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Re: dino extinction
> can weaken a species, but the coup de grace will be delivered by some other
In regard to the "coincidental multi-causal" idea, what are some
opinions and critiques of D. Raup's kill curve of extinctions? He plotted
all extinctions on a graph (with number of species going extinct on the
Y axis, I can't remeber waht the x-axis was) that made a nice, smooth
curve. In other words, the history of life is not a nice, mellow
sequence of species popping off occaisionally at diffeent times,
punctuated by sharp spikes of rare, huge extinctions that kill off a
bunch of everybody, but rather that there are all sizes of extinctions
and the larger the extinction, the more rare it is. He likened it to how
people generally have averge days, with occaisional bad days, and rarely
real bad days, just on the likelyhood of a certain NUMBER of crappy
things happening to you coincidentally in the course of 24 hours (at
least, thats what I think he meant-its been a while since I read his book).
If mass extinctions are the result of a bunch of
factors that are all, or mostly, going on ALL THE TIME coinciding at once,
this makes sense, with the "really bad days" being big mass extinctions,
with a bunch of things happening at one, with decreasing "bad days"
(smaller and smaller mass extinctions) coinciding less and less factors.
Even if one factor only weakens a species, the more bad luck you stack on, the
more likely you are to reduce numbers even more. (for example, reducing
populations with a drought, then stacking on an epidemic of a nasty new
disease from Asia, then hitting them with the asteroid. Each factor
adds insult to injury and reduces the likelyhood of recovery. On a not
so bad day, you might only get the disease, which would increase the
likleyhood of recovery).
However, statistical studies based on the fossil record seem
to be extremely ambiguous due to the incompleteness of the fossil
record. I doubt Dr. Raup had the resources to conduct a thourough census
of every fossil assemblage on earth, so fossil preservation sampling
error is likely to be furhther aggravated by his limits on his time and
resources. I am wondering if anyone has anything to say about the validity of
For global rather than local mass extinctions that affect whole
different phylums, I think "big picture" things like an asteroid impact
or world-wide climate change, altering currents and weather patterns and
such, are more likely to cause such a world-wide catastrophie. I think
epidemics would be a more likely factor on a regional scale, _limited_ to a
more closely related group.