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Extinction thoughts (yes, some more :-)



This is a re-send.

Allan Edels 

-----Original Message-----
From: Allan Edels [mailto:edels@msn.Com] 
Sent: Tuesday, July 16, 2002 3:21 AM
To: 'jbois@umd5.umd.edu'; 'dinosaur@usc.edu'
Subject: Extinction thoughts (yes, some more :-)

HP John Bois (et al):

I think we all can agree that birds as we know them survived the K-T
boundary - at least in sufficient numbers to still be around today.  

We can all agree that the majority of the pterosaurs disappeared many
millions of prior to the end of the Cretaceous.  

We can all agree that all of the non-avian dinosaurs disappeared BY the
end of the Cretaceous.  (Plus or minus a few possibles).

I think it is safe to say that we can all agree that the flora and fauna
changed dramatically - culminating in the end of the Cretaceous.   

I believe most people can agree that something large hit the earth at
the end of the Mesozoic.  The size of the bolide and the amount of
damage caused by may be debated, but its existence SEEMS sure.

The type of PURELY competitive supplanting of the non-avian dinosaurs as
proposed by HP Bois has never been documented before or since.  This
requires some sort of extraordinary triggering mechanism.  Too many
clades disappeared at once (geologically speaking :-)) to explain it by
only competition.  The statistical anomaly of so many clades
disappearing within a short time frame (again, geological time) requires
some additional methods above and beyond the normal background local
species extinction reasons - i.e. competition, disease, environmental
changes, etc.

I agree that the survivors of the K-T end-time out-competed the other
animals.   I merely suggest that the rules of competition were
drastically changed by the bolide, thereby enabling the successful
out-competition of the dinosaurs and other non-survivors. All of the
normal pressures still existed - but ALL were intensified by the new
constraints due to the changes in the environment - brought about by the
bolide.

For the edification of younger list members, it is important to remember
the theories of the K-T extinctions PRIOR to the bolide idea.  All of
the ideas that HP Bois has presented (at least in a gross, overview
version) had been presented and debated for decades, with very little
agreement.  Lots of questions remained unanswered by the "standard"
theories.  

Then Carl Sagan and others proposed the "Nuclear Winter" hypothesis - as
a warning against the use of nuclear weapons in a major confrontation.  

The Alvarezes (Luis and Walter) extended that idea to begin the path to
our current understanding of what a bolide strike might cause, based on
finding an Iridium spike in K-T clay sediments in many locations
worldwide.  (Around 1980).  The predicted results seemed too good to be
true [all sorts of problems present in the other competing theories
seemed to be solved] - besides, where was the crater?  NOW we know that
something around the size of the predicted bolide hit the earth at
Chixulub (Mexico), at the right time.

I used to believe that the impact was the sole causal agent in the K-T
extinction.  Many people have complained that the effects of the bolide
are too many - too deadly and too widespread to allow the existence of
almost ANY vertebrate life!  IF all of the effects of the bolide
occurred with maximum force, then I would agree.  However, if all of the
effects occurred in varying levels of efficacy, then the environment
would be changed sufficiently to allow the differential survival rates.
Today I see the bolide as the major causal agent, triggering or enabling
several other processes to take effect, creating the extinctions that we
see.  

Bottom line, IMHO: Is the extinction of the non-avian dinosaurs (and
several other clades) the action of the usual competition that somehow
all culminated at the same time? Or did the bolide strike change enough
of the environment so that features of the various survivors that were
once merely of minor importance, became essential to survival, enabling
them to out-compete the others who didn't have those features?  I think
you know my answer.

Allan Edels