K/T Impact: support from an analysis of recovry and productivity!

[happy_Alex]

Play along with me for a bit here, while I ask some akward questions...


I'm not disputing that the meteorite hit the earth and that it was one of many over history, I also am not disputing that it caused massive disruption to ecosystems. I am just asking whether it really caused the extinction of the dinosaurs, or whether they were on the way out for other reasons. For example we know that there was no gradual decrease in diversity of dinosaurs before the KT event. However, this fact does not in itself imply that an asteroid caused extinction. If you look at the dinosaurs of this period such as the ceratops, their designs were becoming more outlandish yet perhaps this indicates that dinosaurs had stopped evolving in any other significant sense and were becoming uncompetitive in comparison to mammals. The grey squirrel is only marginally more effective than the red squirrell yet the presence of the former in the UK has caused a precipitous decline of the latter.

In short, why look towards meteorites for casues of extinction when there are more plausible evoloutionary mechanisms?

Also, not all the fossil evidence is consistent with the Alvarez hypothesis. For example, moths survived through the extinction, requiring a)clean air to breath, inconsistent with the dust laden air following the impact and b) pollen to feed, inconsistent with no flowering plants following a meterite winter.

Also, other cold blooded species survived. And although there were no animals 'larger than a cat' to survive, there were a) dinosaurs smaller than a cat (Compsognathus).

The OT demonstrates a ecosystem of increased dependance on detritus feeding animals and subsequent food chains. However, why does this imply that a) dinosaurs could not already fit into this food chain and b) were unable to adapt.

 

[carlosMM]

I am just asking whether it really caused the extinction of the dinosaurs, or whether they were on the way out for other reasons. For example we know that there was no gradual decrease in diversity of dinosaurs before the KT event. However, this fact does not in itself imply that an asteroid caused extinction. If you look at the dinosaurs of this period such as the ceratops, their designs were becoming more outlandish yet perhaps this indicates that dinosaurs had stopped evolving in any other significant sense and were becoming uncompetitive in comparison to mammals. The grey squirrel is only marginally more effective than the red squirrell yet the presence of the former in the UK has caused a precipitous decline of the latter.

As you already noted, there was no decline. Your squirrel example is not applicable for a simple reason: both species are extremely similar. OTOH, a mammal the size of a rat is extremely different from a 7 ton dinosaur. Therefore, the slow (per amount of difference) change you see in outcompeting squirrels is something that can be expected in stable ecosystems, or those changing at 'background' rate, but for Cretaceous mammals to outcompete dinosaurs requires massive changes.

Also, 'outlandish' is not a useful criterion. I for one can say that locomotory adaptations in late Cretaceous dinosaurs are highly specialized and that their ornamentation etc. is no less and no more elaborate than what is seen today in birds and mammals. You are basically arguing, if you refuse the hypothesis of a massive ecosystem change (which, remember, coincides with a giant meteorite impact), from the point of 'genetic senility', a concept that is absurdly false.

In short, why look towards meteorites for casues of extinction when there are more plausible evoloutionary mechanisms?

Please name one that can do this much damage in such a short time, across such a wide range of ecosystems on land, in the air, and in the sea. And, btw, in fresh water, too. Worldwide.


Just one, please?

Also, not all the fossil evidence is consistent with the Alvarez hypothesis. For example, moths survived through the extinction, requiring a)clean air to breath, inconsistent with the dust laden air following the impact and b) pollen to feed, inconsistent with no flowering plants following a meterite winter.

Now you are making what I call a mental short-circuit! NOTHING survived close to the impact site. But it takes just two moths, on the other side of the world, to survive. Just two. And a handful of annuals with seeds that can rest a few years before germination.

Your short-circuit is that you assume that a local (albeit extreme) event has worldwide effects ONLY. It has both local and worldwide consequences.

Now, obviously we need to clarify one thing here: nobody claims that the rock hit, and WHAM BAM all dinos keeled over dead. Next day, the sun rose and everything was fine. No sir, this no work.

Instead, the scenario is this: locally, 100% died. Further away,
a) a large percentage of individuals of all spceies died immediately or soon, from direct and indirect influence,
b) long term consequences hindered population recovery in most species
c) more long term consequences and 'background' processes together weed out many taxa.

Also, other cold blooded species survived.

Dinosaurs were endtherm homeotherms with four chambered hearts and (saurischia) unidirectional lung ventilation.

And although there were no animals 'larger than a cat' to survive, there were a) dinosaurs smaller than a cat (Compsognathus).

C. did not live at that time.
Also, small dinosaurs survived! And plenty are around today. What a coincidence!

The OT demonstrates a ecosystem of increased dependance on detritus feeding animals and subsequent food chains. However, why does this imply that a) dinosaurs could not already fit into this food chain and b) were unable to adapt.

it does not say anything about dinoaurs directly. It does say, however, that in marine systems, a massive sudden disruption happened, consistent with an event, not a process. 'event' meaning 'way too fast for adaptation by anybody', 'process' means 'slow or rapid change that can stir up a lot, but may allow adaptation'.



More? I love this topic; I said as a kid what today is scientific consensus, and for the right reasons by the way, crocs are a good key to understanding the K/T extinction pattern - wanna know?

