[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Dromomeron and Lagerpeton query
Having strange problems with Outlook Express, so here goes, using the clumsy
-------- Original-Nachricht --------
> Datum: Sun, 19 Jul 2009 05:06:43 -0500
> Von: David Peters <firstname.lastname@example.org>
> Betreff: Re: Dromomeron and Lagerpeton query
> Exactly my point. The pterosaurs are ALSO ingroup taxa and, as you
> suggest, the Nesbitt/Irmis studies are "getting random garbage as a
> result. "
Obviously, what you need to do to test this possibility is _add a new outgroup_
which, with enough certainty, lies outside the smallest clade formed by the
Plain as day, no?
> I followed Nesbitt/Irmis changing nothing but adding taxa in a TEST of
> their work.
That wasn't a test.
> > Remember: if you don't explicitly specify an outgroup, PAUP* uses
> > the first (topmost) OTU as the outgroup.
> > In this case, you'd either have to use *Huehuecuetzpalli* as the
> > outgroup or add a non-crown-diapsid outgroup to the matrix.
> Which means you have to KNOW something about the entire spectrum of
> amniote relations before embarking on making your taxon list. Not just
> follow the paradigm.
> The paradigm needs testing.
To root a cladogram by an outgroup, you need to assume that the ingroup is
monophyletic with respect to the outgroup. This assumption can only be tested
by an analysis with a bigger sampling, where both the ingroup and the outgroup
of the smaller analysis are part of the ingroup of the bigger analysis. To find
out if Nesbitt et al. screwed up by assuming the pterosaurs are part of their
ingroup, you need to conduct a bigger analysis, say with the crown of Diapsida
as the ingroup and the araeoscelidians as the outgroup, for example.
This, BTW, is why finding the root of the tree of life is so difficult and
proceeds using arguments from gene duplications and the like.