Re: Third claw for climbing was Re: Pro(to)avis

[Tim Williams <twilliams_alpha@hotmail.com>]

David Marjanovic wrote:

> Again this depends on the orientation of the feathers. If they are all in 
> parasagittal planes, there isn't going to be much of an effect...

For the purposes of drag, I'm not so sure the precise orientation is 
important.

> But I've never liked the Pouncing Proavis idea, for other reasons. It 
> requires a rather small animal (if it's too heavy, feathered fringes won't 
> have enough of an effect).

To put the Pouncing Proavis hypothesis in it historical context, it was 
proposed at a time when _Caudipteryx_ was thought to be very close to the 
origin of birds.  Now, we have _Microraptor_ and possibly _Pedopenna_, both 
of which are closer to the base of the Aves than either _Protarchaeopteryx_ 
and _Caudipteryx_ (both of which are falling out as basal oviraptorosaurs).  
Microraptorans and _Pedopenna_ offer alternate ecomorphologies for 
pro-avians.  Then again, these four-winged gliders may have been an 
evolutionary dead-end and are just muddying the waters when it comes to 
reconstructing the origin of avian flight.

> Then it requires pretty large prey, because small prey is unlikely to stand 
> still (within a sufficiently small area at least) for long enough that an 
> incipient Pouncing Proavis would have any chance.

It think this is a slight oversimplification.  The 'pounce' may get the 
Proavis close to the prey, and it could run over the intervening distance 
with those cursorial hindlimbs.

> I prefer separate explanations. Wings for brooding, then exapted for... who 
> knows... WAIR or maybe even swimming or...

Swimming, a la Ebel's swimming-to-flight hypothesis?  It's an interesting 
model... but, nah, don't think so.  :-)

Cheers

Tim