 

[The Last Conformist]

If you look at the dinosaurs of this period such as the ceratops, their designs were becoming more outlandish yet perhaps this indicates that dinosaurs had stopped evolving in any other significant sense and were becoming uncompetitive in comparison to mammals. The grey squirrel is only marginally more effective than the red squirrell yet the presence of the former in the UK has caused a precipitous decline of the latter.

In short, why look towards meteorites for casues of extinction when there are more plausible evoloutionary mechanisms?

To suggest that ceratopsians were out-competed by mammals is absurd - there simply were no mammals that could compete with them at the time. To suggest that every dinosaurian group was out-competed by mammals at the same time is ... well, absurder.This coincidentally happening just at the time as most marine species bite it seems like more than stretching it.

As for Compsognathus, that particular critter was some 80 Ma dead by the end Cretaceous. Other small dinosaurs did survive - we call them birds.

 

[Eran of Arcadia]

Remember, boys and girls, "dinosauria" as most people understand it, is a paraphyletic clade . . .

 

[The Last Conformist]

As most people understand it, "dinosaur" means big extinct lizard. Luckily palaeontology isn't a democracy.

 

[carlosMM]

Remember, boys and girls, "dinosauria" as most people understand it, is a paraphyletic clade . . .

Well, can't blame the scientists for ignorance in the general public - the nonsense is taught in schools, to begin with. There's been many an attempt to get the dreadful 'reptiles' out of school curriculums, but no chance. And so on.

 

[carlosMM]

Bleh, I am shocked to see that my prestigious university does not (no longer ?) have an online subscription to Geology. Annoying, now I'll have to walk over to the lib, copy and scan it. DOH!

Bast, do send me your email, if you want a copy.

 

[happy_Alex]

I found an interesting article on the subject here
http://io9.gizmodo.com/5241410/new-evidence-suggests-an-asteroid-couldnt-have-killed-the-dinosaurs

which talks about a 2009 study that seems to show extensive continuity of species after the timeline that the asteroid impact was supposed to have occurred, for example an estimate from the authors that 300,000 organisms continued after the impact- so if the impact was powerfull to knock-out dinosaurs how were organisms across the spectrum able to survive? It wasn't a "smart" asteroid!

 

[Gori the Grey]

I think an asteroid may have hit this thread ten years ago and life is just starting to make its way back.

 

[Ajidica]

*checks for RD status*
*realizes thread is over a decade old, so pre-RD and pre-Chamber Pot*

 

[Berzerker]

I read a recent article suggesting the impact generated quakes in the 6-7 range in Colorado.

 

[Lexicus]

Interesting! If anybody wants it I can get the PDF the next time I am in the office. Martin Aberhan is a cautious man, but the way I read the abstract it means that there really was a massive (I should rather say MASSIVE) disturbance of the food chain right at the K/T boundary. Mark another one for the impact theory!

So I'm curious, are there other ways this data can be explained? How is this not equally consistent with, say, the volcanic eruption theory?

I'm asking as someone with something of an emotional attachment to the impact theory. It's also my understanding that the extinction may have had multiple causes.

EDIT: I didn't realize this thread was so old. Instead of asking OP then, consider that I'm asking anyone who might know.

 

[carlosMM]

So I'm curious, are there other ways this data can be explained? How is this not equally consistent with, say, the volcanic eruption theory?

Well, remember that all the data has a huge uncertainty in it when compared to an impact event. So, if you really stretch the time windows as much as you can, you may end up with enough ambiguity to talk not about a few years of direct effect but decades, or even a century or two. And then, maybe, you can come up with a so-far-unknown process of making volcanic eruptions happen at a rate 1000 times higher than anything known to geology.....
oh yeah, I know a way of doing that!

Imagine you hit earth really, really hard, jostle everything really good. Like, with a giant sledgehammer. Obviously, and weak place in the crust would let go: earthquakes would be triggered all over, volcanoes would erupt, the entire system would just spew stuff at every crack!

Now, what might happen that's comparable to that imaginary giant sledgehammer?

Oh, right: a huge meteorite impact!

On a more serious note: No, I have absolutely no confidence in the volcanism theory. For one thing, whenever and wherever we are able to get a sharp picture of what happened at the boundary, the picture is one of sudden, catastrophic change across all habitats. The observed pattern of extinction and survival fits very nicely with the known consequences of a huge impact, but would require a series of extreme unusual circumstances if volcanism was the perpetrator. And evidence for that is totally lacking: the Deccan Trapps were a huge, but drawn-out affair.
Where is the ONE global volcanic ash layer, the ONE global flood basalt? You'd need that, and it ain't there! We do have the ash layer, but it is choke full of iridium, and goes along with lots of signs of cataclysmic change: tsunami deposits, clasts from halfway around the world, etc. You can't get this from seeping-like-water eruptions of basaltic lava, and for the initial phase to be so uniform and sudden we simple lack any explanation or proof in the field.

 

[Birdjaguar]

Even after 10 years Chicxulub still happened.

 

[Arakhor]

Moderator Action: Resurrecting ten-year-old threads is not the done thing. Start a new thread to discuss matters if you wish.