We greatly appreciate this opportunity to contribute to the volume for a field man and a friend, Will Downs, who had such deep love of working in Asia and of Chinese culture. We thank L.J. Flynn and A. Winkler for instructive comments on the manuscript. This project has been supported by NSF grant (EAR-0120727) to Meng and collaborators and by the Institute of Vertebrate Paleontology and Paleoanthropology, Beijing, Chinese Academy of Sciences. We thank M.A. Erbajeva for providing the translation of a Russian reference.