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




David Peters <davidpeters@att.net> wrote:


> 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)))). 


These are not sister groups to Pterosauria.  These taxa (_Erythrosuchus_, 
_Euparkeria_, Pseudosuchia/Crurotarsi) are successive outgroups to the 
Pterosauria+Dinosauromorpha clade (Ornithodira).


According to the analysis of Nesbitt et al. (2010), the sister taxon to 
Pterosauria is Dinosauromorpha.


> I , uh, fail to see the gradual accumulation of
> pterosaurian characters in this list. Perhaps you can help?


If you are referring to synapomorphies of Pterosauria, these characters would 
be gradually accumulated within the Pterosauria, after they branched off.  The 
characters that pterosaurs would have in common with _Erythrosuchus, 
_Euparkeria_ and Pseudosuchia/Crurotarsi would be plesiomorphic for 
Archosauriformes (or for less inclusive clades that include pterosaurs, such as 
Archosauria); or they are homoplastic.


> Which of these taxa, in your mind, is closest to pterosaurs?


Pseudosuchia/Crurotarsi is the closest outgroup; but this clade and Pterosauria 
are not sister taxa.  As I said, the analysis found Dinosauromorpha to be the 
sister taxon to Pterosauria.


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


You may be right.


> Fine. Keep them in. They don't contribute one iota to a better 
> understanding of the origin of dinosaurs, unfortunately. 


Then what's the harm in including them?  I would say that the fact that 
lagerpetids have been found (by many analyses) to be the most basal 
dinosauromorph clade suggests that they might be pivotal to our understanding 
of the origin of dinosaurs.


Cheers

Tim