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Re: Dinosaur Extinction: Impact vs Volcanoes

Determining extinction from evolution in the fossil record is difficult 
to say the least. In the case of the late cretaceous, we see rapid 
speciation, and the rise of new groups of vertebrates. 

For example, Mosasaurs are marine lizards related most closely to 
snakes, and monitor lizards. In the last 20 million years of the 
cretaceous these lizards originated, and divided into roughly 4 families 
with numerous species originating as well. As suddenly as they appear, 
they disappear at the K/T boundary. 

Although dinosaurs are the most recognized of the animals suffering 
extinction, they make poor models of what exactly happens during an 
extinction. They are sporadically preserved, and there simply is not 
enough material to actually use to theorize with. It is hard to say what 
was happening in their evolutionary history at this point in time, 
although there are those who think they can. 

Now, what am I talking about? In the latest cretaceous, some animals 
show a decline, while others show expansion. This leads to the conundrum 
of what is exactly happening. Can we have decline and diversification at 
the same time? The answer is yes.

The nature of the fossil record( this is my area of study for those 
interested) is based wholly on presentational bias. In the case of the 
dinosaurs, they are terrestrial dwelling animals, and therefore are less 
likely to be preserved. This is because conditions do not favor 
preservation on land, as think about an animal dying in a forest, does 
it get covered quickly enough to be preserved? Probably not. 
However, In the marine environment, constant detritus and the likes are 
perpetually raining down on the sea floor. This tends to cover animals 
quickly, thereby preserving their skeletons.

So to think about it more clearly, if it was not preserved, does not 
mean that it was not there. Extinction is best gauged by marine species 
decline and disappearance. In the latest cretaceous most marine species 
were doing fine, then suddenly gone. This is how we know there was an 
extinction.

Now about the volcanic hypothesis, and dinosaur relation. This idea is 
most likely wrong. As stated above dinosaurs are preserved sporadically, 
and therefore have a bias in the fossil record. If this gradual decrease 
is apparent in the marine record, then we would have to rethink the 
impact theory. 
As for dinosaurs, it seems as though they went on diversifying until the 
end, and the environments which best preserved their skeletons were not 
as common. 

Did an impact do in the species that went extinct at the end of the 
cretaceous? I don't know. I have my doubts based on the fossil record. 
However, I tend to steer clear of this debate, as I am not thrilled 
about rehashing same data sets, and ideas. 

Could a volcano form tektites? I don't' know. People have discussed this 
before, and say no. About all I can say bout it is, it  would seem hard 
to get shocked quartz from a volcanic explosion. If a mechanism can be 
shown to generate shocked quartz in a volcano, then we might have an 
answer.  

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