Extinction of the Old, Evolution of the New: What really happened to the dinosaurs?

ResearchBlogging.orgMany years ago, a sudden event occurred that changed everything. Or at least, that is what we think now. But in truth, the event took longer than many today believe, and many of the specific details, the exact order of events, the actual meaning of each detail, are not fully understood. Indeed, in the process of describing this event today, we find considerable disagreement, or at least, it is clear that one person's version is different than another's. I'd be happy to give you my version of it. What qualifies me to do that? Well, for one thing, I was there when it happened...

I refer, of course to the realization that a giant object from outer space can land on the earth with catastrophic consequences, perhaps causing a mass extinction, and that this could for the first time nicely explain a strange pattern in the fossil record which, in turn, had only just then been discovered: that long periods of boring stasis were occasionally (maybe even periodically) punctuated by mass extinction events.

These realizations ... this fundamental, holistic and richly explanatory rewrite of paleontology ... happened more or less spontaneously from about 1970 to 1990. Oh, I should note: In geology, 20 years is less than an instant. (And I'm not talking about the fossil record here, but rather, the often glacial pace at which ideas set in stone are either buried or eroded into dust. Often at no great loess.)

It has been understood for a very long time that the history of life on earth can be divided into great ages during which time one or another fauna and flora dominated. The Devonian was the age of fish. We are at present in the age of mammals. The age of dinosaurs spans the Triassic, Jurassic and the (K)Cretaceous (ignore that "K" for now) which together make up the Mesozoic Era (225 to 65 million years ago). Of course, all these ages together are really the Age of Bacteria. But that is another discussion for another time.

What was not appreciated for all this geologist time (the past couple of centuries) is that very stark boundaries separated many -- maybe all -- of these time periods. The realization that this is so was famously made official by Niles Eldridge and Stephen Gould in a 1972 paper on what they called punctuated equilibira (not equilibrium). To make a long story short, during the 1970s and into the 1980s paleontologists and geologists, as well as evolutionary biologists, made an important transition; At the end of this period of intellectual history, most people accepted as very likely the idea that species evolution is rare and slow and unspectacular for long periods of time, and that these periods of relative stasis (equilibrium) are punctuated by very short periods ... geological instants ... during which there was lots of extinction. The extinction presumably caused open niches, and possibly the causes of extinction caused changes in conditions, so extinctions would be followed by lots and lots of speciation. Because something bad happened, and that bad thing may well have been a large object hitting the earth, nasty volcanism, dramatic sea level change causing the chemistry of the oceans to shift dangerously, or whatever.

In the late 1970s a large impact crater was discovered in the Yucatan. The crater became known as Chicxulub. Later on in time, a team of physicists and geologists, the core members being Luis and Walter Alvarez, made the startling observation that here and there around the earth one can find a layer different from whatever is below it, and different from whatever is above it, and that itself contains an anomalously high concentration of iridium, an element that usually shows up from outer space, and that is otherwise quite rare on earth.

So over several years, the pattern of the fossil record, based on data that had been built up over centuries, was reinterpreted to be based on a framework of sudden, major, occasional events, a giant impact crater that dated to the time of the dinosaur impact was discovered, and convincing geological evidence of a global event marking the Cretaceous-Tertiary transition ... called the KT boundary (K for Cretaceous) was identified.

Theory, data, smoking gun. Case closed.

The exact order of discovery, realization, integration, and synthesis was actually somewhat complex. My personal recolleciton is that many geologists took a long time to get on board with each of these elements. I'm pretty sure that the Alvarez Hypothesis was extant, and being taken pretty seriously, before the argument that the Chicxulub crater in the Yucatan was the impact site for this event fully took hold, but that eventually did happen.

I remember well one moment in the history of this punctuation in thinking among geologists and paleontologists. It was at a meeting of the American Association for the Advancement of Science (probably in New York). It was something that Stephen Jay Gould Said:

"Get that thing closed or tell those people to shut up ... I'm trying to give a lecture here...."

Oh, no wait, that's not it. yes, he did say that, but I was thinking of something different. Let's see (.... accessing memory banks ....) maybe this:

"No, Bernard, I do NOT give you permission to answer that question for me. I said I was not answering it and that's the end of it! It was a stupid question when asked of me and asking if of you does not change that situation one iota!"

