A major goal of paleobiological research since the early 1960s has been the reconstruction in quantitative terms of the history of biological diversity. Spearheaded by Valentine (1969), Raup (1972, 1976a, b), and Sepkoski (1979, 1981, 1984, 1990, 1993), this effort has yielded estimates of global diversity through time, as well as calculations of global rates and magnitudes of extinction and diversification. A consensus emerging in the early 1980s (Sepkoski et al. 1981) indicated that global marine invertebrate diversity rose through the Cambrian and Ordovician periods to a plateau, which with brief extinction-related interruptions was maintained from the mid-Paleozoic to the mid-Mesozoic. Beginning in the Cretaceous, diversity rose again, reaching a peak in the late Neogene. The five mass extinctions of the Phanerozoic, and more or less distinct episodes of diversification, were identified and distinguished from many lesser events (Raup and Sepkoski 1982). Comparable studies, with varying results, were conducted on land vertebrates (Benton 1985, 1989), land plants (Knoll et al. 1979; Niklas et al. 1980, 1983; Tiffney 1981; Knoll 1984), early protistans (Knoll 1994), insects (Labandeira and Sepkoski 1993), and life as a whole (Van Valen 1984, 1985; Van Valen and Maiorana 1985; Signor 1990; Valentine et al. 1991; Benton 1995; Courtillot and Gaudemer 1996; Miller and Foote 1996).