This research was funded by grants from the National Basic Research Program of China (973 Program) (No. 2012CB821900); The National Natural Science Foundation of China (No. 31372242, 41272006, 31230065); Fok Ying-Tong Education Foundation for Young Teachers in the Higher Education Institutions of China (No. 131021); Project of Outstanding Young-aged Talents of Beijing Municipal Commission of Education (No.CIT & TCD201304163); the Project of Great Wall Scholar and KEY project of Beijing Municipal Commission of Education (grants KZ201310028033) and the State Key Laboratory of Palaeobiology and Stratigraphy (Nanjing Institute of Geology and Palaeontology, CAS) (No.123114).