No, wait, that wasn't it either. Let me think about this for a secon..... Oh, OK, I got it! He said:

"It is a remarkable observation of the history of science and intellectual discourse generally that what may well be the most important single fact to come to light relevant to the human endeavor, indeed to the survival of humanity itself, was gleaned from the close scrutiny and dedicated study of of the dull gray fossil record by earnest but mostly boring paleontologist working in the dusty attics and store houses of largely neglected natural history museums the world over." ... or words to that effect.

(I must say ... I actually got a headache writing that last paragraph.)

But as you probably know by now, because a lot of people have been talking about it, the case is not as closed as was once thought. After two decades of transformation of geologists and paleontologists the world over, who tend to be very conservative about their ideas (the utterly obvious idea of plate tectonics took about a half a century to fully take hold ... the first use of stable isotopes to document glacial change was in the late 1960s but the method did not become normal and accepted by everyone until the mid 1980s ... and so on), there is now evidence that the Chicxulub impact occurred 300,000 years before the KT boundary indicated by the iridium.

The evidence is actually pretty straight foward. It consists of a layer of sediment that post dates the impact and that seems to have been laid down by normal processes, over a reasonably well estimated interval of 300,000 years. The KT layer sits atop this layer.

Here is a description of this finding by the discoverer of this evidence, Gerta Keller:

The newest research ... uses evidence from Mexico to suggest that the Chicxulub impact predates the K-T boundary by as many as 300,000 years. "From El Penon and other localities in Mexico we know that between 4 and 9 metres of sediments were deposited at about 2-3 centimetres per thousand years after the impact. The mass extinction level can be seen in the sediments above this interval" says Keller.

Advocates of the Chicxulub impact theory suggest that the impact crater and the mass extinction event only appear far apart in the sedimentary record because of earthquake or tsunami disturbance that resulted from the impact of the asteroid.

'The problem with the tsunami interpretation' says Dr Keller, 'is that this sandstone complex was not deposited over hours or days by a tsunami; deposition occurred over a very long time period'.

The study found that the sediments separating the two events were characteristic of normal sedimentation, with burrows formed by creatures colonising the ocean floor, erosion and transportation of sediments, and no evidence of structural disturbance.

As well as this, they found evidence that the Chicxulub impact had nothing like the dramatic impact on species diversity that has been suggested. At one site at El Peon, the researchers found 52 species present in sediments below the impact spherule layer, and counted all 52 still present in layers above the spherules. In contrast, at a site at La Sierrita which records the K-T boundary, 31 out of 44 species disappeared from the fossil record.

"We found that not a single species went extinct as a result of the Chicxulub impact...these are astonishing results that have been confirmed by more studies in Texas" says Keller.

There are two elements in this description: 1) The sepration of the Chicxulub impact and the KT event; and 2) the relative ho-hum nature of the KT boundary itself. A third element not mentioned is that Keller suggests that a major volcanic event in India may have been the actual cause of extinction that we associated with the end of the Cretaceous.

So is this correct? I shall explain.

The separation of the Chicxulub impact and the KT boundary needs to be very firmly established, and maybe it is so established at this point. This would rule out Chicxulub as the cause of the KT event. However, this does not rule out an impact. The iridium is still there.

It might be that the 300,000 year intervening time period is not really there. This hinges mainly on a small number of geological sections that are interpreted using techniqes that are a) well established but b) not necessarily tested under all the necessary circumstances to be truly bullet proof. I myself was involved in an excavation where such evidence was used to argue for a certain sedimentary process, but under careful examination we turned out to be (probably) wrong. Things are not always what they seem in the geological record. (See: The Greg Layer.) Having said all that, I'm currently liking the 300,000 year time interval, but that is subject to revision.

Again, separating a particular crater from the KT boundary does not eliminate the impact idea, it just complicates things (in important ways).

Regarding the lack of extinction across the boundary in some places: That is interesting. This has been noted before in other areas, and in some cases the seeming lack of extinction went way when it was realized that the fossils above the boundary were actually from below the boundary, but were washed into the upper sediment (from raised-up fossil beds). Also, we expect the boundary to be imperfect ... there should be groups of organisms surviving past the boundary then going extinct later (and some, obviously, not going extinct at all). These particular cases, if verified, are not hypothesis killers, but rather, they are just reality complexifiers.

