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

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

>I was going to save my replies to this particular thread until it had
pretty
>much run its course, but this statement requires a short reply right away.
As
>has occurred all too frequently in the past, Jeff Martz once again
>misrepresents my position.

    I don't try to misrepresent your position George, but sometimes you kind
of contradict your own arguments depending on what you are arguing for.
This isn't meant as a personal attack, but you do it.

>"Don't just throw up your hands and say 'its too
>complicated to understand so it must be completely meaningless and
>incomprehensible' "?? Nonsense. How do you figure I think that? Isn't that
>what >computers< are for?


    I think that was a reply to Tracy, who seemed to me to be basically
making that point.

>First of all, I have detected an unspoken attitude among dino-cladists that
>"more is better": "Your analysis only has 258 characters? Hah. >My<
analysis
>has 356 characters. Therefore it must be better than yours." But how can
you
>compare either analysis against the other? There is simply no metric for
>doing this--certainly none that couldn't be challenged. So--we do a >third<
>analysis, perhaps with >even more< characters. And so on, ad infinitum.


    Having more characters in an analysis does not make it fundamentally
better.  However, if these characters seem to be generally true of the taxa
you are coding them for, are not due to distortion and reconstruction, are
not almost synonymous with another character you have coded, and show
variance between taxa, then more information is better.  Analyses can be
compared by not only comparing how much information is included for the
computer to make its decisions (how many characters there are) but by
judging how well thought out the characters are.

>Another problem is that there is no way to assess any one character against
>any other. How much is an overhanging zygapophysis worth versus an elongate
>prepubic process? As I understand it, most analyses weigh all characters
>equally and hope their numbers will distinguish the apomorphies from the
>homoplasies, but there is no a priori reason for doing the analysis this
way,


    Hold it; do YOU know how much an overhanging zygapophysis is worth vs.
an elongate prepubic process is worth?  Do you know if there is a
fundamental difference in value at all?  I don't know if less hair or a
bigger brain is more useful in distinguishing us from chimps, but we have
them both and chimps don't.  The only time it might be particulalry valuble
to but values on characters is if they are known to be particulalry
susceptible to homoplasy.
    Some analyses do play around with the characters they include in order
to see if they get something different, in a sense putting a relative value
on them.  I think this is a good tool.  Christopher Bennet's paper on
pterosaurs, in which he removed characters relating to locomotion to see
what the rest of the charatcers did to the placement of pterosaurs, is a
good example.  However, I think its probably always best to start off with a
analysis that includes ALL the characters and then experiment to compare
with that.  You then basically have a standard that lets you spot where the
contradictions are.

>Incidentally, in writing for the general public, such as in the new edition
>of the Bill Stout dinosaur book from Byron Preiss,

    Holy S*%&T!  When does this come out?!

>I'm gung-ho on cladistic
>analysis: best thing since sliced bread, etc., etc. My rants on this list
are
>meant to provoke thoughtful discussion among dinosaur aficionados. We
already
>know that cladistic analysis, full of holes though it is, is probably as
good
>as we'll see for a while in terms of obtaining phylogenetic information
from
>the fossil record. No sense giving the cr**t**n*sts any more ammo to
misuse.


    Oh....ok.  In that case never mind.  However, I think we are basically
making a concesion to the "C"s if we have to muffle our arguments out of
worry over them being misused or misinterpreted.

LNJ
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It is our duty to make the best of our misfortunes and not to suffer passion
to interfere withour interest and the public good.
-George Washington

It is your business when the wall next door catches fire.
-Horace
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Jeffrey W. Martz
Graduate student, Department of Geosciences, Texas Tech University
3002 4th St., Apt. C26
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