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Re: Impact only a part of it all....



Art Greenwalt wrote:
> 
>   While you raise good questions one of the problems with the idea of the
> dinosaurs already being on the way out was that just prior to the KT
> boundary the ceratopsians seem to be flourishing, from what I understand.  I
> believe the hadrosaurs were also extending their speciation and seemed to be
> doing well as a group.

That would seem to be the hallmark of a "good" extinction, though,
wouldn't it...those animals which have already been weakened by
competition with the newer species, those that are specialized, those
that are simply evolutionary dead ends, they would be the ones to be
effected.  As far as I know, the ceretopsians were a very adaptable
group, as their succeess was showing.  Ditto for the Hadrosaurs.  I
wonder if being ground grazers had something to do with this...?

>     Everytime I think of the KT boundary and meteoric impact I come back to
> the problem of why some species died and some didn't, why all the dinosaurs
> went including those on their last lineage legs and those fresh and
> vigorous, why the large marine reptiles pretty much died out...and so
> forth.  There is such an odd selectivity at the KT boundary with the birds
> surviving nicely, turtles making it through, crocydilians, yet dinos going
> away so abruptly that it is real hard to to reconcile the survival and
> non-survival with just one event such as the irrefutable meteor impact.

Do we have any info at all on marine reptiles in the open ocean, rather
than just the inland seas?  I would guess (and please bear in mind, I am
really just an enthusiastic amateur) that most of the marine reptiles we
know of are from the shallow inland seas that eventually dried up due to
continental drift (what about ice caps...were any forming at the tail
end of the Cretasceous, which might also lock up oceanic water?).  Early
birds may have been beating out the flying reptiles, which weren't as
adaptable.  If I remember right, the Pterosaurs were already in a
decline.  But you are right indeed, why should nearly all of the large
animals die out.  And, I suppose, it is really not just the large
animals...there were still plenty of small dino species around, smaller
than some crocodilians.  Why then should they have died out, but the
Crocs didn't?

>    Though very much an amateur in this area, I suspect it will turn out to
> be a multiplicity of factors which by coincidence (after all, that's what
> coincidence is all about) hit pretty much at the same time to produce this
> odd selection of extinctions.  Keep in mind when we look at the KT boundary
> we're not seeing an extremely fine time-scale here.  Even events spread out
> over several thousand years would not be distinguishable within that layer,
> at least with our present data.

Is there a fairly good estimate of how long the KT extinction took? 
I've heard everything from a few million years to less than one
hundred....

> ....Art, in Alaska...

best regards...
-- 
John M. Dollan
Montana State University-Northern
Graduate Assistant
http://www.geocities.com/Athens/Academy/1861/
ICQ# 308260

"To make an apple pie from scratch, you must first create the
universe...."  Carl Sagan