Re: Archaeopteryx not the first bird, is the earliest known (powered) flying dinosaur

[Tim Williams <twilliams_alpha@hotmail.com>]

Hi Jim

> What is your line of reasoning?  I'm not arguing, I just don't know what it 
> is, having probably overlooked earlier explanations.

I guess I'm influenced by those enormous hindlimb feathers we see in 
sinornithosaurs - I cannot visualize a method of powered flight that would 
use all four limbs.  Again, maybe this reflects the limits of my imagination 
more than the constraints of powered flight.  Also, I tend to doubt that 
_Archaeopteryx_ was a good flier, which is why I'm attracted to the 'phugoid 
gliding' model.  Tom Holtz may be right when he suggested that 'true' flight 
evolved after _Archaeopteryx_ and sinornithosaurs, and these taxa represent 
early (and ultimately doomed) experiments in aerial locomotion.

To put it another way, GSP emphasizes that the flight adaptations of 
sinornithosaurs were no worse and probably better than those of 
_Archaeopteryx_.  But given that _Archaeopteryx_ set the bar very low, that 
isn't saying very much.

> >  However, I do not think it is wise to view theropod relationships solely 
> > through the prism of flight evolution.
>
> You got that right.  It bugs me that folks tend to ignore everything else 
> that was going on with these beasties, and the compromises and exaptions 
> being made.

Yes, the future contaminates the past.  We *know* that birds came to fly, so 
we tend to have that at the back of our minds when we look at the earliest 
birds and their close relatives.  GSP has a lot of great ideas (and he may 
be right!), but when he looks at taxa like _Sinornithosaurus_ and 
_Microraptor_ and _Archaeopteryx_ I think he focuses too much on what came 
to be rather than what was.

> > Maybe I'm being limited by my own imagination, but I do not see how being 
> > "small" and "long-armed" is enough for natural selection to act upon in 
> > order to convert a non-flier into a powered flier.
>
> It's sure a big help, because the far lighter wingloading means that small 
> gusts (or steady winds, if one or more feet are on the ground) have far 
> more impact upon the animal, and he will more often have to reconfigure his 
> body and/or arm positioning to cope with them.  If he doesn't, he's going 
> to limit his/her number of descendants.  Over a period of time, this will 
> lead to the survival of more descendants from those individuals who did it 
> better. Eventually you get a transition from non-flyers to flyers (note 
> that I'm not saying it happened this way, just that lighter loading and 
> longer arms make the transition both far easier and more necessary.  
> Perhaps necessary isn't the correct word; maybe facilitative.

Yes, but at the stage you describe, the animal must already be making forays 
into the air, of some nature at least.  The question I'm trying to get GSP 
to think about is "How did it all get started?"  In other words, even at the 
non-flyer stage the prospect of aerial locomotion must be selectively 
advantageous, and there must be some anatomical hardware for evolution to 
start moulding into a future flight apparatus.  I don't think this hardware 
(= incipient flight adaptations) needs to be involved in flight, or perhaps 
any kind of aerial locomotory behavior for that matter.

I agree with everything you say (and I understand that your model is *very* 
hypothetical).  But I'm thinking about the stage before, when wingloading is 
just a twinkle in the theropods's eye.

I hope that made sense.

Cheers

Tim