Kenneth D. Rose is a professor at the Center for Functional Anatomy and Evolution at the Johns Hopkins University School of Medicine and a research associate at the Smithsonian National Museum of Natural History in Washington, D.C., and the Carnegie Museum of Natural History in Pittsburgh. J. David Archibald is Professor of Biology and Curator of Mammals in the Department of Biology at San Diego State University. In addition he is a Research Associate at the San Diego Museum of Natural History and the University of California Museum of Paleontology, Berkeley. For the past 10 years he has direc...