Cladistic question (was synapomorphies)

[Robert.J.Meyerson@uwrf.edu (Rob Meyerson)]

David J. Froehlich writes;

>(I will use an example that has been used to
>death,
>ie bird/bat/pterosaur wings) we can hypothesize that wings are a shared
>derived feature for birds, bats and pterosaurs.  When we run the analysis (=
with
>enough information) we will end up with a topology that does not unite thes=
e
>three taxa.  Thus this is homoplasy not synapomorphy (but we could never
>have known
>this without the cladogram).

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?

Rob

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"Don't Panic."
        -HGTTG