Re: Sobral and Langer 2008 (was pteros have lift-off)

[dinoboygraphics@aol.com]

Tim Williams wrote:

> > > However, I can only re-iterate David M.'s message that supertrees do
not contain any new data.  They pool together pre-existing trees.<<<

(sorry, in my haste to clear my in-box yesterday I had already 
deleleted David's email, which I'm sort of paraphrasing from here)

I'm not sure I agree with the definitions of "data" and "testing" 
implicit in the statement(s) that a supertree has/does niether.  I'm 
sure most phylogenetic workers have rerun published trees to check and 
make sure the original authors did it correctly, and by any working 
definition I use checking results would be "testing" a dataset.  
Moreover, if you achieved a different result, by any useful definition 
that new result would be new data, even though the input dataset was 
itself (presumably) not new.  Of course if you were the one in error it 
may turn out to be useless data, but that doesn't change the fact that 
new results from running the "same" data is very much itself data.

To be sure, a supertree may not be terribly convincing by itself (and 
all of the other problems with possible result bias mentioned by David 
and Tim are real) but we shouldn't dismiss the results of a 
meta-analysis a priori on methodological grounds, we need to look at 
the matrix and see where bias (e.g. resulting from mixing 
incongruous/largely non-overlapping data matrices) exists.

Note this isn't for or against any of the phylogenetic hypotheses being 
bandied about for pterosaurs, just a quick observation on methodology.



Scott Hartman
Science Director
Wyoming Dinosaur Center
110 Carter Ranch Rd.
Thermopolis, WY 82443
(800) 455-3466 ext. 230
Cell: (307) 921-8333

www.skeletaldrawing.com

-----Original Message-----
From: Tim Williams <tijawi@yahoo.com>
To: dinosaur@usc.edu
Cc: davidpeters@att.net; tijawi@yahoo.com
Sent: Thu, 22 Jan 2009 5:40 pm
Subject: Re: Sobral and Langer 2008 (was pteros have lift-off)






David Peters wrote:


> Sobral, G. and Langer, M. 2008 JVP 28: supplement to (3):
> 145A A supertree approach to prolacertiform phylogeny


Thanks.  However, I can only re-iterate David M.'s message that 
supertrees do
not contain any new data.  They pool together pre-existing trees.


> No taxon appears suddenly in the fossil record!


Sure they do.  It happens all the time.  How many basal bats 
(chiropterans) do
we know of, for example?


> There are always clues to ancestry.


I agree.  But in the absence of basal forms, these clues often arise 
indirectly
- such as by examining the character states that derived members of a 
clade
share with members of other clades.  This is what we're forced to do 
with
pterosaurs.  (And bats as well.)


> That's a very bad
> sign when the 'preferred' cladogram can't nail
> down a sister taxon.


It does indeed give us a sister taxon.  Pterosauria (or a 
_Scleromochlus_ +
Pterosauria clade) comes up as the sister taxon to Dinosauromorpha.  A 
cladogram
will always provide a sister taxon (more than one in the case of a 
polytomy).
The issue here is the degree to which the recovered sister taxon helps 
elucidate
the ancestral morphology or ecology of pterosaurs.  So far, it hasn't 
helped a
great deal.  But that's not the fault of cladistics, or of Hone and 
Benton; it's
the fault of the fossil record, which hasn't yet yielded basal 
pterosaurs.


> Yes! Tim, good work!
> If you're referring to Pteromimus, it is indeed related
> to pterosaurs. It's a langobardisaur The first one
> recorded for North America, but cladistically its
> pre-Cosesaurus but it shows they too had an antorbital
> fenestra. Very important.
>
> If Procoelosaurus is also on your Tecovas list, it's a
> basal croc. Both interesting specimens.


Yes, I was referring to 'Pteromimus' and 'Procoelosaurus'. Interesting 
stuff
regarding their respective affinities - though I look forward to 
something on
this in the published literature.  From what you say of _Pteromimus_, I 
wonder
how much material potentially overlaps with _Protoavis_.


> Yes, you're right, but let's take it up a notch.
> Forelimb length is about 100% of the hindlimb length in
> Archaeopteryx. i'm still wondering, what is the
> explanation for such an extension on this taxon -- or any
> pre-Archaeopteryx taxon -- with such elongated forelimbs,
> non-supinating/pronating antebrachia and trenchant manual
> unguals if not for arboreality?


Two other alternatives:

(1) Prey capture.  Longer forelimbs allowed increased reach.  Targeting 
large
prey that was grasped with both hands allowed a decrease in 
supination/pronation.


(2) Gliding (or some other form of non-powered aerial locomotion).  
Longer
forelimbs allowed a larger flight surface, and the arms were used for 
climbing
vegetation.  This is partly concordant with your scenario.


I'm not necessarily advocating either of these scenarios.  I'm only 
saying that
alternate hypotheses to arboreality/brachiation do exist as an 
explanation for
further forelimb elongation in the line leading to birds.


Cheers

Tim