Re: To Sprawl or Not to Sprawl?...

[Jeff Hecht <jeff@jeffhecht.com>]

At 5:18 PM -0500 5/5/04, Tim Williams wrote:
> > Since the feathers could have been useful without employing them 
> > horizontally (e.g. rudders), there is no evidence right now to 
> > support the sprawling M. gui idea.
>
> Yes, these "butt-fans" could have been useful as rudders for 
> parachuting or gliding theropods.  Also, it may not be necessary for 
> the hindlimbs to be laterally-oriented in order to provide a surface 
> capable of
> generating lift during aerial leaps or glides.  I think further 
> biomechanical analysis is required to establish whether these 
> hindlimb-wings could have been used as a gliding surface, and could 
> be held approximately coplanar with the forelimb-wings.  Until that 
> work is done, I'm keeping an open mind.

That raises the question of how wide would the hind limbs have to be 
splayed to provide some lift. Evolution involves biomechanical 
compromises such as trading off agility on the ground for agility in 
the air. How long would it take for Microraptor - or some earlier 
taxon - to evolve hind limbs that could be splayed enough to glide? 
-- Jeff Hecht