Claudia Johnson is an assistant professor of geological sciences at Indiana University, Bloomington. She received her Ph.D. from the University of Colorado, Boulder, in 1993 and was a post-doctoral investigator at Pennsylvania State University, where she integrated her database on reefs with computer models of past oceanic circulation. Specializing in reef evolution and extinction, Johnson has studied ancient and modern reef ecosystems in many parts of the world. She is currently investigating the persistence of reef ecosystems over 500 million years and the biological laws governing their latitudinal diversity. Address: Department of Geological Sciences, Indiana University, 1001 East 10th Street, Bloomington, IN 47405-1405. Internet: claudia@indiana.edu