35. Raup, D.M. and J.J. Sepkoski. 1982. Mass extinctions in the marine fossil
record. Science 215:1501-1503.
Blog Author: Ben Clinch
Blurb Author: Jessica Theodor
-BS, Palaeontology, University of Toronto, 1989
-PhD, Palaeontology, University of California at Berkeley, 1996
-Professor, Ecology & Evolutionary Biology, University of Calgary
-Research focuses on understanding the causes of organismal diversity patterns found over geologic time
Paper Author: David M. Raup
-BS, University of Chicago
-PhD, Geology, Harvard University
-Curator and Dean of Science at Field Museum of Natural History in Chicago
-Taught at Caltech, Johns Hopkins, University of Rochester
-Passed away in 2015
Main Question: Can we identify specific mass extinctions more accurately and comprehensively?
Background:
-Mass extinctions have been previously identified, but timing and magnitude of these events have proven difficult due to the fragmentary nature of fossil record data
-Previous familial data sets have been subjective due to taxonomic problems and stratigraphic imprecision
Assumptions:
-Family-level data assumed to be ideal compromise between sampling limitations and taxonomic uncertainty
Methods:
-Data set of marine vertebrates, invertebrates, protozoans from the Phanerozoic
-Data contains around 3300 fossil marine families, 2400 of which are extinct
-87% of extinctions resolved to stratigraphic stage, most resolved to stratigraphic series
-Plotted rates of extinction against geologic time (76 points) (Fig. 1)
-Linear regression ran for all 76 points of the graph: four points fell above 99% confidence interval, one point fell above 95% confidence interval
-Phanerozoic diversity curve compiled from familial data (Fig. 2)
Results:
-Two rates of extinction identified in the Phanerozoic: background extinction, mass extinction (points considerably higher than the background)
-Five mass extinctions clearly defined from data: Late Ordovician, Late Devonian, Late Permian, Late Triassic, Late Cretaceous
-Background extinction rate has declined over time
Conclusions:
-The decrease in extinction rate could be due to the theory that fitness optimization through evolutionary time leads to prolonged survival
-Decline in extinction rate during the Cambrian shows that the number of extinctions that did not occur was close to the amount of increase in diversity over that interval- suggests that the net increase in diversity throughout the Phanerozoic may have more to do with a decrease in extinction than an increase in origination
-Major mass extinctions have been identified as distinct from background extinction
-Data doesn’t inform what caused the extinctions
Questions/Comments:
-What does he mean by “the data benefit from compilation of taxonomic and stratigraphic investigations far beyond traditional sources”?
-What are “shelly” and “rarely preserved taxa”? Why didn’t he define these?
I don't know how I feel about the optimization of fitness hypothesis as a way to explain decreased background survival. I would really like to discuss it because I go back and forth in agreeing with it or not. The net increase in diversity makes more sense to me. The greater number of species that diverge, the greater the chance that one or several of those species will survive.
ReplyDeleteIt is interesting to read the paper that formalized the five mass extinction events and created the popular figure of diversity over geological time.
ReplyDeleteI wonder how consistent are the results with other taxonomic ranks given that families are somehow arbitrary defined (e.g. some families might originated from a common ancestor 15 million year old, while others might have done from 30 my).
Ben, your question about rarely preserved taxa is answered in the author's footnote (#8) at the end of the paper. I expect that shelly taxa are those with a calcium carbonate shell.
ReplyDeleteThe background extinction rate of 8 per million years is so amazing to me. The species that evolve are so incredibly well-suited to their environments. Life's incredible!
I like the distinction between diversity caused by a decrease in extinction rate rather than an increase in diversification. Not sure where to go with this comment, but this point stood out to me.
Going off of Maria's last point, I think the distinction allows for finer resolution of ecological or environmental interpretations. A decrease in extinction would suggest a stable environment, since species are staying stable and not going extinct, or continual adaptation at a steady rate. On the flip side, an increase in diversification is caused by much different processes that would cause new adaptations, morphologies and eventually new species. *Note, I wrote a longer comment and then accidentally signed out instead of posting so this is a paraphrasing of myself ha*
ReplyDeleteWhen reading the paper I was trying to get to the part where the author would explain what caused the mass extinctions. But there is none. However, I agree with the author that a cause shouldn't be inferred from this data.
ReplyDeleteI like figure 2 showing the diversity of families over geological time showing 5 extinction periods. However, I am usually skeptical about the low diversity records in earlier time. It looks like we are having the highest diversity and is it because excavation is easier towards the surface so more fossils found in recent period or something else? This is an interesting paper that mostly focuses on the data and analysis. I think these data points are interesting.
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ReplyDeleteI agree with Augi (sorry of that is wrongly spelled). It also came to my mind: if recent fossil would probably be easier to dig and find than recent fossils, can it be just that what his data is showing? Maybe paleontologist have more critical methods to analyze this that I am not aware of, but I would like to discuss that in class. Also, as Alex mentioned, that hypothesis sound weird to me, I would like to hear more about that in class too.
I feel like this paper could have been better. It wasn’t horrible since it did explain there is a qualitative difference between major mass extinctions and background extinctions, but I would have liked to know at least what stresses caused these occurrences. I feel like they did a good job point out data points in their graphs and how it aided them in their results. Overall, not the worse read, but would like extra questions answered.
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