So, I conclude: The next couple of years studying this is going to be interesting. Don't you think?

The research summary quoted above can be found here.

Kim Hannula gives her perspective here.
Ethan Siegal discusses this issue here.
Suvrat Kher provides his analysis here.


This is an open access paper published a while back that will give you an excellent orientation to this work:

Keller, G. (2004). From The Cover: Chicxulub impact predates the K-T boundary mass extinction Proceedings of the National Academy of Sciences, 101 (11), 3753-3758 DOI: 10.1073/pnas.0400396101

More like this

So, how do they get the 300,000 years again? Are they assuming a rate of dust deposition that is constant? After an impact? After major climate change? After big vegetation changes, presumably? I would have thought that changing weather/ climate, maybe a big kill off of trees or grasses, could so severely alter erosion that sedimentation rates would be the least constant way of estimating an interval. (disclaimer... i know very little about geology, and nothing about the details here). Also, the Deccan traps weren't as big an eruption as say Toba, were they?

It is disturbing that Seigal seems to say that questioning a scientific consensus makes one a crackpot. It is questioning the consensus without evidence that makes one a crackpot. But Keller has evidence which is somewhat compelling. If it turns out that dinosaurs existed for hundreds of thousands of years after Chicxulub, then the consensus has some 'splainin' to do.

Lots and lots bigger, I think

By Eddie Janssen (not verified) on 06 May 2009 #permalink

About the Deccan Trapps:
"The Deccan plateau of western India is the site of another huge continental flood basalt province, occupying an area of half a million square kilometers, with an original volume generally estimated as two million cubic kilometers. The maximum thickness of 2.5 kilometers is in the Western Ghats. Little-known offshore extensions suggest that the volume might be much greater. Both magnetostratigraphic and radiometric dating indicate that the duration of the basaltic eruptions was about a million years, straddling the K-T boundary."
(Tony Hallam: Catastrophes and Lesser Calamities, Oxford 2004 page 142/143).
In his overview of the major extinctions during the last 500 million years he gives a table (on page 162) with a summary of the proposed causes of these extinctions and bolide impacts only get a probable link with the KT event.

By Eddie Janssen (not verified) on 06 May 2009 #permalink

I have not examined the evidence with the necessary fine tooth comb (it is not all available yet but should be shortly) but my understanding is that the sediments we are talking about are deltaic (or similar) sediments which exhibit the usual properties of slowly accumulating basin sediments. The particular rate of accumulation that is estimated is presumably based on models from modern day situations that are similar, in combination with some radiometric dates.

Broadly speaking, there are three kinds of sedimentation rate estimates: Continuous sediments capped and underlain by radiometric dates (best case scenario); Discontinuous sediments with radiometric dates above and below (in which case a reasonable leap of faith is needed, but it is anchored in some realty) and continuous or discontinuous sediments that are tied to only one radiometric date (below, within, or above) in which magic thinking is needed, but given the vast experience that is extant regarding these sediments, even these estimates are probably reasonable.

I'm not sure where this particular estimate stands, but one thing you can ask yourself is this: How much time do you want between the impact and the KT boundary layer to disconnect them? Is 100 years enough? 1000 years? Then reexamine the estimates to see if even conservative estimates significantly exceed your requirement. That is what is needed here.

Very interesting post! I find it most compelling that no extinction seems to have befallen species above and below the impact layer. Clearly that revelation is inconsistent with the theory that the Chicxulub impact was the main driving force behind the K/T extinction. I wish I understood better the actual geologic data that supports supports this find, however. Unfortunately my imagination fails me in predicting how to account for the massive amounts of removed sediment that would be washed back into the crater very shortly after the impact. In this way, a land impact would be a much cleaner site to investigate.

I wonder though if such impacts as Chicxulub are necessarily isolated incidents. It may be possible that a series of disturbances in an astroid field could originate from a single destabilizing influence, yielding a series of impacts over a long span of time. Is there geologic evidence that may suggest such a series of events? If that could be shown, then each impact would need to only supply a destabilizing influence on life and culminate in a protracted extinction. Clearly this would result in a prolonged deposition of materials, including iridium, to build up the K/T boundary. Unfortunately I don't know much about geology and can't do any more than pose questions about sediment layers.

