Warren D. Allmon is director of the Paleontological Research Institution in Ithaca, New York, and adjunct associate professor in the Department of Earth and Atmospheric Sciences at Cornell University. He is coeditor of Causes of Evolution: A Paleontological Perspective.David J. Bottjer is professor of earth sciences at the University of Southern California and the editor (with Richard K. Bambach) of two Columbia University Press book series: Critical Moments in Paleobiology and Earth History and Perspectives in Paleobiology and Earth History. He has also been editor of the journal Palaios and currently is one of the editors of the journal Palaeogeography, Palaeoclimatology, Palaeoecology.