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Re: Cladistic question (was synapomorphies)

>I'm not exactly clear, but surely there are other criteria on what animals=
> to include in a cladistic analysis.  I mean, one wouldn't try to build a=
> cladigram that included _Camptosaurus_ and _Dienonychus_, since the two are=
> clearly different from each other.  How do cladists decide what animals to=
> include in their studies?  And wouldn't this add an element of opinion into=
> the results, since the researcher would have to decide what animals to=
> include in the study?

I really do not understand the first statement that one wouldn't want to "build"
a cladogram for Camptosaurus and Deinonychus.  Why not, if you are interested in
how these animals are related to each other.  Just because you can distinguish
them tells you very little about how they are related.  In reference to your
question about how cladists decide which animals to include in their
analyses, we
pick what is appropriate.  For instance in my work on early equids, my
analyses include early equids, paleotheres, tapiromorphs (tapir and rhino
ancestors), hyracoids
proboscideans, phenacolophids, Radinskya, and phenacodonts.  The idea is
that I have
all of the appropriate organisms that might or might not be closely related
to the group I am interested in, and thus my analysis is likely to be more
robust than if I just looked at the equids.  If this means that there is
some subjectivity to my analysis, so what?  all analyses are going to be
somewhat subjective, all cladistics tries to do is make the assumptions and
inferences as explicit as possible.
David J. Froehlich                              Phone: 512-471-6088   
Vertebrate Paleontology Laboratory                Fax: 512-471-5973
J.J. Pickle Research Campus
The University of Texas, Austin, Texas 78712