Another thought occurs. It may also be possible that a massive impact, or series of impacts, may begin an unstable period in the earth's crust that may lead to tsunamis, earthquakes and vulcanism, perhaps tying the Chicxulub impact to the Deccan Trapps?

no great loess

Nice one, Centurion!

By John Scanlon FCD (not verified) on 06 May 2009 #permalink

Well, as noted it's not impossible to have an impact result in some honking great basaltic releases. Finding that crater is going to be tough!

As for the "giant meteor impact" scenario, I believe the first serious analysis was by J. E. Enever, titled "Giant Meteor Impact," Analog 1966 (I have an original copy. Suffer.) Enever's analysis was damn good; forty years later most of the current theory of major impact events is very much like his description.

Regardless of the KT Extinction, let's give the Alvarez Hypothesis credit for getting the world reasonably serious about earth-crossers. Whatever killed the dinosaurs, it wouldn't take nearly as much to end human civilization.

By D. C. Sessions (not verified) on 06 May 2009 #permalink

Is there geologic evidence that may suggest such a series of events?
There's evidence that the Boltysh and Silverpit craters were created at roughly the same time as Chicxulub. The diameter if Chicxulub is around 180km, the diameter of Boltysh crater is around 24km, and the Silverpit crater is around 3km.

Also, there's a potential crater called Shiva crater of the coast of India which dwarfs Chicxulub at about 400km by 600km. It's not widely accepted that this feature is even a crater though, let alone an impact crater.

It may also be possible that a massive impact, or series of impacts, may begin an unstable period in the earth's crust that may lead to tsunamis, earthquakes and vulcanism, perhaps tying the Chicxulub impact to the Deccan Trapps?

It has been proposed that the Chicxulub impact was the cause of the Deccan Traps. The idea is that the two places where an asteroid would do the most damage would be the site of the impact, and the point on the earth directly opposite of the impact by the antipodal effect. The main problem with this idea is that Chicxulub impact appears to have happened after the creation of the Deccan Traps was already well underway.

There's a bit of a hybrid theory that says while the Deccan traps already existed, they were just a trickle at the time of the Chicxulub impact. The shockwave from Chicxulub served to open the floodgates.

The historical background of the 'Alvarez Hypothesis' in this post is a bit muddy. For a great summary of the debates about the asteroid strike in the 1980's-1990's check out 'T.rex and the Crater of Doom." Like D.C. points out a number of paleontologists were considering extinction mechanisms like asteroid strikes, supernovas, etc. at the time, the Alvarez team just happened to be the ones to find the most compelling evidence and keep after it.

As for the Keller paper, I haven't had the chance to read it yet, but she seems to keep picking sites that have been ripped apart by the asteroid strike and can be ambiguous. People have been saying we need better sampling of global sites for years but Keller keeps sampling from sites close to the impact that are confusing to start with. I am not a specialist in geology, but I am a little suspicious of how she is going about gathering evidence for her hypothesis (i.e. doing the same things over and over again). If her hypothesis is going to be confirmed it is going to have to match evidence from sites elsewhere in the world further away from the impact site.

@Miss Cellania

I'm still trying to wrap my head around K standing for Cretaceous.

Once you've figured that one out, Question #2 on today's quiz is Why does EKG stand for electrocardiogram?

@Miss Celania

K = Cretaceous, because C = Cambrian.

#Miss Celania

Slightly longer: As davem correctly suggests it is KT rather than CT because C is the designation for the Cambrian. Depending on the source you credit the K comes from either the Greek kreta or the German Kreide. Both conveniently mean chalk, which is what Cretaceous means.

PS. I'm no geologist, but I have read Bill Bryson's '...Everything' (p.244)

Brian! Sorry I was "muddy" (though I wasn't). Yes, the actual situation over this period of twenty years, this geologist instant, was naturally far more complex than a paragraph in a blog post is going to convey. Duh.

