Re: Dinosaurs and birds

[Tim Williams <twilliams_alpha@hotmail.com>]

Michael Habib wrote:

> If the animal is running on a level substrate, then producing a lift force 
> is usually not particularly helpful, and can actually be counter-productive 
> under some scenarios (as would probably be the case for basal birds).

Would a lift-force when running on a level substrate be useful for a 
pre-avian stage?  For example, would it be useful to a small theropod that 
was chasing flying insects and trying to snatch them with its jaws?  I'm 
thinking of the 'ground-up' model of Caple et al. (1983), under which a 
cursorial "pro-avian" biped uses its forelimbs (incipient wings) as an 
airfoil for balance and stabilization during brief leaps into the air.

Reference:

Caple, G., Balda, R.P., Willis, W.R. (1983). The physics of leaping animals 
and the evolution of preflight.  American Naturalist 121: 455-476.

I agree that WAIR would only be useful in trunk-climbing in a bird that 
already has a fairly powerful flight apparatus.  Probably beyond the 
_Archaeopteryx_ stage.

Jeff Hecht wrote:

> This may be more relevant to Microraptor than Archaeopteryx, but a while 
> back somebody pointed out to me that climbing up a tree can be much easier 
> than getting back down. Just ask anyone who's had to rescue a cat.

Some gliding mammals can climb up trees quite well, although they are not 
particularly good at negotatiating branches, and never have need to climb 
down courtesy of their gliding adaptations.  The Japanese flying squirrel 
(_Petaurista leucogenys_) is a good example: its stiff fingers and toes make 
it very ungainly in the tree-trops, but it climbs up trunks extremely well.

Cheers

Tim

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