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It is shown that beta diversity among level, soft-bottom communities also increased significantly during the early Paleozoic.

The increase is insufficient, however, to account for the 300 percent rise observed in global generic diversity. As first shown by Bambach (1977), alpha diversity increased by 50 to 70 percent in offshore marine environments during the Ordovician and then remained essentially constant of the remainder of the Paleozoic. A data set consisting of 505 faunal lists distributed among 40 stratigraphic intervals and six environmental zones was used to investigate how variation of alpha and beta diversity influenced global diversity through the Paleozoic, and especially during the Ordovician radiations.

Global taxonomic richness is affected by variation in three components: within-community, or alpha, diversity, between-community, or beta, diversity and between-region, or gamma, diversity.