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Re: Haplocheirus and Gregory S. Paul



Mark Pauline <markpauline@rocketmail.com> wrote:

> I'm sorry, that was imprecise of me.
> I must not have meant BCF but, rather, Mr. Paul's hypothesis
> that at least the most derived maniraptorans descended from
> an ancestor with flight capabilities superior to those in
> Archaeopteryx. 


No worries.  GSP's hypothesis has moved into the mainstream, at least as far as 
the concept of secondarily flightless ("neoflightless") deinonychosaurs is 
concerned.  By contrast, BCF (proposed by G. Olshevsky) has all but 
disappeared.  

However, the notion of "neoflightless" deinonychosaurs is not the most 
parsimonious explanation for the character distribution seen across Maniraptora.


> What would we call this, the Secondarily
> Flightless Maniraptoran hypothesis?


Neoflightless hypothesis,  or just "2F" is the usual parlance.


> As for Oviraptorosaurs and Therizinosaurs, the most
> primitive known members of both groups have fewer, rather
> than more, features in common with birds than their derived
> members, suggesting that their ancestors were not
> aerodynamic. 


I think you raise an important point here.  However, I think it is a mistake to 
equate "bird-like" with "aerodynamic".  The features that certain non-avian 
maniraptorans have in common with derived birds are not always directly 
associated with flight in birds or if they are, they may not have evolved for 
that purpose.

Further... osteologically speaking, _Archaeopteryx_ is not very aerodynamic.  
The musculoskeletal anatomy suggests that it was an exceedingly poor flier.  So 
I think it's possible for basal oviraptorosaurs (though not short-armed 
_Caudipteryx_) to have had some aerodynamic ability, so long as (a) they were 
small; (b) they had the ability to reach an elevated platform for launches 
(e.g., climb trees); and (c) their integument conferred drag and/or lift. 


> The recent paper by Balanoff
> et al. on Incisivosaurus demonstrates that the most bird
> like features of derived Oviraptorosaurs are convergences,


While this is true (for the most part), not all of these "bird-like" characters 
are necessarily related to aerodynamic behavior in oviraptorosaurs.  


For example, we do not know why _Nomingia_ has a pygostyle-like tail; but 
there's no reason to assume that it had an aerodynamic purpose.  The basal 
therizinosaur _Beipiaosaurus_ had one too.


Ditto the fused carpometacarpus of _Avimimus_ and _Heyuannia_: the fusion of 
these elements (also seen in alvarezsaurs, as well as in birds) probably had 
nothing to do with aerial locomotion in these particular oviraptorosaurs.


Cheers

Tim