ACKNOWLEDGMENTS
We are grateful to R. F. Diffendal Jr. for his linguistic help. We thank especially two anonymous reviewers for greatly improving the manuscript. National Natural Science Foundation of China (grants 41472013 and 41472026), the Chinese Academy of Sciences Strategic Priority Research Program Grant B ‘Macroevolutionary Processes and Paleoenvironments of Major Historical Biota’ (no. XDPB05) supported this research. This study was aided by permission to observe some recent snake specimens under the care of L. Jun, Y. Hongyu, S. Jingsong, and L. Dongsheng, all of the Institute of Vertebrate Paleontology and Paleoanthropology. We thank the reviewers and the editors for their comments on an earlier version of the manuscript.