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Re: Dinosaurs to birds



At 01:16 AM 1/24/99 -0500, John Bois wrote:
>OK.  But this is absolutely hypothetical, right?  Whereas I can use the
>fossil record to show trends in extinction and possible adaptations that
>influenced those trends, can you show any evidence to support your
>hypothesis of luck?

I never actually said it was my hypothesis, I was only pointing out that it
is a viable hypothesis.  (Actually, it is Gould's idea, not mine anyhow).

But at least *some* component of luck seems inescapable in mass
extinctions, since there *is* evidence that selective processes act
differently during such times.

>> In addition, many sorts of stress have an unpredictable aspect to them.
>> Even in areas otherwise stripped of life by the Mt. St. Helen's explosion,
>> there were small, protected sites where a few plants (and presumably
>> animals) survived.  Presence in such spots is certainly largely a matter of
>> accident.
>
>OK to Mt. St. Helens.  And OK to the idea.  But there is no evidence of
>any kind connecting any event to any extinctions at the K/T!

Hmm, so you deny the evidence for a bolide impact being involved?
I chose Mt. St. Helen's as a small scale model of the sort of things that
might happen after a bolide impact.

>  Again, why
>is luck being advanced as a default hypothesis in the face of
>evidence of cross-K/T radiations of species (mammals and birds), rigid
>patterns of extinctions, and the apparently consistent pre-K/T decline  
>of non-avian dinosaurs?  
>
Rigid patterns?  Hardly.  Some groups had higher extinction *rates*, and a
few had 100% extinction, and a very few had no increase in extinction.  But
at the individual species level there is no discernable pattern.  Why did
one species of animal (say Alphadon marshi) survive and *close* relative
(say Alphadon wilsoni) die out?  (Note, both of these species are from the
Lancian fauna of North America, so not only were they close relatives, they
were sympatric - and this is not an isolated example).

Thus it is certainly true that larger sized species were more prone to
extinction, and species capable of extended aestivation seem to have been
particularly resistant to extinction.  But within each of these broad
categories, the fate of each individual species seems to be largely random
with respect to all known factors.

--------------
May the peace of God be with you.         sarima@ix.netcom.com