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Re: paleontolgist, dinosaur
On Wed, 13 Nov 1996, Stan Friesen wrote:
> From a statistical point of view there is not really that much
> difference between 80% extinction and 100% extinction. And there
> *were* several other terrestrial groups that showed 75-90% extinction.
> It may well have been essentially accidental that non-avian dinosaurs
> suffered 100% extinction instead of 90%.
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.
> Are you suggesting thast NONE of the suggested causes was involved?
> I am skeptical of this as at this point almost all imaginable causes
> have been considered (even highly unlikely ones), and, as you say,
> none. by themselves, really matches to the pattern of victims and
> survivors. This is why I say that none alone can do the job - no
> one factor would produce the observed pattern.
Life is played out on the environmental stage. Phylogeny is the result
of unfathomably complex causes and effects. Everything has to do with
everything else. I agree that the environment has influence especially
in times of stress. My only point is that it is still not enough to
invoke multifarious environmental influences as the killer(s) if you
don't say HOW they killed. Other organisms lived yet suffered the
same viscicitudes. WHY DINOS?
> Simple, each factor produces its own set of stresses on the various
> species. Each, alone, would cause a few extinctions, and also shuffle
> the ranges of the remainder. Together there is a synergistic effect
> that amplifies the individual effects.
> Not too long ago Stephen Jay Gould wrote a short essay on the recent
> exctinction of a snail that used to live in the sea grass beds off the
> Atlantic coast...
One species of snail is a poor example. We know stochastic factors
singly or in tandem can cause isolated effects. But what we are
confronted with in dino extinction is a _pattern_. What did all dinos
have in common such that they all, in all places (if that is true),
died. As I said before, this is a proximate/ultimate cause problem.
Satisfactory proximate causes include the ones you have mentioned. But
acceptable ultimate causes must be of the order of: _all dinos were above
a certain mass which was unsupportable due to lack of photosynthesis_, or
_all dinos determined sex of baby by temperature and because it got cold
(or hot) now all the babies were of one sex_, or my own favorite:
_dinosaurs were non-stealthy egg layers and suffered at the hands of new
and old species_. Whatever. Or, we can sit back and say the truth:
there were many ecological perturbations around that time, but, exactly
why the dinos died out we just don't know.