1. Centre for Vertebrate Evolutionary Biology Yunnan University Kunming 650500 China
2. Key Laboratory of Vertebrate Evolution and Human Origins Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences Beijing 100044 China
3. Department of Biological Sciences George Washington University Washington DC 20052 USA
4. Royal Tyrrell Museum of Palaeontology Box 7500, Drumheller Alberta T0J 0Y0 Canada
5. Department of Biological Sciences University of Alberta 116 Street and 85 Avenue Edmonton AB T6G 2R3 Canada