1. State Key Laboratory of Continental Dynamics Shaanxi Key Laboratory of Early Life & Environments Department of Geology Northwest University Xi'an 710069 China
2. Department of Palaeobiology Swedish Museum of Natural History Box 50007 SE‐104 05 Stockholm Sweden
3. State Key Laboratory of Palaeobiology and Stratigraphy Nanjing Institute of Geology & Palaeontology Chinese Academy of Sciences Nanjing 210008 China