FIG. 23.21 Mass extinctions. Though they eliminate much of the life found on Earth at the time, mass extinctions allow new groups to proliferate and diversify. Source: Sepkoski’s Online Genus Database. http://strata.geology.wisc.edu/jack/. Data from J. J. Sepkoski, Jr., 2002, “A Compendium of Fossil Marine Animal Genera,” David Jablonski and Michael Foote (eds.), Bulletin of American Paleontology 363:1–