Jack Sepkoski

Last updated

Joseph 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 66 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.

Sepkoski was married to paleontologist Christine Janis, a specialist in fossil mammals. His son (from a previous marriage) is the historian of science David Sepkoski.


Selected publications

Further reading

Related Research Articles

Extinction event Widespread and rapid decrease in the biodiversity on Earth

An extinction event is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. It occurs when the rate of extinction increases with respect to the rate of speciation. The number of major mass extinctions in the last 440 million years are estimated from as few as five to more than twenty. These differences stem from disagreement as to what constitutes an extinction event as "major", and the data chosen to measure past diversity.

Macroevolution Evolution on a scale at or above the level of species

Macroevolution in the modern sense is evolution that is guided by selection among interspecific variation, as opposed to selection among intraspecific variation in microevolution. This modern definition differs from the original concept, which referred macroevolution to the evolution of taxa above the species level.

Paleontology The scientific study of life prior to roughly 11,700 years ago

Paleontology, also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch. It includes the study of fossils to classify organisms and study their interactions with each other and their environments. Paleontological observations have been documented as far back as the 5th century BCE. The science became established in the 18th century as a result of Georges Cuvier's work on comparative anatomy, and developed rapidly in the 19th century. The term itself originates from Greek παλα, ὄν, and λόγος.

Permian–Triassic extinction event Earths most severe extinction event

The Permian–Triassicextinction event, also known as the End-Permian Extinction and colloquially as the Great Dying, formed the boundary between the Permian and Triassic geologic periods, as well as between the Paleozoic and Mesozoic eras, approximately 251.9 million years ago. It is the Earth's most severe known extinction event, with the extinction of 57% of biological families, 83% of genera, 81% of marine species and 70% of terrestrial vertebrate species. It was the largest known mass extinction of insects.

David M. Raup was a University of Chicago paleontologist. Raup studied the fossil record and the diversity of life on Earth. Raup contributed to the knowledge of extinction events along with his colleague Jack Sepkoski. They suggested that the extinction of dinosaurs 66 mya was part of a cycle of mass extinctions that may have occurred every 26 million years.


Paleobiology is an interdisciplinary field that combines the methods and findings found in both the earth sciences and the life sciences. Not to be confused with geobiology, which focuses more on the interactions between the biosphere and the physical Earth.

Background extinction rate, also known as the normal extinction rate, refers to the standard rate of extinction in Earth's geological and biological history before humans became a primary contributor to extinctions. This is primarily the pre-human extinction rates during periods in between major extinction events.

<i>Rugoconites</i> Extinct genus of invertebrates

Rugoconites is a genus of Ediacaran biota found as fossils in the form of a circular to oval impression preserved in high relief, six or more centimeters in diameter. The fossils are surrounded by frills that have been interpreted as sets of tentacles. The bifurcating radial ribs, spreading from a central dome, serve to distinguish this genus from Palaeophragmodictya, and may represent the channels of the gastrovascular system. Fossils of Rugoconites have been interpreted as early sponges although this is countered by Sepkoski et al. (2002), who interpreted the organism as a free-swimming jellyfish-like cnidarian; similar to Ovatoscutum. However, the fossil is consistently preserved as a neat circular form and its general morphology does not vary, therefore a benthic and perhaps slow-moving or sessile lifestyle is more likely. Ivantstov & Fedonkin (2002), suggest that Rugoconites may possess tri-radial symmetry and be a member of the Trilobozoa.

The Ordovician radiation, or the Great Ordovician Biodiversification Event (GOBE), was an evolutionary radiation of animal life throughout the Ordovician period, 40 million years after the Cambrian explosion, whereby the distinctive Cambrian fauna fizzled out to be replaced with a Paleozoic fauna rich in suspension feeder and pelagic animals.

John Alroy is a paleobiologist born in New York in 1966 and now residing in Sydney, Australia.

Olson's Extinction was a mass extinction that occurred 273 million years ago in the early Guadalupian of the Permian period and which predated the Permian–Triassic extinction event. It is named after Everett C. Olson. There was a hiatus and a sudden change in between the early Permian and middle/late Permian faunas. Since then this event has been realized across many groups, including plants, marine invertebrates, and tetrapods.

