Re: Pro(to)avis

[Michael Habib <mhabib5@jhmi.edu>]

I agree that it is risky to assume that the legs could reach a full 
horizontal position (given that the specimens are crushed and that this 
would be an unusual trait for theropods).  However, there are other 
ways in which the long feathers present on the hindlimbs could be 
involved with flight.  Here are a few I can think of, I'm sure others 
can think of more:

1) The limbs may have been held subhorizontal, but still held close 
enough to a horizontal plane to generate lift.

2) The hindlimb feathers may have more important to increasing passive 
stability than to generating lift.  A number of different hindlimb 
orientations (other than splayed horizontal) might accomplish this 
goal, either by producing some differential lift laterally when the 
animal tilts, or by simply increasing posterior drag such that the 
animal had a tendency to stay facing forward.  (The problem with these 
ideas is that the increased drag would make it harder to stay in the 
air).

3) It could simply be a developmental constraint, or be unrelated to 
flight...but I'm not sure how to demonstrate these very conclusively.

Just a couple of thoughts,
--Mike

On Friday, September 16, 2005, at 06:16 PM, David Marjanovic wrote:

> ----- Original Message -----
> From: "jrc" <jrccea@bellsouth.net>
> Sent: Friday, September 16, 2005 6:56 PM
>
> > I would suggest that animals that had only a tip fan on their tails 
> > could be more likely than others to have hindlimb wings.  Animals 
> > that had a full tail (Archie) could be more likely to omit or 
> > minimise the hindlimb feathers.  It appears to me that the hindlimb 
> > feathers are likely derived to support the weight of the legs and 
> > long tail in those animals that have only tip fans, and that the tail 
> > carries that load in animals with full tails, so that there is no 
> > selective pressure toward hindlimb wings in full-tail animals.
>
> This makes a major assumption on the orientation and/or mobility of 
> the "hindwings"... the fossils are squished flat, deforming (and often 
> breaking) even the bones, so we should be very careful with that.