1. State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, and Center for Excellence in Life and Palaeoenvironment, Chinese Academy of Sciences , Nanjing 210008 , China
2. College of Earth and Planetary Sciences, University of Chinese Academy of Sciences , Beijing 100049 , China
3. Department of Geology , Hanover College, Hanover , IN 47243 , USA
4. Department of Invertebrate Paleontology , Cincinnati Museum Center, Cincinnati , OH 45203 , USA