Mass Extinctions and Their Aftermath
by A Hallam and PB Wignall
Catasrophes and Lesser Calamities
by Tony Hallam
Let me start with saying that these books are good. They are both readable works and quite fun for the paleontologist wannabe to follow along. If you are looking for the lower bar, ie easier read, than you are looking for the second book. It is the more recent and slightly more up to date, but not nearly as detailed. The first book is delightfully chalk full of technical jargon and details though.
There is also a nontrivial bias in both books. Hallam is a marine paleontologist. His view of mass extinctions is based from that stance. What may or may not have happened on the land at times is glossed over. While the first book gives lists of what happened to various groups at each of the Big Five mass extinctions, it is uber biased towards marine fossils.
There are good reasons for this in the sense that the marine record is going to be far better than the terrestrial. However, the glossing over of some of it is really annoying. The PT Boundary was a good example, really. The marine is extensively discussed, but the terrestrial is not. Very annoying.
The books do a good job of discussing the events that surround the mass extinctions. This includes the competing theories, observed behavior of the fossil record, some illusions that can happen with respect to said record, and how life rebounds. One of the more interesting things to note is that people tend to focus on the so-called Big Five mass extinctions: The Ordovician, Devonian, Permian, Late Triassic and Cretaceous. In the latter book, it was pointed out that these are merely the biggest ones and that they are really just the tail end of a curve as far as the distrubition goes. They are not really that unique except in size which captures the imagination. Especially the PT and KT events.
Hallam is also very much a fan of one of the possible explanations for mass extinction and it shines through some in the coauthored work and very brightly in his solely authored work: that theory is of sea level rise and fall (marine transgressions, anoxia, and regression). The Rise, fall, and anoxia combo makes sense when you consider the point of view of the marine critters. New, very energetic (ie not deep and full of sunlight) areas are opened up. Marine critters love it and explode into them. These environments go away or are drastically reduced (a la the Cretaceous) and we end up with a lot of species competing for drastically reduced resources. If the deep waters are anoxic...it gets worse. However, the question remains about how much this effects the terrestrial ecosystems.
The possible causes that are covered by the two books are pretty few, but the evidence for and against is presented. The ever favourite bollide impacts are one of the possible causes, but interestingly there seems to be only one event that is pretty much confirmed to be directly related (KT Event). The FF extinction during the Devonian /might/ be related, but the Kellwasser is not. The Kellwasser of the Devonian, various Ordovician, and Late Triassic events are all pointing to the sea level and anoxia combo beloved by Hallam. Global Climate change seems to stand up as the winner for the PT Event. The former book gives a nice detailed list of what went extinct for each event. Nicely they also give evidence for and against each theory at each point. Interestingly, vulcanism is indicted for the PT event but through belching CO2 and /warming/ the planet. Surprisingly, vulcanism has had very little impact otherwise. In some other posts I will be talking about each event. However the books do have some other interesting points.
There are some effects that are intersting that ought to be discussed. The first is the Signor-Lipps Effect. This is where the fossil record gives the impression due to the way the fossils are laid down that an extinction event is gradual rather than abrupt or catastrophic.
Another interesting tidbit that I'd heard about that cause interesting problems for identifying extinction events are the Lazarus and Elvis Taxa. The Lazarus taxa are those that seem to die out and go missing from the fossil record for a very long time. They return after they repopulate from a refuge that had a been not giving a good fossil record. Alternately, the Elvis Taxa are the ones that evolve into a form that is very close to the one that died out. They're so named because they're immitating the original form very closely and can cause confusion to the unwary paleontologist: much like all the Elvis impersonators. This is less of a problem for vertebrates than others I would think. There are other classifications as well the obvious extinct ataxa, holdover taxa, progenitor and disaster taxa round out the list.
In addition, there's been some intriguing work that has been touched on here about the survival of the dinosaurs past the KT event. It's logical that some would have lingered on a bit, but there was a bit in Mass Extinctions about teeth from Hell's Creek that were above the KT line (but might have been reworked, actually probably were) and in Catastrophies (the latter book) there was some information out of China about the same possible scenario. In googling there may be some of the same evidence in the San Juan Basin in New Mexico. It's an interesting and exciting prospect that throws lots of cold water on theories if true...but most likely these fossils have simply been reworked. We shall see.
The details of the different isotopic analyses are also available. This is in Mass Extinctions. It gives a very good run down about what each isotope that is sought means and why. the isotopes that are looked for are carbon, sulphur, oxygen, strontium, and iridium.
Mass Extinctions covers a lot of smaller events than the Big 5. There numerous others that they go through. They're interesting in that they detail smaller ones and their causes as well. It recaps with the major causes for when the book was written at the end. Catastrophies touches on the 6th Mass Extinction...the one caused by humanity. it pokes some serious holes in things. A favourite quote is...
pg 199. [emphasis added]
They're good books. I believe Mass Extinctions and Their Aftermath to be the superior one even though it is older. Catastrophes and Lesser Calamities is a lighter and easier read though. Both are filled with a lot to chew on though! It's heavy material from the point of view of serious thought.
