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Re: justification for excluding lagerpetids and/or pterosaurs from a phylogenetic analysis of the Archosauria




On Mar 5, 2010, at 10:23 AM, David Peters wrote:

Tim W. wrote:

In this instance, I think the problem(s) might be yours alone. I cannot see
any justification for excluding lagerpetids and/or pterosaurs from a
phylogenetic analysis of the Archosauria.


Perhaps not quite alone:

From the JVP abstracts of 2008: A SUPERTREE APPROACH TO PROLACERTIFORM PHYLOGENY by SOBRAL, Gabriela, USP, Ribeirao Preto, Brazil; LANGER, Max, USP, Ribeirao Preto, Brazil "the majority consensus tree shows a paraphyletic Prolacertiformes with two major clades: the “Avicephala” clade includes, among others, drepanosaurids, Longisquama, Sharovipteryx, and Pterosauria."

Echoing Tim: I fail to see how this justifies the exclusion of lagerpetids and/or pterosaurs from a phylogenetic analysis of Archosauria. The fact that some authors find pterosaurs to fall outside of Archosauria does not mean that pterosaurs should be excluded from archosaurian analyses, any more than the papers finding pterosaurs to fall within archosaurs indicate that you should exclude them from your lepidosaurian tree. Pterosaurs might not be archosaurs - that does not mean that they cannot be included in an analysis looking at Archosaurian relationships. If I produced a tree tomorrow that found snakes outside of lepidosauria, then is every subsequent worker suddenly obligated to exclude snakes from every future lepidosaurian analysis?


Tim W. wrote (again):

In this instance, I think the problem(s) might be yours alone. I cannot see
any justification for excluding lagerpetids and/or pterosaurs from a
phylogenetic analysis of the Archosauria.

Lucky for us, Nesbitt et al. 2010 provided all the justification anyone would need as they listed several (in their study) sister taxa for pterosaurs: Erythrosuchus + (Euparkeria + (Revueltosaurus + Aetosaurus) + ((Arizonasaurus + Effigia) + (Batrachotomus + (Postosuchus + Dromicosuchus)))).

I , uh, fail to see the gradual accumulation of pterosaurian characters in this list. Perhaps you can help? Which of these taxa, in your mind, is closest to pterosaurs?

I fail to see what it matters whether or not we can intuitively see the gradual accumulation of characters on the tree. Cladistic methods optimize characters in a step-wise addition/reversal series *by definition*, so there is a gradual accumulation of characters on *every* tree built with cladistic methodology. Now, it may not be a simple accumulation - some trees might have add characters evenly across branches, while others may have a more uneven distribution of recovered synapomorphies. Some trees may imply many reversals and convergences, while others may imply few reversals (the latter being a more classic case of character "accumulation") - none of these contrasts speak to the validity or accuracy of a tree.

Taxon inclusion/exclusion is still the big kahuna. Pterosaurs don't belong in this neighborhood.

We don't know which neighborhood they belong in yet. Arguing for taxon inclusion is reasonable - your argument for taxon exclusion is weak.

Cheers,

--Mike


Michael Habib
Assistant Professor of Biology
Chatham University
Woodland Road, Pittsburgh PA  15232
Buhl Hall, Room 226A
mhabib@chatham.edu
(443) 280-0181