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Re: Dromomeron and Lagerpeton query

On Jul 19, 2009, at 8:39 AM, David Marjanovic wrote:

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.

Agreeeed! The bigger inclusion group is needed.

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 is assuming the traditional "crown group Diapsida" is monophyletic, which has never been tested. And so we really do have to test the entire Amniota. Until that's done, we're looking for our keys without the nightlight.


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.