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RE: (extinction)




On Fri, 5 Jul 2002, Williams, Tim wrote:

> I object to the term 'targeted' - as if marsupials and neornithines were
> prancing around with bulls-eyes on their backs.  "Look, there's one!" cries
> a flying fragment of bolide.

Gimme a non-teleological word that does the job, then.  Blind selection,
perhaps...The bolide blindly selected the extinction of marsupials because
they were hyperallergic to dust.

> In other words, differential survival does not necessarily imply any
> selective targeting mechanism.

Says who?  Are you seriously suggesting dinosaurs were unlucky--that they
experienced extinction and that this had nothing to do with their size,
niche components, whatever?  I think you would be the first.  Or, are you
just saying: OK, dinosaurs bit it because they were somehow susceptible,
but everything else was just unlucky and this proves that the bolide did
it.  If you accept dino susceptibility, you must accept marsupial, and
enantiornithine susceptibility too--in principle, at least.  OK, I agree
that it doesn't "necessarily" imply a targeting mechanism, but neither can
you say the reverse.  That is, marsupials and enantiornithines may or may
not have been blindly selected.  The only thing that gives your hypo
predominance is that it happened, and so did the bolide, so the bolide
must have done it.  But this is circular.

> And tell me, 'cause I really want to know: How you *know* that neornithines
> and placentals everywhere were unaffected by the impact?

I don't know...and didn't say it (I don't think--shouldn't have, anyway).

>  Perhaps
> neornithine and enantiornithine populations both plummeted at the end of the
> Cretaceous, but enough neornithines survived to carry the clade into the
> Paleocene (and beyond).

This, without a blind selection mechanism, is fanciful (see below).

> All you need is a dozen pairs of randy chickadees
> to get the ball rolling again.

Here are the stakes: if molecular estimates are right, you need a dozen of
many neo clades and less than a dozen of all enantiornithine clades.  I
understand that this is controversial--but it _is_ an active issue...and
the argument here rests on the resolution of _that_ argument.

> > But, as you know, exactly who were the bird survivors of the K/T is 
> > still a hot topic. 
> 
> Asked and answered.  The neornithines survived.  I can't see how this is at
> all controversial. 

I meant: which neornithine species made it through is still a hot topic.