A Middle Eocene lowland humid subtropical "Shangri-La" ecosystem in central Tibet

The ancient topography of the Tibetan Plateau and its role in biotic evolution are still poorly understood, mostly due to a lack of fossil evidence. Our discovery of ∼47-Mya plant fossils from a present elevation of 4,850 m in central Tibet, diminishes, significantly, that lack of knowledge. The fossils represent a humid subtropical vegetation and some of the 70 different plant forms show affinity to Early-Middle Eocene floras in both North America and Europe. Using leaf architecture, we calculate that the forest grew at ∼1,500-m elevation within an east-west trending valley under a monsoonal climate. Our findings highlight the complexity of Tibet's ancient landscape and emphasize the importance of Tibet in the history of global biodiversity.