RE: Archaeopteryx not the first bird, is the earliest known (powered) flying dinosaur

[Tim Williams <twilliams_alpha@hotmail.com>]

Gregory S. Paul wrote:

> Because winged
> dromaeosaurs have even better muscle attachments, more chest and arm 
> strength,
> and bigger more firmly attached primaries, they must have been even better
> powered fliers. To argue otherwise does not sense make.

Nevertheless, that's what I'm about to do.  :-)

You could indeed be correct in asserting that all of these features you 
mention are directly flight-related.  However, alternative hypotheses should 
not be dismissed, and could even be explored further.  For example, having 
longer arms that were capable of great strength could be associated with 
improved prey-catching behavior, especially grasping and holding prey.  
After all, theropods began as bipedal predators; so adaptations that improve 
the adductive/abductive strength of the forelimbs and/or extend the reach of 
the hands should not be automatically assumed to have an aerodynamic purpose 
simply because these taxa are phylogenetically close to birds.  These 
anatomical changes may have made it easier for the theropod to grab and hold 
onto prey.  Similarly, the wider base of the second finger, and the stronger 
attachment of the primaries it implies, may simply indicate that the 
forelimbs continued to be used for prey capture, and this required a firmer 
attachment of the feathers to resist being torn out by struggling prey.

I'm not claiming that the ideas I raised are actually correct.  But by the 
same token, I don't think we're quite ready to throw the baby out with the 
bathwater and abandon every idea on the origin of avian flight that's 
appeared over the past 20-30 years.  The predation-to-flight model has both 
phylogenetic and biomechanical support.

> Also severly damaged is the hypothesis that the flight features present in 
> flightless deinonychosaurs and other derived theropods are preadaptations 
> for flight. The arguments for folding arms, big sternal plates, pterosaur 
> like tails and so forth having evolved for nonflight purposes and then 
> being utilized for flight were always driven by cladistics rather than 
> functional logic and are now obsolete unless we find Jurassic theropods 
> that clearly evolved these
> things before flight appeared.

Again, playing the role of gad-fly... I would say that having ALL these 
features evolving specifically for flight strikes me as teleological.  In my 
mind, if you're going to evolve from a non-flier into a powered flier there 
has to be some raw material for evolution to work on - and I think having 
long arms and strong muscles to work them are good pre-flight adaptations 
that provided a template for exaptation toward powered flight.

BTW, I know that many (most?) theropod experts believe that all 
maniraptorans could fold their forelimbs in a bird-like fashion, but it's 
well worth reading Carpenter (2002) for a contrarian view:

Carpenter, K. (2002)  Forelimb biomechanics of nonavian theropod dinosaurs 
in predation.  Senckenbergiana Lethaea 82: 59? 76

> One thing we do know is that the notion that flight evolved in a simple 
> linear progression from the "Protoavis" to perigrine falcons has been 
> demolished. All sorts of evolutionary experiments and reversals were 
> probably going on. '

Yes, this I agree with completely.

> I have not seen a Jehol dromaeosaur with a truly cylinderical femoral head 
> like those seen in the > flightless velociraptorines, they are always 
> somewhat more rounded in shape. This indicates that
> the winged dromaeosaurs could splay their legs out much more than normal in 
> theropods, although not necessarily entirely flat. This makes sense since 
> they had leg wings. I find attempts to explain how these hindwings were 
> deployed without sprawling the legs highly dubious.

I wish we could be so confident on this point.  It's my understanding that 
you need more than just a non-cylindrical femoral head (i.e., one that is 
spherical or subspherical) to achieve a sprawling hindlimb posture.  The 
animal would need to modify the hip-socket (acetabulum) that actually 
receives the femoral head, as well as undergo a complete overhaul of its 
pelvic musculature.  Furthermore, studies on living primates show that while 
a subspherical femoral head certainly increases femoral abduction, a more 
cylindrical femoral head allows for better landings.

Cheers

Tim