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Re: Gliders to fliers
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
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
Is it good if a vacuum really sucks?