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RE: Pterosaurs as basal archosauriforms



The problem with this is that even if we found Nesbitt (2011) also had hindlimb 
characters incongruent with other regions when it comes to placing pterosaurs, 
Bennett's methodology for combining and defining characters leads to composites 
that can't be coded correctly.  You could say Nesbitt's avemetatarsalian 
characters "(1) Distal end of neural spines of the cervical vertebrae 
unexpanded (191-0)" and "(2) Distal expansion neural spines of the dorsal 
vertebrae absent (197-0)" should be combined as both involve presacral spine 
tables, but what to do about Herrerasaurus that has expanded dorsal spines but 
not cervical spines?  Or that "(3) Second phalanx (5 2.2) of manual digit II 
longer than first phalanx (255-1)" and "(4) Trenchant unguals on manual digits 
I–III (257-1)" are both predatory manus characters, but Plateosaurus has 
trenchant unguals yet short penultimate phalanges.  Bennett wrongly thought 
this kind of variation didn't exist (or could be ignored?).  Or you could 
define a new predatory manus character by saying dinosaurs have trenchant 
claws, elongate penultimate phalanges, short fourth fingers and no pteroid, 
while pterosaurs have trenchant claws, elongate penultimate phalanges, long 
fourth fingers and pteroids.  And that these should be unordered states along 
with a "predatory manus absent" state.  But you'd just be artificially making 
pterosaurs seem dissimilar.  So of course by eliminating most of the 
avemetatarsalian characters, pterosaurs will likely go somewhere else.  We know 
that when simiosaurs, Longisquama, Cosesaurus, Sharovipteryx and a 
tanystropheid are added to Nesbitt's matrix, moving Pterosauria outside 
Archosauriformes gets easier- down to only 13 more steps.  And Nesbitt only has 
11 unambiguous avemetatarsalian apomorphies.  So adding in a few other 
characters that support non-archosaurian pterosaurs could tip the scales.  But 
what would it prove besides that artificially eliminating support for a certain 
clade leads to that clade not being supported in the most parsimonio!
us trees?
 most arctometatarsalian characters of alvarezsaurids- they ended up as 
maniraptorans.  Or Sereno's analysis that left out most support for 
Maniraptoriformes- tyrannosaurids ended up as maniraptorans.

To actually test Peters' idea, we'd need an analysis covering all of Sauria at 
least, with characters meant to resolve deep splits as well.  Redescriptions of 
Longisquama, Sharovipteryx and Cosesaurus wouldn't hurt either.

Mickey Mortimer

----------------------------------------
> Date: Wed, 26 Sep 2012 00:13:51 -0300
> From: augustoharo@gmail.com
> To: mickey_mortimer111@msn.com
> CC: dinosaur@usc.edu
> Subject: Re: Pterosaurs as basal archosauriforms
>
> > Bennett uses an outdated analysis, unfairly eliminates most characters
> > supporting avemetatarsalian pterosaurs, doesn't include the best
> > candidates for non-archosaurian pterosaurs, and espouses a horrible,
> > subjective cladistic philosophy.
>
> The methodology of this study should be applied to Nesbitt's (2011)
> large study of archosaur phylogeny, with the addition of some few
> non-archosauriform archosauromorphs, to test whether or not the same
> pattern emerges.
> Cheers,
> Augusto.