>From:    G Thomas Watters <[log in to unmask]>
>Subject: Re: Classification and Southern Synthesis
>
>Damn cladists! There's more to it than a single gene for God's sake! When
>they've looked at all the genes, get back to me.

I agree to a point.  We have to look at more than one gene, but it least it
is a start.  A jumping off point if you will (insert your own joke here).
The problem with "conventional" classifications posed in the past is that
there are no testable hypotheses of the supposed higher relationships.  It
is all based upon opinion.  I do agree that more genes need to be looked
at, ALONG with additional morphological data, and a consensus tree
generated.  There is still a long way to go in identifing and coding
morphological characters as well.  The resulting tree from the COI data is
interesting though and it doesn't completely upset some of the older
hypotheses of relationships (i.e. the Mycetopodids and Mutelids being
sister groups; the Australian and SA hyriids form a clade as well).  The
most perplexing thing was that Coelatura fell outside of the clade with
Unionidae and Margaritiferidae, making Unionidae paraphyletic (unless you
include the margaritiferids in the Unionidae in which case the family is
monophyletic again).

> The trigonaceans may not even be ancestral to the unionaceans, despite
>"conventional wisdom." The
>Pachycardiids are probably the most closely related group, but they are all
>extinct. The study you mentioned found Neotrigonia to be the most similar
>among the groups used, but then they could only use living animals -
>pachycardiids would never even enter into their database. It would be like
>a DNA study of Nautiloids -- of course they would find the Coleoids the
>closest because they have no Ammonoids to compare. It's a shoe-horn
>approach to pop taxonomy. Damn cladists!

Actually Neotrigonia was only used as an outgroup to code the characters
for the Unionoids and as you say you can't use an extinct taxon for genetic
studies.  The idea is to choose a taxon that is as close to the ingroup as
you can without having it actually be in the ingroup.  That is not to say
that Neotrigonia is the sister to all other unionoids as that wasn't the
objective of the study.  It would be interesting to test a morphological
dataset of higher relationships in Bivalvia and see where the pachycardids
fall out with respect to unionoids, etc.

Kevin
Kevin S. Cummings
Research Scientist
Illinois Natural History Survey
607 E. Peabody Drive
Champaign, IL 61820
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http://www.inhs.uiuc.edu/cbd/collections/mollusk.html