Over the next week (I hope) I'll be posting comments on each of the mass extinctions.
by A Hallam and PB Wignall
Catasrophes and Lesser Calamities
by Tony Hallam
Let me start with saying that these books are good. They are both readable works and quite fun for the paleontologist wannabe to follow along. If you are looking for the lower bar, ie easier read, than you are looking for the second book. It is the more recent and slightly more up to date, but not nearly as detailed. The first book is delightfully chalk full of technical jargon and details though.
There is also a nontrivial bias in both books. Hallam is a marine paleontologist. His view of mass extinctions is based from that stance. What may or may not have happened on the land at times is glossed over. While the first book gives lists of what happened to various groups at each of the Big Five mass extinctions, it is uber biased towards marine fossils.
There are good reasons for this in the sense that the marine record is going to be far better than the terrestrial. However, the glossing over of some of it is really annoying. The PT Boundary was a good example, really. The marine is extensively discussed, but the terrestrial is not. Very annoying.
The books do a good job of discussing the events that surround the mass extinctions. This includes the competing theories, observed behavior of the fossil record, some illusions that can happen with respect to said record, and how life rebounds. One of the more interesting things to note is that people tend to focus on the so-called Big Five mass extinctions: The Ordovician, Devonian, Permian, Late Triassic and Cretaceous. In the latter book, it was pointed out that these are merely the biggest ones and that they are really just the tail end of a curve as far as the distrubition goes. They are not really that unique except in size which captures the imagination. Especially the PT and KT events.
Hallam is also very much a fan of one of the possible explanations for mass extinction and it shines through some in the coauthored work and very brightly in his solely authored work: that theory is of sea level rise and fall (marine transgressions, anoxia, and regression). The Rise, fall, and anoxia combo makes sense when you consider the point of view of the marine critters. New, very energetic (ie not deep and full of sunlight) areas are opened up. Marine critters love it and explode into them. These environments go away or are drastically reduced (a la the Cretaceous) and we end up with a lot of species competing for drastically reduced resources. If the deep waters are anoxic...it gets worse. However, the question remains about how much this effects the terrestrial ecosystems.
The possible causes that are covered by the two books are pretty few, but the evidence for and against is presented. The ever favourite bollide impacts are one of the possible causes, but interestingly there seems to be only one event that is pretty much confirmed to be directly related (KT Event). The FF extinction during the Devonian /might/ be related, but the Kellwasser is not. The Kellwasser of the Devonian, various Ordovician, and Late Triassic events are all pointing to the sea level and anoxia combo beloved by Hallam. Global Climate change seems to stand up as the winner for the PT Event. The former book gives a nice detailed list of what went extinct for each event. Nicely they also give evidence for and against each theory at each point. Interestingly, vulcanism is indicted for the PT event but through belching CO2 and /warming/ the planet. Surprisingly, vulcanism has had very little impact otherwise. In some other posts I will be talking about each event. However the books do have some other interesting points.
There are some effects that are intersting that ought to be discussed. The first is the Signor-Lipps Effect. This is where the fossil record gives the impression due to the way the fossils are laid down that an extinction event is gradual rather than abrupt or catastrophic.
Another interesting tidbit that I'd heard about that cause interesting problems for identifying extinction events are the Lazarus and Elvis Taxa. The Lazarus taxa are those that seem to die out and go missing from the fossil record for a very long time. They return after they repopulate from a refuge that had a been not giving a good fossil record. Alternately, the Elvis Taxa are the ones that evolve into a form that is very close to the one that died out. They're so named because they're immitating the original form very closely and can cause confusion to the unwary paleontologist: much like all the Elvis impersonators. This is less of a problem for vertebrates than others I would think. There are other classifications as well the obvious extinct ataxa, holdover taxa, progenitor and disaster taxa round out the list.
In addition, there's been some intriguing work that has been touched on here about the survival of the dinosaurs past the KT event. It's logical that some would have lingered on a bit, but there was a bit in Mass Extinctions about teeth from Hell's Creek that were above the KT line (but might have been reworked, actually probably were) and in Catastrophies (the latter book) there was some information out of China about the same possible scenario. In googling there may be some of the same evidence in the San Juan Basin in New Mexico. It's an interesting and exciting prospect that throws lots of cold water on theories if true...but most likely these fossils have simply been reworked. We shall see.
The details of the different isotopic analyses are also available. This is in Mass Extinctions. It gives a very good run down about what each isotope that is sought means and why. the isotopes that are looked for are carbon, sulphur, oxygen, strontium, and iridium.
Mass Extinctions covers a lot of smaller events than the Big 5. There numerous others that they go through. They're interesting in that they detail smaller ones and their causes as well. It recaps with the major causes for when the book was written at the end. Catastrophies touches on the 6th Mass Extinction...the one caused by humanity. it pokes some serious holes in things. A favourite quote is...
The sombre picture outlined above should dispel once and for all the romantic idea of the superior ecological wisdom of nonWestern and pre-colonial societies. The notion of the noble savage living in harmony with Nature should be despatched to the realm of mythology where it belongs. Human beings have never lived in harmony with nature.
pg 199. [emphasis added]
They're good books. I believe Mass Extinctions and Their Aftermath to be the superior one even though it is older. Catastrophes and Lesser Calamities is a lighter and easier read though. Both are filled with a lot to chew on though! It's heavy material from the point of view of serious thought.
Over the next week (I hope) I'll be posting comments on each of the mass extinctions.
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