Wings, predatory stroke etc (Re: birds DID NOT evolve from ther[o]pods)

["Tim Williams" <tijawi@hotmail.com>]

Couldn't wait to change that subject line...

David Marjanovic wrote:

> So wings evolved trees-down, the flight stroke whatever-up, and powered
> flight trees-down, all among scansorial* animals?

Here's what I think, in a nutshell:
"Feathers"  -   First evolved in terrestrial dinosaurs for insulation; later 
exapted for flight
"Flight stroke"  -  First evolved in terrestrial hunters, though in these 
the action was first used for predation, not flight (another exaptation).
"Wings"  -  Evolved in facultatively arboreal hunters for aerial locomotion.
Powered flight  -  Evolved in facultatively arboreal hunters.

The basic motion involved in the flight stroke initially evolved in 
ground-living, ground-hunting theropods.  Only, in these theropods, the 
motion was used to grab prey ("predatory stroke").  This motion was exapted 
for powered flight.  This is what Gauthier, Padian and others have been 
saying since the 1980's.  I still think they're correct.

You mention "wings".  One doesn't need a crystal ball to foresee a time not 
too far in the future where the definition of "wing" is going to come under 
close scrutiny, and be the source of considerable controversy - like we're 
currently seeing with the definition of "feather".  I'm not talking about 
_Longisquama_ here; but whether the arrangement of feathers along the 
forelimb of _Microraptor_, _Caudipteryx_ etc constitutes a "wing" (as they 
clearly do in _Archaeopteryx_).

That's a problem for another time.  Anyway, suffice to say, I think theropod 
forelimbs first took on an aerodynamic (aerial locomotive) function when the 
theropods themselves were sitting in (or clinging to) trees.  This prompted 
the "fuzz" (or "feathers" - see what I mean?) along the forelimb and manus 
to become differentiated from the primitive insulatory structures seen along 
the rest of the body.

I hope I didn't confuse you.

> * Finally found somewhere what "scansorial" means: able to climb and
> frequently doing so, but not necessarily arboreal at all, which means 
> living
> in trees. Cats (Felidae or suchlike) are scansorial but not arboreal.

I think leopards would qualify as arboreal.  I'm not familiar with the 
eclogy of the Felidae, but some other cat species may spend a lot of their 
time in trees as well.

By the way, the definition of "arboreal" becomes a little sticky with birds 
that spend most of their time on the ground, but fly up into trees only when 
they sense danger.  What we need is a ground-to-trees (or trees-to-ground) 
equivalent of "amphibious" (water-to-land, or vice versa).



Tim

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