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RE: Who says dromaeosaurs can't fly?



Greg Paul wrote:

> That Cryptos arms were somewhat shorter than its exce[tionally long 
> legs means nothing since the arms of another living predatory avepod, 
> the secretary bird, are far shorter than the legs. 

I would query this analogy.  In the secretary bird (_Sagittarius
serpentarius_) the greater length of the legs relative to the wings is due
principally to the extraordinary elongation of the distal hindlimb.  This
bird spends most of its waking hours walking on the ground, stalking
terrestrial prey.  As a neornithine bird, the femur is largely decoupled
from stride generation, and so it falls to the distal hindlimb elements to
provide the bird with an elevated sensory platform.

BTW, I'm not necessarily contradicting the idea that _Cryptovolans_ was
volant.  I just think comparing dromies with modern cursorial birds is
apples and oranges.  Both have vastly different evolutionary pedigrees.


> As Steve notes sinornithosaurs may have been big winged fliers. If
> anything  the arm was longer relative to the body, and they have the 
> robust, flattened central finger and bowed outer metacarpal suitable 
> for supporting large primaries. 

Again playing Devil's Advocate... is the presence of "robust, flattened
central finger and bowed metacarpals" necessarily due to powered flight?  I
know the ecomorphological rationale: These features allowed firmer
attachment of the primaries so as to better resist torsional forces during
flapping flight.  

However, the suite of features seen in this array of dromies can also be
explained by less demanding forms of aerial locomotion: i.e. gliding and
parachuting.  If these same predators continued to use their forelimbs for
the capture and processing of prey (such as in the "death from above"
scenario you mentioned), this could provide a selective mechanism for a
stronger attachment of the primaries to the forelimb skeleton - particularly
in the manus/carpus region.  The dino-bird wouldn't want its primaries to be
detached by struggling prey.

The evolutionary scenario you present is entirely plausible.  I'm just not
convinced that it's necessarily superior.  I just would like to point out
that there are competing scenarios that are equally congruent with the
available evidence.

Fire away!



Tim