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Re: paleontolgist, dinosaur and also Re: "Wonderful Life" - , repeated.



From: John Bois <jbois@umd5.umd.edu>
 > On Thu, 14 Nov 1996, Mickey P. Rowe wrote:
 > >  The
 > > extinction pattern was not specifically targeted at the dinosaurs.
 >
 > If you want to call Archibald's data into question, fine.

We must be looking at a different data set :-)

What I saw in Archibald's data was a wide range of extinction levels,
from 0% to 100%.  And, except for an excess of untouched taxa, the
distribution I see is very close to uniform (though it is hard to
tell for sure with such a small number of taxa).

So, in taxa that were involved in the extinction, the level of impact
seems to have been more or less randomly distributed. This is really
pretty much "not specifically targeted to dinosaurs".

Now, yes, there are ecological correlates to the differences in
extinction levels, with most of the 0% and near-0% taxa restricted
to a relatively few ecological guilds. And all of the taxa with more
about 25% extinction had few, if any, species in these favored guilds.
So, yes, in this sense the extinction pattern was non-random. And note,
dinosaurs had, as far as I know, NO species in any of the favored
guilds.  This, in combination with a wide stochastic variation in
impact, may well be sufficient to texplain the 100% extinction in
dinos, without any need for any specific targeting of dinosaurs.

 >  If you won't
 > allow the discussion to relate to terrestrial only, fine.

Why should the discussionb be restricted to the terrestrial extinctions?
Given that the marine and terestrial extinction apparently happened at
the same time, it is much simpler, in the absence of evidence to the
contrary, to assume the same or related causes were involved in both
sets of extinctions.  Thus, unless there is reason to believe that the
marine extinctions were independent of the terrestrial ones, then I
will be skeptical of any mechanism that does not also help explain the
marine extinctions.

 >... only marsupials and lizards suffered greater than 50%
 > extinction rates (roughly 90% and 75% respectively).  And these are
 > expected because of replacement and predation by the burgeoning
 > placentals.

Not to me, they aren't.  Both groups retained high diversity right
up until the very latest known Lancian samples, and are at a very
low diversity in the earliest post-Lancian fauna samples. Also, the
burgeoning of the placentals cannot really be demonstrated until
*after* the extinctions were over. (All of ?Clemens's? supposed
intermediate faunas appear to be admixtures, due to stream-bank
erosion).

This puts those extinction right in there with all of the others,
as part and parcel of the terminal Cretaceous event.

 > caricaturing the pattern.  Remember the original challenge to Stan
 > Friesen was to match the events with the known data.  It's hard to do
 > because their _is_ a pattern in the extinctions.
 >
Yep, there is a pattern - an ecological one, not a taxonomic one.

And each of the factors I propose as contributing help explain *part*
of that pattern, according to Archibald's own "expectation" grids.

swf@elsegundoca.ncr.com         sarima@ix.netcom.com

The peace of God be with you.