Re: Pro(to)avis

[Tim Williams <twilliams_alpha@hotmail.com>]

First of all, a correction.  I wrote:

> J.P. Garner, G.K. Taylor, and A.L.R. Thomas. 1999. On the origins of birds: 
> the sequence of character acquisition in the evolution of avian flight.  
> Proceedings of the Royal Society: Biological Sciences.  
> 266(1425):1471-2954.

The page nubers should be "1259-1266".  So the article is 8 pages long, not 
1483 pages long.  Quite a difference.  (I'm not sure where I got "1471-2954" 
from.)

James Cunningham wrote:

> In 4-winged birds, the tip fan is capable of supporting the weight of the 
> tail, but at first blush doesn't appear suited for also supporting the 
> weight of the legs, so without the hindlimb feathers those birds would also 
> have had a a bit of a cg problem.

It is my understanding of such things (which is not that much) is that a 
posterior center of gravity (cg) is a problem for pasive (non-powered) 
gliders as well as active (powered) fliers.

> Note that none of this applies to modern birds with brains evolved for more 
> unstable flight and without the weight of a long, unfeathered tail.

One curious aspect of avian evolution (at least, curious to me) is that the 
shortening of the tail and development of a pygostyle occurred in birds that 
had rather long legs (e.g.,_Sinornis_).  I think one of Gatesy's papers 
discusses this too.  So early ornithothoracine birds dispensed with the tip 
fan, but kept their "primitive" theropod legs.

Also, wouldn't the long tail-frond and hindwings have interfered with a 
running take-off?

> P.S.  Gatsey & Dial do good work.

That they do.

Phil Bigelow wrote:

> Perhaps the new view should instead be considered a third hypothesis,
> rather than being considered a replacement that falsified the earlier two
> hypotheses.

I didn't mean to imply that either the 'ground-up' or 'trees-down' 
hypotheses had been falsified.  No, what I was trying to say is that many 
traditional pre-flight models have been constrained by the perception that 
the proavian either spent all of its time on the ground, or all (or most) of 
its time in trees.  This did not help the formulation of individual 
pre-flight models.

Cheers

Tim