However, it really is true that Alvarez-squared did not simply shore up thinking that was already steaming along in this direction. The whole concept of strikes as important has always waned and waxed, and it continues to do so today, and the A.H. was the first empirically linked demonstration of an extraterrestrial effect of this magnitude. You are underestimating it's impact at the time. (I deeply apologize for that pun. Totally unintentional.)

I am going to stay agnostic about the current question, but I do think there is a reason Keller is going for what she is going for. There is never going to be a way to convincingly radiometrically compare global effects from different areas. The querstion is, was this crater formed by the same object that supplied the KT boundary iridium. What she is doing is looking at the impact site exactly because that is the only way to test the relationship between events this close in time. That is basic geology. Stratigraphy and stuff. It may be messy but there is no other way to do it.

I'm not sure why people are not questioning the logic that disassociating iridium with a particular crater removes impacts as a phenomenon. It is still true that there are many sequences around the world with species below the iridium and not above. It seems that THAT is the key question right now.

Nice article but missing a connect the dots explanation. The Yucatan impact and the Deccan Traps are close to a straignt line through the core. The angle of impact and putty nature of the magma (not quite a liquid but as incompressable) and law of the conservation of energy leads me to deduce that the initial fracturing of the crust at the Deccan Traps is a direct result of said impact. Unlike the impact, the eruptions (multiple) of the Traps could easliy have been a delayed reaction and a long and continous process.

Dr. Bakker points out that the dinosauria were already in decline from about 70 mya. Coincidently there were multiple large impacts roughly 70 mya also. Call me crazy but it would appear to me that these orders were already quite stressed by the time of the KT event.

I did see your post about the traps preceding the impact but I disagree. Dating the end of an event is easy, dating the beginning somewhat difficult.

I'm not sure why people are not questioning the logic that disassociating iridium with a particular crater removes impacts as a phenomenon.

There is independent evidence linking Chicxulub to the K-T boundary such as the presence of shocked quartz and glass spherules. Volcanism can't account for that.

Might this be the one you mean?
"The enduringly popular theory that the Chicxulub crater holds the clue to the demise of the dinosaurs, along with some 65 percent of all species 65 million years ago, is challenged in a paper to be published in the Journal of the Geological Society on April 27, 2009." (see the Science Daily Article).

BTW, I am truly disappointed that no one has commented on this:

And I'm not talking about the fossil record here, but rather, the often glacial pace at which ideas set in stone are either buried or eroded into dust. Often at no great loess.

Now that everyone understands why the boundary is referred to as the "K/T" boundary, it's time to drop it and learn "K/Pg"(as in Paleogene) boundary.

- I'm disappointed that you confused punk eek with mass extinction events. Punk eek is something that's supposed to happen (and has been found to happen) at the species level; it's supposed to explain why species don't (usually) intergrade imperceptibly in the fossil record. To be fair, I think Gould is partly to blame for overblowing the rhetorics about exactly how revolutionary punk eek was.
- Keller has published a paper about the Chicxulub crater being 300,000 years older than the K-Pg boundary every year this millennium (give or take a few). Still doesn't seem to have convinced anyone else in her field, maybe because finding K microfossils in the crater doesn't mean the crater is older; in fact, it has to be expected, because the walls of the primary crater -- vertical at the top, and many kilometers high -- are expected to collapse within minutes.
- The alleged dinosaur decline in the end-K is nothing but bad statistics. Fix that, and it just disappears. A paper on this is coming out (the research was presented at the Society of Vertebrate Paleontology meeting last October).
- As someone has mentioned, the K-Pg boundary line lies between two lava flows in the Deccan Traps (and in a sediment layer at that). The main episode of eruptions was even over 100,000 years before the boundary. Obviously, the Chicxulub impact cannot have caused the Deccan eruptions.
- The Shiva "crater" is science-fiction, Christian Köberl told me. He's a geochemistry professor at the University of Vienna who has worked a lot on impact craters.
- Löss isn't pronounced the way you apparently think it is. The vowel is about the same as the one in French le and leur, and similar to the British er/ir/ur sound.

By David MarjanoviÄ (not verified) on 07 May 2009 #permalink

Ed Pardo, my link points to work from India, as I said. Your link is about the Mexican work that started this whole post.

