Re: Again: origin of bird flight

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

David Marjanovic wrote:


> True, but I disagree with the "Pouncing Proavis" hypothesis:
> 1. It's mantra time: There Were No Trees At Solnhofen. (I don't think >3 m 
> high bushes are suitable for such pouncing.)

I have read Viohl?s (1985) assessment of _Archaeopteryx_?s island domain 
(hardly an island paradise, I'm sure you'll agree).  This mantra only works 
if both _Archaeopteryx_ and every intermediate proavian that led to 
_Archaeopteryx_ lived in this habitat.

But to quote from Paul Buhler: ?The problem is that you can have a desert 
and an inland sea and still have a nice forest not too far away.  In the 
Solnhofen near Eichstatt they have found dragonflies and other aquatic 
insects.  That means that not too far away there must have been a forest 
present which was denser than the one documented in the fossil record.  So 
you cannot trust the fossil record in the immediate vicinity of the specimen 
to reflect the ecological situation of the entire surrounding area.?

This is especially true of _Archaeopteryx_: it could fly.  It would not be 
forced to remain on an island encircled by water.

Besides, _Archaeopteryx_?s ancestors need not have all lived in the scrubby, 
sparsely-vegetated environment of Late Jurassic Bavaria.  The proavians 
could have emerged in a more densely-forested area.

> 2. *Archaeopteryx* (and *Microraptor*, and even the larger
> *Sinornithosaurus* whose skull is only 13 cm long) surely didn't hunt >prey 
> that could be hunted this way. Insects, or, in the case of >Archie, fish 
> seem more probable (and *small* tetrapods in the case of 
> >*Sinornithosaurus*).

Small tetrapods are exactly the type of prey that I picture _Archaeopteryx_ 
hunting: frogs, lizards, etc.  It may have sighted them from a tree branch 
first, then leaped onto them.

Fish.  The diet of _Archaeopteryx_ (and its ancestors) may have included 
fish, but I don?t think fish made up most of its diet.  _Archaeopteryx_ 
lacked the procumbent front teeth of fish-eaters, and would have had to 
compete with rhamphorhynchids (which did have jaws specialized for 
piscivory).

Insects.  Again, _Archaeopteryx_ may have fed on insects, but I don?t think 
_Archaeopteryx_ was designed for catching insects out of the air.  Its jaws 
were too narrow.

So, fish and insects may have comprised a part of _Archaeopteryx_?s diet, 
but I don?t think predation upon either aerial or aquatic prey was the 
driving force behind flight.

> 3. The lack of tertiaries in Archie, and the fact that tertiaries in >birds 
> look like an emergency solution in the first place, is IMHO >evidence that 
> wings were originally used for something else than >flight;

I agree.  But the ?something else? I believe was drag and maneuverability in 
branch-to-ground leaps.  This is not flight.  Flight efficiency is less in 
this case than if the incipient flight structures had been positioned close 
to the body wall (armpit, base of tail).  Distally-located gliding surfaces 
do nothing at all for lift.

> IMHO much more probable, brooding! Have a look at a brooding
> oviraptorid; all known specimens have their inner arms closely >appressed 
> to the rib cage, while the forearms and hands are splayed >and suggest the 
> presence of wing feathers, (c) HP Hopp & Orsen 1998.

Yep.  That the proavian used the proto-wings for more than one purpose is 
entirely reasonable.

> I'm going to buy that dromaeosaurs may have dragged dead prey up a >tree 
> for safer feeding, like leopards do today and the picture at
> [snip] shows it, but not much more.

That?s a matter of opinion.  Personally, I like the notion of basal 
eumaniraptorans (and perhaps basal dromaeosaurids) being scansorial.


> The tail feathers of *Archaeopteryx* are symmetrical, unlike its wing
> feathers!!!

Are you sure of this?  I was under the impression that they were weakly 
asymmetrical.

> > Let's look at _Caudipteryx_.  It has primaries on the manus, but no
> > pennaceous feathers (remiges) on the forearm or humerus.

> AFAIK the wing feathers continued onto the forearms.

There are 14 remiges on the manus.  The original description o of 
_Caudipteryx_ does not mention remiges on the forearm.  But, reading through 
Zhou and Wang (2000), they mention secondaries (poorly-preserved).  I think 
it?s fair to say that the primaries of _Caudipteryx_ were the largest of the 
?wing? feathers, and tertiaries/tertials were absent.


> I'm sure symmetry is the plesiomorphy for feathers

I agree that, relative to asymmetry, vane symmetry is plesiomorphous for 
feathers.


> Fits underwater flight, too.

After reading Ebel?s paper, I found his ?swim-flap-fly? model very 
unconvincing.

> > The obvious terrestriality of
> > _Caudipteryx_ and oviraptorids, and troodontids (assuming a > 
> monophyletic
> > Deinonychosauria) and velociraptorines, would be secondary under this
> >scenario.

> Just a question here -- is there still anyone on this list who thinks > 
> that the abovementioned groups are not secondarily flightless? :-)

To clarify something which I admit might have been expressed rather 
ambiguously: by complete ?terrestriality? I mean lack of arboreality, not 
flightlessness.  I think velociraptorines and oviraptorids are 
non-scansorial, non-arboreal, while basal paravians/eumaniraptorans I 
suggest were scansorial and facultatively arboreal.  I do not think that 
velociraptorines and oviraptorids are secondarily flightless.


Tim


------------------------------------------------------------

Timothy J. Williams

USDA/ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163

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