Joseph John Sepkoski Jr. (July 26, 1948 – May 1, 1999) was aUniversity of Chicagopaleontologist. Sepkoski studied the fossil record and the diversity of life on Earth. Sepkoski andDavid Raup produced a new understanding ofextinction events, by developing a statistical approach to the study of taxonomic diversification. They suggested that theextinction of dinosaurs 66mya was part of a cycle of mass extinctions that may have occurred every 26 million years. But their most important contribution was the identification of the "Big 5" mass extinctions, events that have shaped the evolution of life on earth.
Sepkoski was born inPresque Isle, Maine. In 1970, Sepkoski received a B.S. degree,magna cum laude, from theUniversity of Notre Dame. UnderStephen Jay Gould he earned a Ph.D. in geological sciences fromHarvard University in 1977. His Ph.D. was on the field geology and paleontology of theBlack Hills ofSouth Dakota. From 1974 to 1978, Sepkoski taught at theUniversity of Rochester. In 1978, he joined the University of Chicago and became a professor in 1986. Sepkoski was also a research associate at theField Museum of Natural History in Chicago. He died of heart failure related tohigh 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 greatEvolutionary 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 thePhanerozoic. Sepkoski modeled the Evolutionary Faunas using three coupledlogistic functions, but the underlying drivers of the prominent shift in taxonomic composition represented by the three faunas remains unknown.
Sepkoski was married to paleontologistChristine Janis, a specialist in fossil mammals. His son (from a previous marriage) is the historian of scienceDavid Sepkoski.