David, you are such a pinhead. There is a link postulated between punctuated equlibria and extinction events. This is widely discussed in the literature. I have not confused them ... they are different things ... but the link between the two is .. well, if you have not understood this by now there is not much I can help you with.

Re-read my post but this time carefully. I was not joking about the historical context, and what people were saying and thinking.

in fact, it has to be expected, because the walls of the primary crater -- vertical at the top, and many kilometers high -- are expected to collapse within minutes.

I'm not in the business of defending Keller, but I do NOT expect any bones to be anything but vaporized or atomized for several kilometers (several hundred kilometers) out from this crater.

The alleged dinosaur decline in the end-K is nothing but bad statistics. Fix that, and it just disappears.

I believe that you are probably correct about that.

The main episode of eruptions was even over 100,000 years before the boundary. Obviously, the Chicxulub impact cannot have caused the Deccan eruptions.

Yes, this has been stated above, and now you stated it. Obviously this is a problem.

Löss isn't pronounced the way you apparently think it is. The vowel is about the same as the one in French le and leur, and similar to the British er/ir/ur sound.

And why would you think I would not know how to pronounce Loess? How terribly offensive of you. This is how puns often work. You really are such a pin head. You are not wrong about EVERYTYING you say, but the quality of your contribution is fully negated by your unredeemable obnoxosity.


The Deccan Traps conjecture I find intriguing because as far as I was aware, it was the second biggest volcanic event in the history of the earth that we know of, with only the Siberian Traps being bigger, and the Siberian Traps have been proposed as a possible cause of the Permian-Triassic extinction.

Even if the dissociation of Chicxulub with the K/T event holds up, like Greg said, the irridium is still there at the boundary, which suggests another giant impact? Two 10km+ impacts within 300 000 years of each other seems to me like a pretty nasty piece of cosmic bad luck. One wonders how much a ecosystem can be stressed without there being obvious evidence of mass extinction in the fossil record (populations could drop substantially while the individual species manage to hang on, resulting in no obvious extinction in the fossil record), and how vulnerable said stress could render the biosphere to a second big whack.

Even if the dissociation of Chicxulub with the K/T event holds up, like Greg said, the irridium is still there at the boundary, which suggests another giant impact?

Not necessarily. The earths core is rich in iridium, so volcanism can be a source. But the isotope ratio and distribution of iridium at the K-T boundary point towards an asteroid, and the distribution of shocked quartz and glass spherules at the K-T boundary point towards Chicxulub.

Thanks for the explanation, DaveM and Hugh. Now I will always remember both Kretaceous and Cambrian. I am also no geologist, but my father was and my daughter wants to be.

Sorry, I thought that you were referring to the pnas link which is a different paper than the one in the article I linked. I thought that you were trying to post a link (I saw the blue text and thought that it might be one). Could you try again as I would like to see where it was supposed to go.

I saw that and agreed with you hence no mention. But I also liked the Gould part in particular.

Am I wrong, or is the suggestion sort of that a major asteroid impact event didn't even produce LOCAL extinctions?

How close to ground zero are these fossil beds?

I'm having trouble being convinced if part of the story is that right around the impact site, life continued as if nothing had happened...

There is a link postulated between punctuated equlibria and extinction events. This is widely discussed in the literature.

Surprises me, because I can't see how that makes sense. I'd appreciate some references.

I'm not in the business of defending Keller, but I do NOT expect any bones to be anything but vaporized or atomized for several kilometers (several hundred kilometers) out from this crater.

Not bones â foraminifera; a major component of the rock itself. The whole story started when Keller (I think it was her) claimed to have identified Cretaceous foraminifera in the infilling of the crater and drew the conclusion that the Cretaceous continued after the crater had been formed.

I believe that you are probably correct about that.

Don't worry, I'll post the abstract soon.

And why would you think I would not know how to pronounce Loess? How terribly offensive of you. This is how puns often work.

Because to me, a native speaker of German, they don't even sound similar, so the pun simply doesn't work. :-| Evidently I've misjudged how native speakers of English hear this. Thanks, I've learned something.

Now I will always remember both Kretaceous and Cambrian.

C is for Carboniferous. :-) For the Cambrian, the stratigraphers came up with a symbol of its own; it looks like ⬠but with only one horizontal bar. It's not supported by Unicode as far as I know, and I've never seen it occurring in printed text.

