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Re: Evidence For a Feathered Velociraptor...



Er, I think Tim is correct in that load is load, and whether it is aerodynamic 
load or grasping thorns or whatever that is the load of origin, it works. What 
is most probable is debatable, and as usual I lean firmly to the side of "yes".

Keeping in mind that I haven't followed this as closely as I should before 
commenting -- 

One thing interests me that I haven't noticed being mentioned; if I understand 
the function of "quill knobs" correctly, that function implies stiffness of 
feather, which in turn implies that feather stiffness came first. So, ignoring 
momentarily the aero/thermal/display scenarios for feather stiffness; could it 
be that quill knobs are actually 'spine knobs', spines being useful in all the 
predation/combat scenarios mentioned? Is preservation good enough in the 
fossils mentioned to rule spines out? 

Don

----- Original Message ----
From: Tim Williams <twilliams_alpha@hotmail.com>
To: dinosaur@usc.edu; oak@uniserve.com; twilliams_alpha@hotmail.com
Sent: Tuesday, September 25, 2007 11:08:42 PM
Subject: RE: Evidence For a Feathered Velociraptor...


Graydon wrote:

>> I can understand why quill knobs imply structured feathers, but not
>> aerodynamic load.
>
> Because that's what quill knobs _do_,


Well, that's what quill knobs do in _modern_ birds.  But, as with many 
avian/avialan characters, the reason why quill knobs first 
evolved may not be the same reason as why modern flying birds have quill knobs. 
 Exaptation, in so many words.


What I'm saying is that there may be other explanations beside 'aerodynamic 
load' as to why _Velociraptor_ has quill knobs.  
I'm not arguing that the quill knobs have _no_ function in _Velociraptor_; I'm 
merely arguing that the function of quill knobs in 
_Velociraptor_ may not be associated with aerial locomotion.  If the latter is 
true, this non-aerodynamic function may have been 
the original function of quill knobs, which were later exapted toward 
aerodynamic load in the line leading to birds.


> If the feathers are being flapped through the air, at speed, for
> whatever reason, they're going to be under aerodynamic load. It doesn't
> matter if it's leaping to claw something's face off or fanning the nest.


Yep, fair enough.


> That only works if there _were_ such tussles, and I don't think there
> were. It's a bad idea to wrestle if your advantages are being fast and
> spiky and you're smaller than your prey animal.


And yet, one _Velociraptor_ skeleton was preserved locked in a deadly embrace 
with a _Protoceratops_ skeleton.  So this 
particular tussle is more than just hypothetical.


Carpenter, K. (2001).  Evidence of predatory behavior by carnivorous dinosaurs. 
 Gaia 15: 135-144.


Although other interpretations have come up for this pose (e.g., the 
_Velociraptor_ was scavenging a _Protoceratops_ carcass; 
the _Protoceratops_ was the aggressor), the most plausible explanation is that 
the _Velociraptor_ was attacking the 
_Protoceratops_, and used its forelimbs (as well as its hindlimbs) to engage 
its prey.


> But I don't think it _is_ a correlation between quill knobs and powered
> flight. I think it's a correlation between quill knobs and aerodynamic
> load on retrices.


I would go a little further and say it's a correlation between quill knobs and 
the need to securely hold the remiges in place.  That 
is, aerodynamic load is one possible force that acts against the remiges; but 
there could be others.  The need to hold the 
feathers in place during tussles with prey (especially large prey) is one 
possibility.  BTW, the two factors (aerodynamic load & 
predation) are not at all mutually exclusive.  I'm not saying you're wrong.  
I'm just saying that other factors beside 
aerodynamic load deserve consideration.


> We know there are other ways to deal with feather control and anchoring,
> because there are modern volant species as don't have quill knobs, but
> the presence is pretty tightly correlated with keeping anchored against
> airflow.


Yes, but no modern bird uses its forelimbs as specialized instruments to grasp 
or kill prey.  Not like _Velocir
he quill knobs are expensive, and we know that other linages of
> velociraptorin theropods lost them, so some sort of developmental lock
> isn't the least hypothesis; the least hypothesis is that they were used
> to support retrices under aerodynamic load.


For sure.  (Although I think you mean 'remiges' rather than 'rectrices'.  I 
don't mean to be pedantic, but the tail feathers are a 
whole other box and dice!)  I don't believe in a developmental lock either - 
not for quill knobs, anyway.


> I can tell that you, personally, have not been assaulted by geese. :)


Nor me.  Just a bad-tempered emu.  And a few overprotective magpies during 
nesting season.


> My personal guesses are intraspecies competition for leap height, and
> predation advantage by assisted leaping out of the plane of the ground.
>
> No idea how to test any of that, and as you say, highly speculative.


Nothing wrong with that!


Cheers

Tim
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