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Re: Re: propaganda of the majority
>No doubt about it, there is _more_ evidence for a dinosauria->aves
>relationship than crocodilia->aves. However, it should be noted
>that alot of this case that's been built for the dinosauria->aves
>connection is based on the foundation of cladistic analysis. I don't
>think I'd ever be convinced by cladistics data alone for 2 reasons:
>- There's way too much subjectivity in choosing characters for
> cladistic analysis.
Choosing cladistic characters is no more subjective than choosing characters
for any other study: in fact, its what is done with those characters that
is the only substantive difference between cladistics & traditional
systematics (cladistic taxonomy is another kettle of non-tetrapodan
>- No standard methodology exists for differentiating between similarities
> inherited from a common ancestor and similarities due to convergence.
Actually, here is where cladistics (as it should be done) differs from
previous methods. Done correctly, there should be no a priori decision over
the synapomorphoic vs homoplastic (convergent) nature of the characters -
code all of them in and see how they fall out in the most parsimonious
tree(s). This is the method I use in my new theropod phylogeny, and my
biggest beef with Gauthier's '86 paper (he chose a priori to keep some
characters out since he considered them "convergent"). Convergence can only
be determined a posteriori.
>>Luis Chiappe has already run the test that should be done (i.e., include
>>both crocodylomorphs, dinosaurs, primitive birds, and advanced birds) in the
>>same analysis. His results supported the theropod origin.
>I have not yet seen Chiappe's study, but I'd like to add a few more
>general comments about cladistics analysis shortcomings.
>If you have ten cladists do an analysis on a data set, you will get up to
>ten different results.
Not entirely true. If you give ten cladists the same matrix, they will find
the same cladogram. It is in people's selecting particular characters vs
other particular characters that produces the difference. My personal
philosphy (as expressed above) is to screw high confidence values and put in
as many characters as you want.
Additionally, any ten traditional systematicists produced up to ten
different phylogenies in the "good old days", so cladistics is no worse
than traditional systematics in this regard. Cladism does offer some
testable hypotheses that are lacking in less explicit systematic
> At best, you know only one of them can be right.
>This illustrates why Martin et al become upset by the rather dogmatic
>statements that have been made over the past several years (Padian and
>Gauthier, etc.) which imply that because you've done a cladistics analysis
>you've somehow arrived at the truth.
This concerns (perhaps not unwarrented) ad hominem arguements: just because
you don't agree with the way in which another worker acts about his work
does not mean that that work is wrong. Phylogenetic systematics has
historically suffered from some rather insufferable characters, but that
doesn't mean that the methodology is inferior to those practiced by more
polite individuals. A cladistic analysis does not necessarily mean it is
the truth, but does produce a single set of most parsimonious answers which
can be tested in the future by several following methods:
addition of new taxa
addition of new characters
correction of previously entered characters.
Thus, there is a single group of "right answers" (most parsimonious
cladograms) to any cladistic data matrix. It is the matrix itself that must
be tested in the future.
>We had some discussion on this about a month ago. John Ostrom is a hero
>of mine, but I do pick a bone with his cursorial origin of flight theory.
>I could repost all of my questions/problems regarding the theropod-bird
>hypothesis if you missed it.
You don't have to post them (I do know that some people get offended when
the same postings appear every couple of months), but you could send them to
me directly. I just started up on this list less than a month ago, so
obviously I didn't see them.