1. Field Museum of Natural History Chicago Illinois 60605 U.S.A.
2. Key Laboratory of Vertebrate Evolution and Human Origins Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences Beijing 100044 China
3. CAS Center for Excellence in Life and Paleoenvironment Beijing 100044 China
4. College of Earth and Planetary Sciences, University of Chinese Academy of Sciences Beijing 100049 China
5. Department of Earth and Environmental Sciences Dixie State University St. George Utah 84770 U.S.A.
6. Section of Vertebrate Paleontology, Carnegie Museum of Natural History Pittsburgh Pennsylvania 15213 U.S.A.
7. Department of Earth Sciences University of Oxford Oxford OX1 3AN UK