1. Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, MRC 121, PO Box 37012, Washington, DC 20013-7012, U.S.A., ,
2. Department of Biology, University of Central Oklahoma, Edmond, Oklahoma, 73034, U.S.A.,
3. Dinosaur Institute, Natural History Museum of Los Angeles County, Los Angeles, California, 90007, U.S.A.