents/regions for five time periods of the Cenozoic, thus defining 55 floras. We used ordinations and cluster analyses to infer the relationships among these floras. We tested for the effects of time, land connections and dispersal barriers on the similarities between these woody angiosperm floras. Results For all time periods of the Cenozoic the world's woody angiosperm floras were grouped into three large clusters: a very compact Northern Hemisphere cluster (North America, Europe, temperate Asia and Palaeogene south China), a somewhat less compact Palaeotropical cluster (Africa, India, Southeast Asia and Neogene south China) and a rather diffuse Gondwanan cluster (Antarctica, Australia, New Zealand, temperate South America and the Neotropics). The primary clustering is evidently geographical, and reflects the barriers formed by the Tethys and the southern Atlantic-southern Indian oceans. There is evidence that the more recent Gondwanan floras are more divergent than the older floras, possibly due to long isolation by oceans and multiple extinction events, whereas the similarities among Northern Hemisphere floras increased during the Neogene. Main conclusions The modern regionalization is mainly the result of dispersal barriers that existed at diverse times in the Cenozoic, resulting in several woody angiosperm floras that evolved in parallel. Climatic change and dispersal also played important roles in shaping biogeographical patterns of Cenozoic woody angiosperms.