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Re: the evolution of disparity in body plans (was Re: synapomorphies)

Mickey wrote:

>Robert.J.Meyerson@uwrf.edu claims:
>> Since Gould's punk eq has shown quite convincingly that the tree of
>> life is actually shaped like a pine
>It wasn't punk eek, and it wasn't so convincing.  I'm presuming that
>Rob is referring to Gould's book _Wonderful Life_.  The book is great
>for its pictures, but most of the problematica described therein have
>since been placed comfortably into lineages with contemporary
>representatives.  In short, Gould's major thesis in that book was most
>likely wrong.

Well, one of SJG's theses is almost certainly wrong, but others are
correct. The 'replaying of events would produce different result' is right,
as is the fact that it would have been impossible for a Cambrian zoologist
to predict which groups would survive and which would become extinct.
However, his claim on maximum disparity is almost certainly wrong. The
arthropods we know and love/hate today are very derived forms based on
several distinct body plans. The Cambrian arthropods represent basal or
stem arthropods - arthropods when such clear divisions had not stablized.
Plus, back in the good old days of the Cambrian, there were new niches to
exploit and unsuspecting soft bodied organisms to eat, thus body design was
a tad more flexible. It is important to point out that while the Cambrian
arthropods look bizare to our modernocentric reference, our modern
arthropods would look equally bizare to a Cambrian zoologist.
"you mean _Anomalocaris_ didn't make it? Get out of here!"

I have the head of the ulna from _Iguanodon_ from the Isle of White. It is
heavy and black and reacts slowly with acid. Inside the cavity is filled
with coarse clear crystals (not calcite). Anyone know of Isle of White bone
preservation, or where I can read up on it?


cnedin@geology.adelaide.edu.au                  nedin@ediacara.org
Many say it was a mistake to come down from the trees, some say
the move out of the oceans was a bad idea. Me, I say the stiffening
of the notochord in the Cambrian was where it all went wrong,
it was all downhill from there.