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Re: paleontolgist, dinosaur



From: John Bois <jbois@umd5.umd.edu>

 > On Thu, 7 Nov 1996, Stan Friesen wrote:
 > > > 1. What is your theory about how the dinosaurs got extinct?
 > > 
 > > A combination of causes occuring in a geologically short time period
 > > combined to drive them to extinctions.  Some of the main contributors
 > > were:
 > >    1. The volcanic eruptions forming the Deccan Traps in India.
 > >    2. The lowering of sea levels to nearly as low as they now are.
 > >    3. The impact of a giant meteorite, perhaps in the Yucatan
 > >    4. Possibly (little evidence available as yet), an large
 > >       decrease in the oxygen content of the oceans (oceanic anoxia). 
 > 
 > These are events, not causes.  How did they drive all dinos (big and 
 > small) to extinction  while leaving many other terrestrial lineages 
 > unaffected.  Archibald's Montana data shows the following % species 
 > survivorship:

The volcanic eruptions probably effected global climate, and perhaps
induced extensive acid rain wrold-wide.

The lowering of sea levels changed climates from maritime to continental
over lare areas, reduced the extent of continental shelf (contributing
to the *marine* extinctions), and perhaps reduced the habitat variety
on land as well.

The effects of the impact have been well covered elsewhere.

The interesting thing is that ??Archibald's data (in the recent book on
the extinctions) is, according to him, more in line with causation by
the Deccan volcanism than by an impact. (If I remember correctly he
concludes that no one single cause quite matches observed pattern of
extinctions - which also supports my multi-causal model).

And, oh, if the oceanic anoxia turns out to be real, the effects on
marine shelf zone life should be obvious. I suspect that the changes
in mineral and oxygen cycling might also effect climate and land
ecology (by changing the limiting resources for plant growth, for
instance).


Here is another bit of evidence:
Amoung all of the various mass extinctions, and near-mass extinctions,
the most commonly co-occuring events are oceanic anoxia and flood basalt
volcanism such as produced the Deccan traps. (For instance, the Permo-
Triassic extinctions are associated with oceanic anoxia, two different
flood basalt zones, and extreme low sea levels, not to mention the
continental glaciation).

swf@elsegundoca.ncr.com         sarima@ix.netcom.com

The peace of God be with you.