Re: Gaia theropod follow-up: a "new" phylogeny

["Jeffrey Martz" <jeffmartz@earthlink.net>]

I said...

> < However, if you mean that cladists should limit the number of valid
>features which do seem to show significant similarities and differences
>between taxa, I find this a hard position to defend...
>Go through Holtz's or anyone else's data matrix and decide which characters
>have significance in determining evolutionary relationships and which don't
>before you decide which are "noise".

philidor11@snet.net said...
>On what basis would you 'decide which characters have significance in
>determining evolutionary relationships and which don't...'?
>You're making the assumption that we know the clues from the red herrings
>already (as well as the logic needed to assemble these clues).

     It isn't just assumed.  There are particular reasons why we think it.
A great example is tooth counts.  If we are counting the number of, say
maxillary teeth, in many reptiles (including mosasaurs which I have worked
on, and aetosaurs which I am working on now), they can be highly subject to
individual variation.  You might have nine maxillary teeth in one individual
and ten or eleven in others; you might even have different tooth counts on
both sides in a single animal!  Tooth counts might also vary with ontogeny.
If you are running an analysis on a bunch of closely related species that
have serious overlap in the variability of thier maxillary tooth counts,
tooth count data is hard to squeeze anything useful out of as far as
determining how they are related.
    Of course, this is based on what we know NOW.  Before, perhaps I should
of said good characters are "USEFUL in determining evolutionary relation
ships based on our CURRENT understanding of them".  To take a ridiculously
unlikely extreme example, we might find a huge bone bed that shows us that
one tooth count in particular predominates above all others, and that this
is the tooth count seen in most juveniles of that taxon, and then find
another such bone bed at a lower stratagraphic level with perhaps slightly
more primitive members of that taxon where ALL preserve that tooth count.
Then we might infer that this is actually the plesiomorphic count for that
taxon.
    Of course, we would then have to run a new analysis with this pesky new
information, because we were too stupid to use our psychic powers to predict
that this new information would come up and carelessly ran an analysis
without using tooth count data.  Sloppy sloppy.

>If we do know the clues, then isn't there an implicit assumption that
>universally applicable rules of evolution are known?

    I don't know about "universally applicible rules of evolution", but you
might notice something which seems to have application for the particular
group you are working on.  Like George, you seem dead set on finding
universal laws for perfectly generalizing everything.  Evolution (like
sedimentary geology) is a little too complicated for that.

>After all, the
>important situations can be identified and the intervening steps on the way
>to those situations determined.
>If this is true, then there is very little randomness in such a structured
>hypothesis.  You should be able to postulate an  initial situation and
>process leading to any given (identified) significant outcome.

>Instead of just comparisons to past charts, wouldn't it be appropriate to
>lay out the implicit scenario, including whether the process was adaptation
>or some other mechanism?

    Maxillary tooth counts show individual variation.  I don't know WHY that
is, only that it has been observed, and at least in some cases seems to be
too variable within taxa to provide information about the relationships
between taxa.  Moreover, cladistic analysis is looking for patterns in
character variability, it doesn't care if the the changing character is
adaptive or not.  After the analysis is run, we can speculate on what it
might mean, and perhaps play around with them in furture analyses to see
what we get.

>This just seems an ambitious assertion.  I'd appreciate a bit more
>persuasion.


    I do hope this elucidating explanation of my ambitious assertion has
persuaded your dubious skepticism.

LNJ
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Jeffrey W. Martz
Graduate student, Department of Geosciences, Texas Tech University
3002 4th St., Apt. C26
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