Figure 23.3 Mass extinctions. Over the past 500 million years, there have been five mass extinctions. During these periods, the world experienced a significant decline in the number of families, which also means there were declines in the number of genera and species. Continued speciation during subsequent years has helped to offset these extinctions.

Data from J. J. Sepkoski, Jr., Ten years in the library: New data confirm paleontological data, Paleobiology 19 (1993): 43–51.