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Re: paleontolgist, dinosaur



From: John Bois <jbois@umd5.umd.edu>
 > If we are still using Archibald's data, the only group which falls into
 > your stated range (75%-90% extinction) is the marsupials.  And we don't
 > need an extra-terrestrial cause to dispatch them--placental replacement
 > is a parsimonious hypothesis for this.

Considering that marsupial diversity is high in even the latest of the
Lancian mammal faunules, I would say that this hypothesis is contrary
to the data. (All Lancian mammalian faunas have several species of
didelphids alone, not to mention the non-didelphid marsupials).
Competitive replacement is almost always slow, not rapid.

Thus, Archibald's data shows a rather rapid loss of 75-80% of the
marsupial fauna of the Lancian in passing into the Puercan. This is
clearly more consistant with the near loss of marsupials in NA being
related to the mass extinction as a whole.

 > > Are you suggesting thast NONE of the suggested causes was involved?
 > WHY DINOS? ...
 >
 > > ... Together there is a synergistic effect
 > > that amplifies the individual effects.
 >
 > Why Dinos?

Sheer bad luck.  They just happened to all succumb due to stochastic
repsonse factors.  That is why I say that the overemphasis on the
100% loss of dinosaurs is improper.  All heavily hit groups, both
terrestrial and marine, need to be consideed in evaluating the causes
of the extinctions. This should be done without worrying about the
relatively trivial detail of 100% versus 80%.

 > One species of snail is a poor example.  We know stochastic factors
 > singly or in tandem can cause isolated effects.  ...

The difficulty in studying natural, as opposed to anthropogenic,
extinctions, is that most currently living organisms are heavily
influenced by human behavior.

  >because it got cold
 > (or hot) now all the babies were of one sex_, or my own favorite:
 > _dinosaurs were non-stealthy egg layers ...
 >
The problem is that this is *too* specific.  It fails to account for
the whole pattern of extinctions.

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

The peace of God be with you.