J. John Sepkoski Jr., (July 26, 1948 - May 1, 1999), was a University of Chicago paleontologist. Sepkoski studied the fossil record and the diversity of life on Earth. Sepkoski and David Raup contributed to the knowledge of extinction events. They suggested that the extinction of dinosaurs 65 mya was part of a cycle of mass extinctions that may have occurred every 26 million years.
Life and work 
Sepkoski was born in Presque Isle, Maine. In 1970, Sepkoski received a B.S. degree, magna cum laude, from the University of Notre Dame. Under Stephen Jay Gould he earned a Ph.D. in geological sciences from Harvard University in 1977. His Ph.D. was on the field geology and paleontology of the Black Hills of South Dakota. From 1974 to 1978, Sepkoski taught at the University of Rochester. In 1978 he joined the University of Chicago and became a professor in 1986. Sepkoski was also a research associate at the Field Museum of Natural History in Chicago. He died of heart failure related to high blood pressure at the age of 50.
Sepkoski is perhaps best known for his global compendia of marine animal families and genera, data sets that continue to motivate a tremendous amount of paleobiological research. Sepkoski himself explored his compendium very thoroughly. In 1981, he identified three great Evolutionary Faunas in the marine animal fossil record. Each of his Evolutionary Faunas, the Cambrian, Paleozoic, and Modern Faunas, is composed of Linnean classes of animals that have covarying diversity patterns, characteristic rates of turnover, and broadly similar ecologies. Most importantly, they sequentially replaced one another as dominant groups during the Phanerozoic. Sepkoski modeled the Evolutionary Faunas using three coupled logistic functions, but the underlying drivers of the prominent shift in taxonomic composition represented by the three faunas remains unknown.
- (1983). Charles Schuchert Award, Paleontological Society
- Elected foreign member of the Polish Academy of Sciences
Selected publications 
- Sepkoski, J. John, Jr. (1978). "A kinetic model of Phanerozoic taxonomic diversity. I. Analysis of marine orders.". Paleobiology 4 (3): 223–251. JSTOR 2400203.
- Sepkoski, J. John, Jr. (1979). "A kinetic model of Phanerozoic taxonomic diversity. II. Early Phanerozoic families and multiple equilibria.". Paleobiology 5 (3): 222–251. JSTOR 2400257.
- Sepkoski, J. John, Jr. (1981). "A factor analytic description of the Phanerozoic marine fossil record.". Paleobiology 7 (1): 36–53. JSTOR 2400639.
- Raup, David M. and Sepkoski, J. John, Jr. (19 March 1982). "Mass extinctions in the marine fossil record". Science 215 (4539): 1501–3. Bibcode:1982Sci...215.1501R. doi:10.1126/science.215.4539.1501. PMID 17788674.
- Sepkoski, J. John, Jr. (1984). "A kinetic model of Phanerozoic taxonomic diversity. III. Post-Paleozoic families and mass extinctions.". Paleobiology 10 (2): 246–267. JSTOR 2400399.
- Raup, David M. and Sepkoski, J. John, Jr. (Feb. 1984). "Periodicity of extinctions in the geologic past". Proc Natl Acad Sci U S A 81 (3): 801–805. Bibcode:1984PNAS...81..801R. doi:10.1073/pnas.81.3.801. PMC 344925. PMID 6583680.
- Sepkoski, J. John, Jr. (1988). "Alpha, beta, or gamma: where does all the diversity go?". Paleobiology 14 (3): 221–234. JSTOR 2400884.
- Sepkoski, J. John, Jr. (1996). "Patterns of Phanerozoic extinction: a perspective from global data bases". In O.H. Walliser. Global Events and Event Stratigraphy. Berlin: Springer. pp. 35–51
- Sepkoski, J. John, Jr. (2002). A compendium of fossil marine animal genera, Bulletins of American Paleontology, 364. Ithaca, NY: Paleontological Research Institution. p. 560. ISBN 978-0-87710-450-6.
Further reading 
- "Sepkoski, J. John, Jr.". American National Biography. Oxford University Press. Subscription needed.
- Miller, Arnold. (Sep. 1999). Memorial: J. John Sepkoski, Jr.: A personal reflection. Journal of Paleontology.
- NASA, Near Earth Object Program
- Sepkoski's Online Genus Database