By David MarjanoviÄ (not verified) on 08 May 2009 #permalink

Matthew Carrano: Patterns of diversity among latest Cretaceous dinosaurs in North America, supplement to Journal of Vertebrate Paleontology 28(3), 61A

Latest Cretaceous dinosaur diversity has been a contentious point in discussions of dinosaur extinction, resulting in widely divergent opinions of both the pattern and its relevance. At the local scale, intraformational sampling shows little evidence for a decline in dinosaur diversity immediately prior to the end of the Maastrichtian [this was published in 1999, I think; the Maastrichtian comprises the last 5 Ma of the K]. Globally, diversity is much higher in the Campanian [the preceding stage, which lasted longer] than in the Maastrichtian, leading to suggestions of longer-term decline. However, comparisons of global, stage-level diversity typically rely on temporal, rather than stratigraphic, correlations when determining how to separate and align samples. This has resulted in the tendency to lump taxa into a single "Campanian" bin, despite the fact that better resolution is frequently available regarding taxon contemporaneity. It is especially important to recognize that superposed formations (e.g. Oldman, Dinosaur Park, Horseshoe Canyon) can provide genuinely sequential diversity estimates. In addition, such comparisons must also account for variations in sampling method and density, paleoenvironment, and taxonomic ranges and resolution. When these factors are addressed, North American dinosaur diversity shows much less variation between formations and time intervals than is documented by raw, stage-level diversity counts. A significant component of diversity tracks changes in how often and how many paleoenvironments are being sampled. In North America, at least, latest Cretaceous dinosaur diversity appears to reflect more complex biotic and anthropogenic [ = sampling, I suppose] patterns, rather than a drawn-out, pre-extinction decline.

Sounded a bit more impressive in the actual presentation, but not much.

Of course, one problem remains: as far as known today, the fossil record of latest Cretaceous dinosaurs is only good enough in western North America for saying anything about changes in biodiversity.

By David MarjanoviÄ (not verified) on 08 May 2009 #permalink

And, it might be noted that North America may have been affected by this particular impact more than other regions.

I think we can hope for the African record to continue to improve over time.

Am I wrong, or is the suggestion sort of that a major asteroid impact event didn't even produce LOCAL extinctions?

Yes, at least none big enough to be noticeable.

I think we can hope for the African record to continue to improve over time.

Certainly. There's a promising Late Cretaceous site in Tanzania... though I don't think it goes all the way up to the boundary; but the point is that Africa is, for obvious historical and financial reasons, drastically underexplored.

By David MarjanoviÄ (not verified) on 08 May 2009 #permalink

Shoot a rifle bullet at a milk jug, small hole in front (localized impact effect), huge hole at rear of jug (major antipodal-lateral-climactic effect). Immediate regional extinctions around the impact would be unexpected, and are not indicated.

Impact -> much higher leakage of (pre-existing) Deccan traps at antipode -> extinction of specialized flora/fauna. Tectonically, India has a shallower crust thickness than other continents, it may have rattled quite a bit.

I don't know exactly what happened to the iridium, if it stayed in the atmosphere for a while after the impact as a gas or dust particulate.

What if the bottle is full? The best would be full of mud with a high viscosity or damp clay.

If the bottle is full than all the dinosaurs living on its surface get wet.

Maybe they did. Maybe that is why Bakker sees the decline in N.A. fauna from 70mya through the KT.

There is a parallel at the PT event and the same argument. Bedout crater impact occurs before the Siberian Traps. It was much more of an ocean impact than Yucatan and the marine extinction around 90 of species. Then later a 70% extinction of terrestrial species (just a little more then the KT event) with the eruption (and continuing flow) of the Siberian Traps on the other side of the globe.

Sorry - 90 of species should of course be 90% of species

A milk jug, as in plastic, full of milk or water. I'd guess 70ma NAmerica passed the tropics northwards resulting in reduced species diversity of 'cool' blooded animals due to poor adaptation in colder climate, while burrowing mammals handled the cold well.

The PT event sounds similar to the KT event.

Very similar but somewhat more devestating. Peter Ward did an excellent book called "Gorgon" about his research in the Karoo of Africa. The PT boundary is easily accessable there.

