Christine M. Janis is Professor of Biology in the Department of Ecology and Evolutionary Biology at Brown University, Rhode Island. She is on the editorial board of Journal of Mammalian Evolution and Acta Paleontologica Polonica, and Associate Editor for the journal Evolution. Professor Janis was also editor-in-chief for Evolution of Tertiary Mammals of North America, Volume 1: Terrestrial Carnivores, Ungulates, and Ungulate like Mammals (Cambridge, 1998). Gregg G. Gunnell is Associate Research Scientist in the Museum of Paleontology at the University of Michigan. He is Associate Editor for the journal Palaois, Past Associate Editor for Journal of Human Evolution, and a Member of the Society for Vertebrate Paleontology, the Paleontological Society, and the American Society of Mammalogists. Mark D. Uhen is Head of Research and Collections and Curator of Paleontology and Zoology at the Cranbrook Institute of Science. He is a Research Associate in the Department of Paleobiology at the US National Museum of Natural History, Chair of the Society of Vertebrate Paleontology Patterson Award Committee, and a member of the Advisory Board and the Vertebrate Working Group for the Paleobiology Database.