Re: Paedomorphosis ( Re: BARYONYX' CLAWS )

["Matthew Troutman" <m_troutman@hotmail.com>]

>> The form of secondary flightless that I argue against is the 
flightless 
>>is the one where some theropods had volant ancestors that went 
>> flightless. Since they lack the paedomorphic trends seen in birds, it 
>> seems unlikely that they had volant ancestors. I think that we have 
>>come to an understanding ( at least it seems so ). I think that it 
>>sounds that you you agree that no theropods had volant ancestors >>( 
at least it sounds like that ) because they lack the paedomorphic 
>>trends see in flightless birds.  

<<Right, if by volant you mean "capable of powered, flapping flight." 
There are, however, theropod lineages that diverged from the avian 
lineage quite close to the point from where _Archaeopteryx_ 
diverged--such as dromaeosaurids (including _Rahona_, which has the 
kinds of wings I and I'm sure Greg Paul before me envisioned for flying 
dromaeosauroids), alvarezsaurids, parvicursorids, oviraptorids, 
_Unenlagia_, and such. These could well have had >>volant< (by your 
definition) ancestors that resembled _Archaeopteryx_ in their flight 
capabilities. However, since we do not have a handle on just what kind 
of flying _Archaeopteryx_ did (whatever kind it was, it must have been 
different from that of modern avians, if only because of the aerodynamic 
properties of the elongate tail and the lack of a giant keeled sternum), 
we just have to wave our hands at this point. "Volant" it probably was, 
but justhow volant remains a matter of conjecture.>>

      I agree that these theropod lineages did diverge close to Rahona 
and Archie, but I doubt that they are directly descended from the. 
Archaeopteryx does show many volant ( flapping flight ) features that 
suggest an advanced level of flight ( large furcula, acute 
scapulacoracoid angle ).

<<Also--how about _Hesperornis_? Flightless by paedomorphosis? (Don't 
think so...)>>

     Maybe. Pasquiaornis shows more volant adaptations than Baptornis 
and Hesperornis. Based on its volant adaptations ( which suggest that it 
was close to being volant ) and the lack of volant characteristics in 
later hesperornids and the paedomorphic features ( vestigal humerus, 
lack of sternal keel ) seen in them, I think paedomorphosis is likely.

MattTroutman

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