Paper 35 - R. Kiat

Paper 35: Raup and Sepkoski , 1982 – by Rebecca K.

Raup, D. M., & Sepkoski, J. J. (1982). Mass extinctions in the marine fossil record. Science, 215(4539), 1501-1503.

Commentary by Jessica Theodor

David M. Raup

-        Professor of Paleontology at the University of Chicago (before retiring)

-        PhD from the Harvard University

-        Passed away in 2015

David M. Raup - Excerpts from the New York Times:

“He used to say he went into paleontology because it was a field with a lot of data that no one was analyzing,” his wife said in an interview.

As an author and theorist, Dr. Raup raised questions about extinction patterns and biodiversity.

Dr. Raup challenged the conventional view that changes in diversity within major groups of creatures were continuous and protracted, and advanced the theory that such changes can be effected by random events.

And he questioned the accepted notion that biodiversity — that is, the number of extant species — has vastly increased over the past 500 million years, pointing out, among other things, that because newer fossils embedded in newer rock are easier to find than older fossils in older rock, it is possible that we simply have not uncovered the evidence of many older species whose existence would undermine the theory. His conclusion, that the data of the fossil record does not allow the unambiguous presumption that biodiversity has increased, has profound implications.

Dr. Raup’s most famous contribution to the field may have been the revelation in 1983, after a six-year study of marine organisms he conducted with J. John Sepkoski Jr., that over the last 250 million years, extinctions of species spiked at regular intervals of about 26 million years.

J.John Sepkoski Jr

-        Professor of Paleontology at the University of Chicago

-        PhD from the Harvard University

-        Passed away in 1999

J.John Sepkoski Jr - Excerpts from the New York Times:

''No one had ever done it before,'' said Dr. Stephen Jay Gould, a paleontologist at Harvard University who was Dr. Sepkoski's graduate school adviser. ''He compiled a completely consistent data set on all groups, terrestrial, marine, single-celled, multicelled, animals and plants, everything.''

Dr. Sepkoski's most important finding, researchers say, was the discovery of what appears to have been three distinct faunas, each dominating hundreds of millions of years in the fossil record, patterns never before documented or even proposed by others.

''Jack was the first one to recognize those,'' said Dr. Douglas Erwin, a paleobiologist at the National Museum of Natural History at the Smithsonian Institution. The effort, Dr. Erwin added, prompted considerable follow-up research by others.

''In the 80's, when I was in graduate school,'' he said, ''his work influenced what most people did, what most people were thinking about.''

Paper Summary:

            In this paper, Raup and Sepkoski provide us statistical evidence for what is now commonly known as the Big Five mass extinctions. By compiling a large, global dataset from the marine fossil record, Raup and Sepkoski demonstrated the extinction rate (per million years) through time for marine invertebrates and vertebrates that were divided based on families (Fig. 1). There were four distinct extinction events that stood out as statistically significant and well above the baseline extinction rates; these five extinctions occurred in the late Ordovician, Permian, Triassic and Cretaceous. There is also the late Devonian which although appeared noticeable, was not statistically significant - the authors later argue that this is likely due to either sampling error (smearing of extinctions as they are distributed over two stages) or an extinction event that was dragged on over a longer period of time. Fig. 1 also shows that background extinction rates has decreased over recent geological time.

Another figure in the paper, Fig. 2, demonstrates the number of families of marine invertebrates and vertebrates over time. The magnitude of the abrupt drops in the diversity curve during the five extinctions is important to consider as it shows how much percentage of marine diversity was loss during these events (note: although not significant in Fig 1., Fig. 2 shows a substantial drop in diversity during the late Devonian extinction). From Fig. 2 it can also be seen that overall marine diversity has increased in recent years.

Although these extinctions had been recognized before this, it wasn’t solidly established throughout the literature, nor had been statistically proven, especially with such a comprehensive dataset – which is definitely a hallmark of the paper with using a mass quantitative approach to paleontology. The paper also demonstrated the magnitude of these extinction events, as well as the how quickly they occurred as extinctions events repeated in geologic time.

Notes & Questions:

1)    Was ‘shelly’ a references to invertebrates with exoskeletons?

2)    Would we be able to go through the methods in class? For example, I’m not sure I follow what is meant by lower resolution series-level data when they talk about making modifications.

*I came across an article by one of the authors, Sepkoski, called “Extinctions of Life”. I found it to be a useful general guide to understanding paleontology (background and methods) better in light of this paper, specifically: https://fas.org/sgp/othergov/doe/lanl/pubs/00285846.pdf

*Another more ‘recent’ paper which discusses marine diversity with microbial carbonates in particular if anyone might be interested: http://www.robertriding.com/pdf/riding2006mc.pdf

(Riding, R. (2006). Microbial carbonate abundance compared with fluctuations in metazoan diversity over geological time. Sedimentary Geology, 185(3), 229-238.)