1. State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, P.R. China;
2. Department of Earth Sciences, Western University, London, Ontario N6A 5B7, Canada
3. Department of Earth Sciences, Brandon University, Brandon, Manitoba R7A 6A9, Canada
4. College of Earth and Space Sciences, Peking University, Beijing 100871, P.R. China