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Re: ADV: RE: Evidence For a Feathered Velociraptor...



On Tue, Sep 25, 2007 at 10:08:42PM -0500, Tim Williams scripsit:
> 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.

I'm not talking about flight loads, just 'forces exerted by air'.

> What I'm saying is that there may be other explanations beside
> 'aerodynamic load' as to why _Velociraptor_ has quill knobs.  

Can you think of a substantial load on a feather that isn't aerodynamic?
(in the 'forces exerted by motion through air' sense.)

All the contour feathers seem to do OK without extra anchors, and while
I suppose one could postulate fishing by dangling arm feathers in the
water or something, I don't see anything that makes this at all likely.

> 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.

Urm... I think I see the difficulty.

Aerodynamic load has (as I'm using it) nothing to do with flying.  It
has to do with forces exerted by moving the feather through the air.

Given remiges, there would be aerodynamic forces acting on them.  Given
the quill knobs, we can postulate substantial aerodynamic forces, but I
am not hypothesizing about what generated those forces, only that they
were present.

> > 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.

That's one arm caught in the beak, though, and one foot stuck in the
throat, and I take that example as the _Velociraptor_ having plain
honest lost.

That's not an example of a cling-and-bite or hook-and-claw strategy;
that's either (depending on order of events) a failed predation attempt
because the _Protoceratops_ didn't die fast enough to prevent it from
killing its attacker or a desperate attempt by the _Velociraptor_ to get
free after an aggressive defence resulted in the bit arm.

I favour the first scenario just because the _Velociraptor_'s trapped
forearm isn't severed, and I would expect that a not-yet-throat-torn-out
_Protoceratops_ beak would successfully sever the arm.

> 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.

I'll happily go with attacking, but I think it went very badly for the
_Velociraptor_ _because_ it got claws stuck, rather than being able to
complete a slashing attack.

> > 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.

There could, but I'm having a heck of a time coming up with any.

> 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.

Tussles with prey would not produce a plucking moment, though; the
geometry for that doesn't work out.  And if there's a general plucking
moment involved in prey interactions, what makes remiges special?  Why
is not the entire velociraptor denuded of its feathers?

> > 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 _Velociraptor_ did.

True, but the mechanisms available to _Velociraptor_ (and relatives) are
very similarly anatomically constrained; arguably more constrained, in
terms of forelimb motions.

> > But the 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.

Whups, yes.  Sorry.

> > 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.

I have been assaulted by geese; also ducks, and threatened by swans.
(Redwinged black birds, so far as nesting season goes. :)

Geese don't see needing those wings to fly with as any reason not to hit
you with them, frequently and violently.

Thinking about it, this does sometimes dislodge covert feathers.

-- Graydon