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re: Pleistocene & K/T extinctions



To John Alroy, et al.

     Responses to posting Friday:  I've been in the field.

   ""Europe. I don't know the dates off the top of my head, but I
seem
to recall the Eurasian extinctions are substantially earlier than
those in North America but occur when Homo sapiens is going
through
its big migration/population increase phase on that continent.""

--Not so. Mammut cuviensis(?), Mammuthus primigenius and numerous
other
proboscidean species, cave bears, rhinos, cave lions, several
horse species,
woolly rhinos, and a few other large taxa all dissappear at the
end of what we
call Rancholabrean time in US, which is ca. 9500-10,000 ka. As I
note below,
there is absolutely no equivalent invasion in Europe to
correspond with the
Asiatic immigration across Beringia.


   ""The Australasian extinctions are another case of extinctions
well before
the North American extinctions, certainly much earlier than 10
kybp.
The African extinctions are earlier still.""

--What are we discussing here? Which Australasian exitnctions?
Those of the past
few centuries by European-descendants?  Which African
extinctions? They still
have a significant megafauna.


    ""...I find it implausible that the same "climate" factors
are responsible
for the SELECTIVE extinction of completely unrelated mammals in
Australasia and
the rest of the world (marsupials vs. placentals).""

--Huh? What, again, is the subject? The selection for marsupials
in Australia
occurred well before the appearance of humans! I believe it was
sometime back in
the Paleocene.


     ""no directed human invasion" in Europe? Technically
speaking this
may be right if Homo erectus is "human" or (here's a new one) if
H.
erectus not only was directly ancestral to H. sapiens, but gave
rise
to the latter through an agonizingly (shall we say "glacially"?)
gradualistic process. Then maybe we could say there was no human
"invasion" of Europe in the late Pleistocene.""

--We're going off to deep space again.  The point of discussion
was whether or
not paleoindians caused the N.A. megafaunal extinction event of
ca. 10ka. right?
If so, the above is irreelevant.  I noted that there was a
parallel megafaunal
extinction in Eurpoe at the same (10ka) time without a notable
concurrent invasion of humans.  You are not addressing the topic.
That humans
may kill off animals is obvious.  Whether there are alternative
views to
the specific event, and your suggestion that anyone who holds
such views is
oblivious, is the point.


    ""But I doubt we're going to find many paleoanthropologists
at this point who
really think H. erectus was the direct ancestor of H. sapiens;
that H. sapiens
was present in Europe much before 40 - 50 kybp; or that the
appearance of H.
sapiens (whatever caused it) was gradual....""

---Here again you are demonstrating considerable sophomorism and
a somewhat
disturbing sense of intolerance for alternate ideas. First, there
are many
solid, professional paleoanthropologists with exactly the view
you believe is
invalid;  e.g.  Wolpoff at U. Michigan. There is some current
literature making
precisely this point. Also, you are appareently unaware that
"Neandertals" are
H. sapiens and that the record in Europe is now traceable to over
300,000 yrs.
Also, some new material from England and Spain shows that
anatomically modern H.
sapiens may have been contemporary with the "Neandertals" in
Europe and Africa.
I believe you're really out of your field here.


      ""I'm sorry, but at this point it sure looks to me like
"gradualists
are practicing an obsolete science" (not my phrase, but it will
do).
Standard genetic models (in evolutionary debates) and standard
geophysical processes (in geological debates) all predict large
variation in rates of change. Therefore, it's actually strict
gradualism and not punctuationalism that requires extraordinary
processes......""

 --Its nice that you have learned from your mentors so well, but
the world of
paleontology is not black and white.  Most of us are neither
"gradualists"
nor "punctuationists."  The record is what it is, the
interpretations vary. I
have observed several gradually evolving lineages in my work,
such as Exogryrine
oysters, species of the giant teleost Xiphactinus, subspecies of
sevreral sharks
(e.g. Squalicorax kaupi and pristodontus) in the Late Cretaceous,
and  species
of the Ehmaniella-clade among Cambrian trilobites.  I have also
noted many
lineages of apparently rapidly changing and static taxa.

    Let me guess: how many hands-on, species-level taxonomic
studies did you do
in your brief career to date?  Aren't your really passing on the
gospel according
to Raup and Sepkoski?  Its nice to be loyal, but as a new
graduate, try thinking
for yourself and observing the world for a while.


      ""U of C. Yes, I'm a recent graduate of the U of Chicago
(actually,
I just defended and I graduate in August). Does that make me some
kind of a leper?""

    No, just sophomoric.


    ""great deal of valid counterpoint to the impact hypothesis"?
This
may have rung true circa 1981 or even 1991, but at this point I
think
the anti-impact people are fooling themselves. It's perfectly
reasonable that a lot of people in the scientific community who
aren't in the thick of things might think there is a reasonable
debate still going on. It's perfectly insane that certain people
could continue to oppose the impact model after attending
symposium
after symposium where they are confronted directly with the
evidence.
I'm sorry, but I've SEEN the anti-impact people in action at a
symposium during the last GSA meeting.""


    Maybe you saw some fools in action.  But there's a large body
of refereed
literature out there counterarguing your heartfelt beliefs.  I
don't have your
childlike faith in the impact scenario. I believe I'm not a fool.


     ""Stress below the K-T. I think everyone agrees that the
world was a
very interesting place in the late Maastrichtian...the
reef-building rudist
bivalves seem to have gone out well before the boundary, and so
on...."

   There' a lot more than rudists in that "so on", including
ichthyosaurs,
elasmosaurids, many dinosaur taxa, galeomorph shark taxa,
numerous heteromorphic
ammonoids, many taxa of "holostean" fishes, etc.  Most
significantly, the overall
appearance of the fauna changes, a [phenomenon observable in the
field by
proportions of taxa represented, but easily masked in data
tabulations.


     ""Dr. Schwimmer's earlier papers are largely on Campanian
fossils, so perhaps the data he mentions are still in
preparation.""

    You're correct, my work has been mostly Santonian-Campanian
vertebrates. But
the K/T data are observations from visiting and collecting
boundary sections in
Alabama, west Texas, New Jersey, Montana, and Wyoming. I publish
largely
taxonomic and biostratigraphic works because I believe these make
a
significant contribution.  "Extinction models" in my experience
have short
scientific shelf-lives.  Tell us, how many K/T boundary sections
have you
personally studied?
   Parenthetically, I have a Late Cretaceous marine
biostratigraphic study in
progress, covering the Gulf and Atlantic Coastal Plains.  It will
include the
entire Cenomanian to Maastrichtian vertebrate fauna. I'll be glad
to send drafts
when the work is done.


  --""Scientific Method." I'm amazed to find myself being accused
of
having no familiarity with the "Scientific Method.....""

  Here I probably was hasty, and I apologize.  I meant to say
that objectivity
is the critical element of the Scientific Method, and I found
your comments
quite close-minded.  This is especially irksome because you
indicate that you are
entrusted to review manuscripts for Paleobiology: I make a
special effort to be
neutral when I review a paper by a colleague who's opinions I
differ from: I hope
you do too.

David Schwimmer
Columbus, GA
schwimm@uscn.cc.uga.edu