Re: The validity of cladograms (was Re: giant birds)

[chris brochu <cbrochu@fmppr.fmnh.org>]

Martin Barnett wrote:
> 
> I am interested by this notion of cladograms being untestable as it looks to
> me like we have a control test with extant organisms.  Ie, get a bunch of
> skeletal experts to draw up a cladogram as they would with fossils, but
> based on living animals.  Then get a dna comparison of all the species
> involved and compare the more reliable dna test with those of the cladogram
> to see if they compare.  Has this or anything like it been done?  BTW, I'm
> assuming the dna test is more reliable than cladistics, otherwise:
> 
> Barrister:    Can you prove that this man is the father of your child?
> Plaintiff:      Yes sir, I got a palaeobiologist to look at their bones and
> it's conclusive...


This is done quite frequently, but there's currently a lot of work being
done on the general issue of "taxon sampling" - i.e. asking whether the
inclusion of certain taxa will actually change the outcome of the
analysis.  The kind of test you propose steps right into that question.

A classic paper on the subject is Gauthier et al's 1988 consideration of
"Haemothermia," in which they showed that matrices including only living
amniotes support a different (and arguably less tenable) tree than do
matrices including fossils.

Also - on what basis do you regard DNA tests as "more reliable?"  


chris





> 
> Yours sincerely,
>                           Samuel Barnett
> 
> > Since we have found ourselves debating cladistics again, and hearing the
> question of how valid it is, here's an idea for an interesting experiment:
> >
> > Let's say that a researcher is attempting to build a cladigram for the
> dromaeosaurs.  That person goes through the rigors of a cladistic analysis.
> Now, lets say that, by some horrible bookeeping error, one finds that the
> data for a sauropod and (HORRORS) a ceratopian has been included with the
> data for dromaeosaurs.  Now, according to cladistic theory, the resulting
> cladigram should look something like this:
> >
> >         DM        SP     CT
> >         \         /      /
> >          \       /      /
> >           \     /      /
> >            \   /      /
> >              V       /
> >               \     /
> >                \   /
> >                 \ /
> >                  V
> >
> > Where CT = Ceratopian; SP = Sauropod; DM = Dromaeosaur Mess
> >
> > The question I have is: Has this been done?  Will we get the result above
> or something else?  If we get a cladigram that includes CT *within* DM, we
> could be in trouble.
> >
> > Along these lines, since the researcher is the one who decides what
> characters are used in a cladistic analysis, does this make the cladigram
> subective?
> >
> >
> > Rob Meyerson
> >
> > ***
> > Politicians and diapers have one thing in common. They should both be
> changed regularly and for the same reason.
> >
> >
> >
> >

-- 
----------------------
Christopher A. Brochu
Department of Geology
Field Museum of Natural History
Roosevelt Road at Lake Shore Drive
Chicago, IL 60605

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