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Re: Prolacertiformes and Protorosauria



Yes, there is some intuition that goes into judging results. 
ie. placing mesosaurs with pareiasaurs = bad.

More importantly, there is some experience at work here too. Yes, I've done the 
larger, more inclusive study, that indicates the breaks are real and taxon 
exclusion is the culprit.

As for your 'by definition' comment, yes. True. Even so, 'by default' is also 
at work here. The authors were working from too large a gamut and too small of 
an inclusion group to make sense. There are better sister taxa out there. The 
larger study would have revealed this.

David Peters
davidpeters@att.net


--- On Sat, 5/16/09, Mike Habib <habib@jhmi.edu> wrote:

> From: Mike Habib <habib@jhmi.edu>
> Subject: Re: Prolacertiformes and Protorosauria
> To: davidpeters@att.net
> Cc: "dinosaur mailing list" <dinosaur@usc.edu>
> Date: Saturday, May 16, 2009, 10:44 AM
> David Peters wrote:
> 
> > Once again, if sister taxa don't bear a family
> resemblance, you have to doubt the results.
> 
> Wait - I'm confused: don't the sister taxa bear
> "family resemblance" *by definition*?  The tree
> constructs the best estimate of ancestry, using some kind of
> estimate of family resemblance.  For morphological character
> sets, this usually means using a parsimony algorithm, with
> is optimizing the distribution of characters and using
> synapomorphies to define clades.  Since you're joining
> taxa using shared derived character states, they *must* bear
> resemblance.  The fact that those taxa may have some kind of
> qualitative or intuitive lack of "resemblance"
> doesn't mean you screwed up.
> 
> 
> > I added breaks at nodes that did either had closer
> excluded sisters or just plain did not make sense. Without
> an overall understanding of amniote relations, studies such
> as this one, undertaking such a huge gamut with too few real
> sisters will bear little real results.
> 
> How do you determine which groupings make sense - isn't
> that the point of constructing the tree in the first place? 
> What's a "real sister"?
> 
> Cheers,
> 
> --Mike
> 
> 
> 
> Michael Habib, M.S.
> PhD. Candidate
> Center for Functional Anatomy and Evolution
> Johns Hopkins School of Medicine
> 1830 E. Monument Street
> Baltimore, MD 21205
> (443) 280-0181
> habib@jhmi.edu