1. School of Earth Sciences; The Ohio State University; Columbus OH 43210 USA
2. State Key Laboratory of Palaeobiology and Stratigraphy; Nanjing Institute of Geology and Palaeontology; Chinese Academy of Sciences; 39 East Beijing Road Nanjing 210008 China
3. Department of Geology; Lund University; Sölvegatan 12 SE-223 62 Lund Sweden