Re: Fastovsky vs Archibald

[Phil Bigelow <bigelowp@juno.com>]

On Sun, 26 Jun 2005 04:01:26 -0700 (PDT) Tim Donovan <uwrk2@yahoo.com>
writes:
> 
> 
> --- Phil Bigelow <bigelowp@juno.com writes:
>  
> > It is unwise to compare two different
> > paleoecosystems (e.g., the upland
> > Canadian formations  vs. the lowland Hell Creek
> > Formation) 
> 
>   The Scollard and Hell Creek do not look like
> different paleoecosystems. They had essentially the
> same dinosaur taxa despite a somewhat different
> environment, which may be significant.


Before we can claim that the Scollard and the Hell Creek are similar
paleoecosystems, we need to resolve a few issues.  Here are only a few
(of many):

The Scollard Fm. may have been deposited far from the WIS. Some workers
even claim that the Scollard, itself, had closed off the Seaway.  Others
claim that the WIS was open all the way to the Arctic even into the
Paleocene.  Take your pick.  But if the Seaway was closed off in southern
Canada by Scollard time, then the climate would have been harsher than it
was further to the south.

The Hell Creek Formation was deposited adjacent to the WIS, which
moderated its climate.

Is the flora assemblage in the Scollard Fm. identical to the flora
assemblage in the Hell Creek?  What about the diversity of
non-dinosaurian vertebrates? Are they the same for the two formations? 
How common are freshwater mollusks in the Scollard Fm.?  What percentage
of the Scollard is overbank mud?  Is that percentage identical to the
percentage in the Hell Creek Fm.?

Dinosaurs, alone, do not make a paleoecosystem.  Dinosaurs aren't even
considered to be candidates for being keystone taxa.  Just because the
Scollard Fm. and the Hell Creek Fm. had a roughly similar dinosaur
diversity doesn't mean that the two formations necessarily had identical
(or even similar) paleoecosystems.  One has to study the *entire* suite
of life in each formation.  And I argue, even down to the bacteria in the
paleosols, if it were feasable to do so.

 
> >or times (late
> > Maastrictian vs. Campanian), or both, and then draw
> > conclusions about
> > extinction based on that comparison.  


>   This is exactly what some of the leading authorities
> have been doing for many years e.g. Archibald, Clemens
> and Dodson.


Yes indeed.  And I don't think that approach is always wise.  These
workers distill things down to just species (or genera) vs. time.  Sure,
it's nice and tidy, and one can easily wrap one's mind around their
conclusions, but it may not convey any *informative* information.  In
contrast, I believe that a holistic paleoecological approach is needed
when interpreting the disappearance of taxa within a formation or between
formations..  And that means scouring a point in time at a point on the
earth and digging every piece of available information out of that
place/time.  A Gestalt approach to paleoecology is needed.  Dinosaurs are
only the tip of the Hell Creek iceberg, and their relative
paleoecological importance may be overrated.  And the Scollard Fm. can't
be used as a surrogate for studying the Hell Creek Fm. (and visa versa).

What were the keystone taxa in the Hell Creek Formation?  Are they the
same taxa in the Scollard Formation?  Were they pond scum, or worms, or
lice, or a more complex type of life?  And if we don't know what to look
at to answer that question, then perhaps we need to develop a whole new
paradigm for studying fossil life within sedimentary formations.


> See the latter's remarks in the extinction
> dialogue chapter of The Complete Dinosaur. Dodson may
> have erred when he wrote that nodosaurs and
> lambeosaurs were gone by Lancian time but it is still
> possible that they disappeared within Lancian time.


"Possible" and "proving it" are two different things.  Migration away
from the Hell Creek region or increased geographical restriction within
the Hell Creek region are two equally parsimonious interpretations of
that same data, and in theory they are both provable hypotheses.  But it
is nearly impossible to identify an undisputed extinction horizon within
a formation.  Absence of evidence is not necessarily evidence of absence.

All that we can say for certain is that, so far, no articulated nodosaur
or lambeosaur skeletons have been collected from the upper part of the
Hell Creek Formation.  We don't even have enough samples to correlate the
known nodosaur occurrences with depositional environments.  So, any
further elaboration or interpretation of the data is, at our current
state of understanding the paleoecosystem of the H.C.,  like putting
lipstick on a pig.  The lipstick might make the pig feel pretty, but the
pig is still just a pig.

<pb>
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