1. Institute of Geology; Chinese Academy of Geological Sciences; Beijing 100037 China
2. Key Laboratory of Stratigraphy and Paleontology; Ministry of Land and Resources of the People's Republic of China; Beijing 100037 China
3. State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany; Chinese Academy of Sciences; Beijing 100093 China
4. Laboratory of Palaeobotany, Komarov Botanical Institute; Russian Academy of Sciences; Saint Petersburg 197376 Russia