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Re: _Night Comes to the Cretaceous_




On Fri, 7 Aug 1998 Dinogeorge@aol.com wrote:

> 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?

No, but it makes it more probable that he will embrace an idea just
because it is Alvarez that is thinking it.  Someone a little less
comvinced of their own brilliance might expose any given idea to a little
more scrutiny.  And that's the problem with the bolide-as-sufficient-idea,
it does not withstand scrutiny (yet, anyway).

> ... 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.

But that's just it.  Measurement is difficult.  Taking Macleod et al 1997
The Cretaceous-Tertiary biotic transition. Journal of the geological
society, London, Vol154, 265-292  as gospel, the issue is still wide open.
This is true not only with vertebrates but with the entire biota.  Many
were going out in the Maastrichtian.  Often it was rare sp. that became
extinct.  Pseudo-extinctions (byproduct of adaptive radiations) are
confused with true extinctions.  On and on.  They conclude: "Results
suggest that many faunal and floral groups (ostracods, bryozoa, ammonite,
cephalopods, bivalves archosaurs) were in decline throughout the latest
Maastrichtian while others (diatoms, radiolaria, benthic foramnifera,
brachiopods, gastropods, fish, amphibians, lepidosaurs, terrestrial
plants) passed through the K/T event horizon with only minor taxanomic
richness and/or diversity changes."

With archosaurs, birds, depending on how you feel about the timing of
modern the splitting of modern orders, seemed to sailed through the K/T
just fine.  Non-avian data is pathetically lacking.  But at the very least
it is not possible to determine whether there was a sudden or a gradual
extinction.  Knowing all this, it is jumping to conclusions to claim
preeminence for a single cause. 

> 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.

You should be commended for looking beyond conventional explanations;
suggesting viable alternate theories about bird phylogeny.  I ask you
to consider that general acceptance of the bolide-as-sufficient idea is
a restriction to deeper thinking inasmuch as it sucks up research dollars
etc.  The point is the extinctions don't
"line up".  Even Alvarez and co. talk about "stepped extinctions".  It's
all in resolution.  From a distance it seems a single event.  But a closer
look reveals a more complex picture. I would have thought _this_
was common knowledge among those in the paleontological community.

> 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.
 
If "almost all" animals and plants were roasted I would agree with you.
But reality was much more complex.  And that tends to brand the
bolide-as-sufficient idea as trivial!