He did not talk about Bedout however as it was not known at the time of printing. He does talk a little about the traps however, but not very much.

If the Deccan antipode was the (terrestrial/aerial) dino killer then the PT ocean "impact" should be called ocean "explosion", since it was presumably the Siberian antipode of the Bedout impact. This would be the equivalent of the ocean floor at the antipode massively increasing output of benthic smoker vents, changing both water temperature and chemistry, and later on air temperature and chemistry.

Yes. There was another similar event as well: The Atlantic Traps. The problem is that if it was also the result of an impact, it would be very difficult to find as it would have been somewhere mid Pacific. Fascinating subject no?

Mass extinctions

@ 14 minutes: flood basalts, note the picture of Earth basalt flows, oddly symmetrical. I figure flood basalts are antipodal to comet impacts, release of gases caused mass extinctions.

There was a compendium issue of paltgonaoloey in the Anatomical Record in 2009 which included a fascinating paper by Edith Schachner showing that dinosaurs had lungs with a one-way through air circulation like birds, in contrast to the tidal air circulation that we have. The bird / dinosaur one-way system, which employs air sacs in bones, is TEN TIMES more efficient than ours. Bird lungs dont move out and in like ours with breathing. They have a rigid shape, and are smaller than ours relative to body size. But their much greater efficiency allows them to accomplish the aerobic feat of flying long distances, impossible for mammals.That dinosaurs also had these bird-like lungs (birds are of course dinosaurs, the surviving or crown group) means that they literally would have RUN RINGS AROUND any mammalian ancestors that they encountered. The more agile ones like the struthiomimids and raptors would probably have run indefinitely without tiring. Thus our thecodont ancestors had to sit out 150 million odd years as nocturnal rats waiting for the dinosaurs to go away.Our ancestors had to sit through three or four mass extinctions in fact before our moment came. The biggest was the Permian-Triassic, a heat event. Flood basalt eruptions in Siberia realised the wildest AGW dream-nightmare of catastrophe, with prolonged massive volcanism and atmospheric discharge resulting in warming leading to catastropic ocean anoxia, almost total extinction in the sea and 80-90% on land. However two groups that survived, Therapsids and Thecodonts, developed into the dinosaurs and (eventually) mammals respectively. The dinosaurs were well heat adapted, especially with their efficient lungs. So the mammalian precursors lost out but did not die out.The next catatrophe was also a heat event, the Triassic Jurassic, basically the start of the separation of America from Europe-Africa, and the opening up of the mid-Atlantic ridge. Again big-time volcanism, acute warming. Again the dinosaurs did well. (But we held on.)However During the cretaceous, a general cooling started. Also there were cold snaps (as the dinosaurian BBC would have called them) such as the one described in this article from Plymouth. This began to stress the dinosaurs who preferred it hot. This may be one reason why some dinosaurs tended to larger size in the Cretaceous like T Rex. (Although sauropods were big in the Jurassic). So some good news for the rat-like mammals-in-waiting.Then came the end-Cretaceous disaster, the Chikxulub meteor impact. Finally a cold event extinction. The dinosaurs perished except the dinosaurian ancestors of the birds. Mammals with their fur and thermoregulation survived, and, following brief competition with some monster-chicken like bird predators, emerged finally as the dominant land animals.Climate continued to cool in the Tertiary further playing to mammals' advantages. Eventually the current glacial period developed (landmass surrounding a north polar sea).But if AGW is correct and CO2 release reverses 200 million years of cooling, then maybe the tide will turn again? Perhaps the birds will evolve back into dinosaurs?A major physiological advantage of dinosaurs over say humans relates to playing the organ. A human organist has a balance problem, he uses feet for the pedal bass notes and hands for the keyboard,and leans forward with no counter-weight. A dinosaur, realising development toward bifocal eyes, opposing thumbs and intelligence etc.. (e.g. Struthiomimus, Compsognathus etc.) would not have this problem. The leg and arm claws, though fewer in number (3-4 rather than 5) would still play the pedals and keyboard effectively, and the tail would counter-balance the whole organist. Thus the complete realisation of Bach's musical creativity awaits this significant climate warming and consequent re-adjustment of life-forms.