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RE: Senter 2006, Confuciusornis, and humeral mobility




--- Jaime Headden <qi_leong@hotmail.com> schrieb am So, 27.3.2011:

> Von: Jaime Headden <qi_leong@hotmail.com>
> Betreff: RE: Senter 2006, Confuciusornis, and humeral mobility
> An: "Jason Brougham" <jaseb@amnh.org>, "Dinosaur Mailing List" 
> <dinosaur@usc.edu>, "Tim Williams" <tijawi@yahoo.com>
> Datum: Sonntag, 27. März, 2011 10:31 Uhr


> Both antecedents and decendents in the Avialae to
> *Confuciusornis sanctus* have stubbier, lower-aspect, and
> rounder wings, and longer tails, more distinct retricial
> arrays (or whatever term is suitable for *Archaeopteryx
> lithographica*) and very divergent arm, shoulder and pelvic
> anatomy.

I would rather say "older" and "younger" taxa. 

That is not to imply that Confuciusornithidae are widely separate from other 
avians (as per some BANDit theories, I think Kurochkin favors a BATBAND theory 
in which only some avians are descended from theropods). 

Rather, it seems to me that confuciusornithid ancestors some time in the 
mid-late Jurassic by some chance evolved incipient states of the autapomorphies 
Jaime described. Consequently, their flight apparatus became something that is 
quite unique and (as far as we know) did not manage to evolve much further.

In aviation terms, they might be considered something like the 
http://en.wikipedia.org/wiki/Coandă-1910 - surprisingly advanced in some 
features, but with an overall bauplan that had not been streamlined for flight 
enough for these advanced features to make a long-term difference in survival 
vs extinction.

Another (somewhat more conventional, but still not clearly related to either 
modern birds or Enantiornithes) distinct approach was followed by 
Omnivoropterygidae. 

I think we cannot as of now be sure what exactly happened around 150 Ma, and 
how the different "avian" lineages that emerged around that time and evolved 
flight capabilities relate to each other. The physics of getting airborne are 
quite tough on an organism; I expect homoplasies to be rather frequent. Or 
perhaps rather a general trend to evolve highly similar features than strict 
homoplasies. 

This trend ended in the early Cretaceous, this much is evident. But I am not 
sure whether the mid-late Jurassic ancestors of _Confuciusornis_, _Sapeornis_, 
_Enantiornis_ and _Passer_ would have looked as distinct as they might have 
been. Cladistic analyses may be not entirely dependable, but phenetic analyses 
would, of course, be certain to fail in such a situation where overall 
similarity exceeds closeness of relationship. 

--------

One might pay more attention to biogeography, remove Archie from the analysis. 
I wonder what happens if only East Asian taxa are used. Nobody knows whether 
Archie is not simply too "generic" and will cause taxa to clade that shouldn't 
as long as Archie's. Especially what happens to the Scansoriopterygidae in such 
a case (and to other "almost-birds" such as the Chinese "long-tailed" 
assemblage of _Dalianraptor_ et al) would be highly interesting to find out. 
Particularly _Jixiangornis_ needs to be watched; it has a tendency not to clade 
with the other longtails as it seems, but this is if the excellent hypodigm 
from Archie is included.


Regards,

Eike