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Re: _Night Comes to the Cretaceous_



In a message dated 98-08-07 20:01:57 EDT, jbois@umd5.umd.edu writes:

<< From what I have read Alvarez suffers from a too facile assuredness of his
 own opinions. >>

Well, perhaps. But so what? Does this, by itself, make his opinions wrong?
 
<< The best evidence we have suggests, and you seem to agree, that non-avian
 dinosaurs were becoming less diverse anyway.  As Horner says, its like the
 passenger pigeon extinction: who cares what killed the last pigeon.  If
 she died from a cold would anyone say passenger pigeons became extinct due
 to the cold virus? >>

I think that non-avian dinosaurs were indeed becoming less diverse, but they
were a long(!) way from going extinct by the end of the Cretaceous.They were
hardly down to the last individuals of each species; they were still running
the place, with forms such as _Tyrannosaurus_, _Triceratops_, and numerous
other Maastrichtian genera worldwide. We're definitely not talking about
killing the last passenger pigeon here. Also, our available K-T-boundary
dinosaur samples suffer heavily from an indeterminable amount of Signor-Lipps
effect, so just how less diverse--if this is in fact the case--is not easily
measurable.

<<Such explanations trivialize what is an enormously complex process.
Often (usually) extinctions have many contributing causes.  As
Leigh Van Valen says, most times attributing an extinction to one cause
rather than another can be just a matter of taste.  For example, during
the making of the Panama Canal, when the flooding of hills formed hill-top
islands, several bird species became extinct.  The apparent mechanism for
this was complex.  Whether because big cats migrated off the now too-small
range, or because of reduced hunting, small carnivorous mammals underwent
a population explosion.  They preyed the birds into extinction.  What
caused the extinction?  Habitat fragmentation? Mammal predation?  A
less-than-optimal-nesting strategy?  Now, there is every reason to suspect
multiple causes at and before the K/T.  In my view, pointing at one
particular cause just because you have some evidence which _might_
correlate, is poor science.  >>

Well, background extinctions have a multitude of contingent explanations, of
course. Indeed, it is this fact that makes a mass extinction so strange: How
could all those different extinctions, with all those different, complex
causes, just happen to coincide and line up so that the whole shooting match,
on all continents everywhere at once, vanishes? I think it's even more
unlikely than that birds evolved flight from the ground up.

Finally, where is it written that >all< extinctions must have a complicated
explanation? Sometimes, I dare say, the explanation is >trivial<: the earth
was smacked by a 15-mile-wide comet nucleus, and almost all the animals and
plants were roasted. That's that. We're not explaining >all< extinctions via
impacts, just one--the big one at the K-T boundary.