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



On Tue, 13 Feb 1996, Chris Nedin wrote:

> 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.

I see the "Ur-arthropod" as a many-segmented, untagmosed animal with 
unspecialized, biramous limbs.  Does anyone have a problem with this 
interpretation?  I see the Cambrian arthropods as a carpet of independent 
specializations from that primitive state, of which only four survived 
the Cambrian:  trilobites, chelicerates, crustaceans, and members of the 
myriapod-insect line.

> "you mean _Anomalocaris_ didn't make it? Get out of here!"

I have a hard time believing that _Anomalocaris_ belongs to a modern 
phylum.  Or _Obapinia_.  Or _Odontogriphus_, _Wiwaxia_ (I am unconvinced 
by the sea mouse comparison), _Amiskwia_, or _Nectocaris_ (my personal 
fave), for that matter.  To what phyla do these supposedly belong?

> Chris
> 
Nick Pharris
Pacific Lutheran University
Tacoma, WA 98447
(206)535-8204
PharriNJ@PLU.edu

"If you can't convince them, confuse them." -- Harry S Truman