Blaine W. Schubert is research associate in Geology, Department of Environmental Dynamics at the University of Arkansas.Jim I. Mead, is Professor of Geology and Paleonotology and Director of the Quaternary Sciences Program at Northern Arizona University.Russell Wm. Graham is Chief Curator and Head of the Collections and Research Branch, Department of Earth and Space Sciences, Denver Museum of Nature & Science. He has edited three books and published more than 50 professional papers on evolution, biogeography, and extinction of Quaternary mammals.