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

[Mike Habib <habib@jhmi.edu>]

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