Paper 35: "Mass Extinctions in the Marine Fossil Record" - Raup & Sepkoski (1982)
Blurb Author: Jessica Theodor
Dr. Theodor is an Associate Prof. of Ecology & Evolutionary Biology at the University of Calgary. Her research interests encompass the causes of organismal diversity patterns over geologic time; of which she uses ungulates as they are generally pretty diverse today and have an excellent fossil record.
Paper Authors: David Raup & J.J. Sepkoski Jr.
David Raup was a paleontologist at the Field Museum in Chicago widely credited with bringing evolutionary biology and statistical modeling into the field. He also found evidence for the so-called ~26-Myr extinction cycles, which have been proposed to have been caused some regular periodicity of non-ecological events like bolide impacts (though this sentiment isn't universally beloved today). Some of his former grad students include John Alroy, Mike Foote, and Charles Marshall, all prominent paleobiologists. He passed away from pneumonia in 2015.
J.J. Sepkoski was also a famous paleontologist from the Chicago area (Though he was at UChicago). His work on taxonomic diversity throughout the Phanerozoic has led to the "Sepkoski Curve" (Fig. 2) as well as his compendium of Phanerozoic marine taxa which took 10 years to complete. He received his Ph.D. from Harvard under the advisement of Stephen Jay Gould in 1977, and went on to publish several papers relating to diversity through time, including the idea of the ~26-Myr extinction cycles with Raup. His work was also paramount into helping form the Paleobiology Database (PBDB), which has helped other scholars answer standing questions about diversity through time. He died from heart failure arising from high blood pressure in 1999.
Paper Cliff Notes:
This paper showed that mass extinctions in the marine realm were definitely a thing and that they had happened multiple times throughout the Phanerozoic. Out of the so-called "Big 5" mass extinctions, this paper would rather categorize them as the "Big 4". The end-Devonian extinction was not statistically significant from the background extinction rate, partially due to the fact that it was categorized by lower rates of origination and it happened over multiple stages, potentially giving the possibility of a sampling bias. This is despite the fact that standing diversity drops across this boundary about as much as the end-Ordovician and K-Pg mass extinctions. Another conclusion that the paper made is that the background extinction rate has decreased through time. This is potentially explained by the general increase in diversity through time or the idea that species have become better adapted to their environments over geologic time. However, this could be potentially caused somewhat by the "Pull of the Recent" taphonomic bias.
Question: Do you still classify the end-Devonian extinction event as a mass extinction, or is it better explained as a "biodiversity crisis"?
Dr. Theodor is an Associate Prof. of Ecology & Evolutionary Biology at the University of Calgary. Her research interests encompass the causes of organismal diversity patterns over geologic time; of which she uses ungulates as they are generally pretty diverse today and have an excellent fossil record.
Paper Authors: David Raup & J.J. Sepkoski Jr.
David Raup was a paleontologist at the Field Museum in Chicago widely credited with bringing evolutionary biology and statistical modeling into the field. He also found evidence for the so-called ~26-Myr extinction cycles, which have been proposed to have been caused some regular periodicity of non-ecological events like bolide impacts (though this sentiment isn't universally beloved today). Some of his former grad students include John Alroy, Mike Foote, and Charles Marshall, all prominent paleobiologists. He passed away from pneumonia in 2015.
J.J. Sepkoski was also a famous paleontologist from the Chicago area (Though he was at UChicago). His work on taxonomic diversity throughout the Phanerozoic has led to the "Sepkoski Curve" (Fig. 2) as well as his compendium of Phanerozoic marine taxa which took 10 years to complete. He received his Ph.D. from Harvard under the advisement of Stephen Jay Gould in 1977, and went on to publish several papers relating to diversity through time, including the idea of the ~26-Myr extinction cycles with Raup. His work was also paramount into helping form the Paleobiology Database (PBDB), which has helped other scholars answer standing questions about diversity through time. He died from heart failure arising from high blood pressure in 1999.
Paper Cliff Notes:
This paper showed that mass extinctions in the marine realm were definitely a thing and that they had happened multiple times throughout the Phanerozoic. Out of the so-called "Big 5" mass extinctions, this paper would rather categorize them as the "Big 4". The end-Devonian extinction was not statistically significant from the background extinction rate, partially due to the fact that it was categorized by lower rates of origination and it happened over multiple stages, potentially giving the possibility of a sampling bias. This is despite the fact that standing diversity drops across this boundary about as much as the end-Ordovician and K-Pg mass extinctions. Another conclusion that the paper made is that the background extinction rate has decreased through time. This is potentially explained by the general increase in diversity through time or the idea that species have become better adapted to their environments over geologic time. However, this could be potentially caused somewhat by the "Pull of the Recent" taphonomic bias.
Question: Do you still classify the end-Devonian extinction event as a mass extinction, or is it better explained as a "biodiversity crisis"?
I'm not sure if I buy the idea that background extinctions have decreased through the Phanerozoic. At first glance, I would agree with the authors that this is just an issue of the "Pull of the Recent." But maybe I don't know enough about fitness levels through time -- are fitness levels higher through time for everyone, or just for each species during its lifetime? Another way of asking this question is, has the average lifespan of species gone up through the Phanerozoic? I may ask about this in class, I'm sure you guys have more to say about it.
ReplyDeleteI'd still like to classify the end-Devonian extinction as a mass extinction -- only because "The 5 Mass Extinctions" sounds a lot catchier than "The 4 Mass Extinctions - and maybe a Mass Depletion."
I don't feel qualified at all to speak of mass extinctions but could the low species and diversity of the Devonian have more to do with the taphonomy?
ReplyDeleteA "Biodiversity crisis" kind of screams to me that the animals that were there were not well suited to their environments, implicating that there were so many niches they could have filled but didn't. As we all know, a jelly fish has looked like a jelly fish for billions of years. why mess with what works?
My point is that perhaps the Devonian was one of the more stable geological times that allowed more species to live more or less at equilibria with the environment so most of the forms that lived during the time stayed relatively unchanged? Were conditions more stable back then?
I'm glad that Agathe pointed that out... Decrease in extinction rate due to optimization of fitness? I don't know if I would go that far... This is a big generalization/assumption... Also, we might have talk about that already but has anyone reanalyzed the significance of these 5 mass extinctions? Is the late Devonian mass extinction statistically significant today with new (more) data available?
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