The concept of the three great evolutionary faunas of marine animals from the Cambrian to the present was introduced by Jack Sepkoski in 1981 using factor analysis of the fossil record. An evolutionary fauna typically displays an increase in biodiversity following a logistic curve followed by extinctions.

Mesozoic–Cenozoic radiation The third major extended increase in biodiversity in the Phanerozoic

The Mesozoic–Cenozoic Radiation is the third major extended increase of biodiversity in the Phanerozoic, after the Cambrian Explosion and the Great Ordovician Biodiversification Event, which appeared to exceeded the equilibrium reached after the Ordovician radiation. Made known by its identification in marine invertebrates, this evolutionary radiation began in the Mesozoic, after the Permian extinctions, and continues to this date. This spectacular radiation affected both terrestrial and marine flora and fauna, during which the “modern” fauna came to replace much of the Paleozoic fauna. Notably, this radiation event was marked by the rise of angiosperms during the mid-Cretaceous, and the K-Pg extinction, which initiated the rapid increase in mammalian biodiversity.

The Pull of the Recent describes a phenomenon in the fossil record, that causes past biodiversity estimates to be skewed towards the modern taxa, modern biodiversity being the best sampled. Diversity estimates, since Sepkoski's, have consistently shown a global increase in biodiversity since the Cambrian. The cause of this, according to the Pull of the Recent is due to favourable sampling by taphonomic processes of more recent fossils, as well as the ease of studying extant taxa.

Diversification rates are the rates at which new species form and living species go extinct. Diversification rates can be estimated from fossils, data on the species diversity of clades and their ages, or phylogenetic trees. Diversification rates are typically reported on a per-lineage basis, and refer to the diversification dynamics expected under a birth–death process.

Charles Richard Marshall is an Australian paleobiologist and the director of the University of California Museum of Paleontology, where he is also a professor in the department of Integrative Biology at the University of California, Berkeley.

Capitanian mass extinction event extinction event around 260 million years ago

The Capitanian extinction event was an extinction event that occurred around 260 million years ago during a period of decreased species richness and increased extinction rates in the late Middle Permian during the Guadalupian epoch. It is also known as the end-Guadalupian extinction event because of its initial recognition between the Guadalupian and Lopingian series; however, more refined stratigraphic study suggests that extinction peaks in many taxonomic groups occurred within the Guadalupian, in the latter half of the Capitanian age.

<i>Leucocephalus</i> Extinct genus of mammal ancestors

Leucocephalus is a genus of biarmosuchian belonging to the family Burnetiidae dating to the Wuchiapingian. It was found in the Tropidostoma Assemblage Zone (Tropidostoma) of the Main Karoo Basin of South Africa. It is a monotypic taxon which contains one only species, Leucocephalus wewersi. The genus name Leucocephalus is derived from Greek. Leucos, meaning white; kephalos, meaning skull, as the Leucocephalus skull discovered was unusually pale. Wewersi comes from the farm employee who found the skull, Klaus ‘Klaasie’ Wewers.

Linda Ivany is a professor in the Earth Sciences department at Syracuse University. Her research focuses primarily on paleoecology and paleoclimatology. She completed a BS degree in Geology at Syracuse University, and then went on to do an MS at the University of Florida-Gainesville, and a Ph.D. at Harvard University under the guidance of Stephen J. Gould. She worked at the University of Michigan 1997 - 2000, before being hired as a visiting assistant professor at Syracuse University later in 2000. She was promoted to full professor in 2012. She was involved in two seminal papers on large-scale diversity patterns in the Phanerozoic, in which the authors showed that it was very important to correct for the "completeness" of the fossil record, and showed that the increase in taxonomic diversity across the past 540 million years is not as dramatic as had been suggested by Jack Sepkoski and others.

Paleontology or palaeontology is the study of prehistoric life forms on Earth through the examination of plant and animal fossils. This includes the study of body fossils, tracks (ichnites), burrows, cast-off parts, fossilised feces (coprolites), palynomorphs and chemical residues. Because humans have encountered fossils for millennia, paleontology has a long history both before and after becoming formalized as a science. This article records significant discoveries and events related to paleontology that occurred or were published in the year 2020.