Re: Gliders to fliers

[rjmeyer@ix.netcom.com (Rob Meyerson)]

During this discussion on the evolution of powered flight, there is an 
important question that needs to be asked.  But first, let me state the 
premises for my argument (I will use pterosaurs to make my point; I propose 
that the same basic ideas will coorespond to dinobirds).

1)All powered flight needs to start from a jumping and/or gliding lifestyle.

2)The flying squirrel is a good model for the gliding-phase in bat evolution.  
The continuous flap of skin from fore to aft in the squirrel can easily adapt 
to the wings of the pterosaur (I will use the trees-down theory for this line 
of reasoning).

3)In the squirrel, the forelimbs are roughly equal in strength to the 
hindlimbs.  During gliding, all four limbs are equally used for course 
adjustment and to maintain control.

4)For powered flight, the forelimbs evolve to take full control of all flight 
needs: speed, direction, lift, etc.

My question: how does a critter go from 3 to 4?  What environmental stresses 
and what selection pressures are present in a glider lifestyle that would 
"force" a glider to develop fully powered flight?  Could a thinning forest, and 
larger distances between trees, provide the needed pressure for the transition 
powered flight?


Rob Meyerson

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