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.)
