RE: Evidence For a Feathered Velociraptor...

[Tim Williams <twilliams_alpha@hotmail.com>]

Mike Keesey wrote:

> Or, indeed, the idea that any coelurosaur with remiges (e.g._Archaeopteryx_, 
> _Microraptor_) is capable of powered flight.
> (Although we already knew that, thanks to _Caudipteryx_ and 
> _Protarchaeopteryx_.)
> Powered flight seems pretty secure for 
> _Ornithurae_/_Pygostylia_/_Avebrevicauda_. Beyond that, though, what
> do we really know? We have some stuff with wings, and many people assume the 
> small ones flew and the big ones didn't,
> but, for all we know, _Archaeopteryx_ may not be avialan (sensu Gauthier and 
> de Queiroz 2001). Or, conversely, _Avialae_
> might include most of _Maniraptora_.

I'm not at all keen on Gauthier and de Queiroz (2001)'s proposed 
apomorphy-based definition of Avialae: the presence of “feathered wings... used 
for powered flight.”  Seriously, how are we supposed to infer powered flight 
for fossil birds!  Especially when the first birds had a morphology very 
different to modern birds, with their long tails and puny sterna.  [Personally, 
I much prefer Senter's (2007) definition of Avialae, which is "all taxa more 
closely related to birds than to Deinonychosauria" (cf. Aves sensu Senter, "all 
taxa phylogenetically bracketed by _Archaeopteryx_ and Neornithes").]

Having said that, I agree that powered flight seems pretty secure for 
Ornithurae.  I also agree that the usual interpretation that taxa like 
_Archaeopteryx_ and _Rahonavis_ could fly, but microraptorines couldn't, does 
seem a little arbitrary.  It's really difficult to compile a list of 
exclusively 'flight-related' characters, given that many flight-related 
characters (a) precede the origin of flight (i.e., were exapted toward powered 
flight); (b) are retained in secondarily flightless taxa; or (c) evolved 
independently of Aves.  Characters such as the presence of quill knobs, or 
asymmetrical remiges and rectrices, appear no longer to be exclusively 
'flight-related'.  

It is really difficult to point to a character in _Archaeopteryx_ and call it 
100% flight-related.  You could find the same character in a microraptorine, or 
even a velociraptorine.  I suspect it's the overall 'gestalt' of 
_Archaeopteryx_'s morphology (both integument and skeleton) rather than 
individual features that pushes it over the line.  As Mike said, the size of 
the critter helps, given that _Archaeopteryx_ is below the cut-off for a flying 
animal (although I don't know quantitatively what the cut-off actually is), 
whereas velociraptorines and basal oviraptorosaurs (_Protarchaeopteryx_, 
_Caudipteryx_ are clearly too 'big', or have arms that are too short.  Also, 
_Archaeopteryx_ has only two wings associated with the limbs, as in modern 
birds (not four as in microraptorines) which makes comparison with modern avian 
flight easier.  

Graydon wrote:

> Seen that video of an eagle driving off a wolf? The eagle is (among
> other things) beating the wolf about the head with its wings.

Yes, but the eagle isn't trying to *catch* the wolf with its wings.  This is 
where the analogy breaks down.  For dromaeosaurids (or at least dromaeosaurines 
and velociraptorines) the forelimbs appear to have played a major role in 
catching and subduing prey.  And yet, _Velociraptor_ presumably had two 
featherdusters strapped to its arms.

> Geese and swans do that as a defence, or when having disputes with one
> another; all sorts of ducks do that, too. Feathers aren't that fragile.

True.  But in a battle between the beak of a desperate _Protoceratops_ and an 
arm feather, I think ther feather would come out second best.

> It's also not clear that the very limited range of motion in the
> maniraptoran manus was used for holding the struggling prey at all; the
> proto-flight-stroke looks more like a mechanism for slashing something
> apart.

That's a cool idea.  Has it been looked at in detail (biomechanics, etc)?

Cheers

Tim


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