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

[Tim Williams <tijawi@yahoo.com>]

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