Vegetation changes across the Eocene-Oligocene transition: Global signals vs. regional development

The Eocene-Oligocene transition (EOT) marked a rapid global cooling event, often considered as the beginning of the modern icehouse world. Influenced by various factors, including tectonic activity and paleogeographic settings, the terrestrial records indicate a diverse response of fauna and vegetation to this global event. We examined nine macrofossil assemblages from seven fossil localities on the southeastern margin of the Tibetan Plateau and from the mid-latitudinal Europe ranging from the latest Bartonian and Priabonian (37.71–33.9 Ma) to the Rupelian (33.9–27.82 Ma). Our aims were to trace and compare the vegetation history of both regions in the late Eocene and early Oligocene. The results show that both regions experienced changes in vegetation composition in response to climate change, characterized by a decrease in the percentages of broad-leaved evergreen elements and distinctive changes in general vegetation types. A general change in the overall vegetation type from subtropical broad-leaved evergreen forests in the late Eocene to temperate broad-leaved mixed deciduous evergreen forests, or mixed mesophytic forests, in the early Oligocene is recognized in both regions. The results indicate a clear change in leaf architecture, leaf margin states, and secondary venation types in the mid-latitudinal Europe, while the results from the south-eastern margin of the Tibetan Plateau show a distinct reduction in leaf size. Our data suggest that both global and regional factors played key roles in shaping the vegetation in the two regions.