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Re: cursorial flapping -Reply

In a message dated 95-12-03 11:12:11 EST, longrich@phoenix.Princeton.EDU
(Nicholas R. Longrich) writes:

>       One preadapation towards flight that arboreality may cause is 
>developing the arms and putting them in the right position. I don't know 
>how constrained the movement of theropod arms are, but whenever I see 
>squirrels, I notice how sprawled out the legs are when they run over the 
>ground. When they get up in the trees, the arms spread wide to grip the 
>trunk. This puts the arms and legs in a perfect setup to develop a 
>glide-plane. One problem is that the motions employed are the opposite- 
>squirrel arms produce most of their power pulling backwards, while birds 
>produce their power an a forward, downward stroke. But what might develop 
>these muscles would be clmibing forward down the tree, instead of up, 
>and, once glide-plains are developed, the muscles to hold these in place. 
>The problem of course remains the flapping.

Indeed, part of the impetus behind BCF is my personal observations (casual
and not scientific, but real-life nevertheless) of squirrels in trees and how
they use their forelimbs, then extrapolating their movements to small
archosaurs of similar habits. It also explains how "flying squirrels"
probably evolved.