Re: Fw: Dinosaurs and birds

[MICHAEL HABIB <habib@jhmi.edu>]

> No, I don't. As the car accelerates (w/in reason), I give a little 
> jump, and make some progress, effectively increasing stride length. 

Sure, but only within a pretty narrow margin.  If you are sprinting at your 
fastest speed, the extra pull of the car shouldn't help much.  If you start 
having to sacrifice stride frequency to increase the stride length, then you 
won't really be making any progress.  Keep in mind, as well, that the analogy 
isn't perfect.  If you're very agile, you might be able to keep up with the car 
by essentially bouncing briefly off the ground every so often and letting the 
car pull you through the air.  That's not really running with extra thrust, 
though, that's just being dragged with style.  I'm impressed that you've tried 
though, it would make me a tad nervous.

In any case, the point Jim was trying to make is that the speed of a running 
(bipedal) animal is largely limited by mechanics of the hind limbs and their 
interaction with the ground.  Adding thrust from the forelimbs will only add 
speed if the hind limbs can keep up.  They generally cannot if the animal is 
already at a sprinting gait, so forelimb-assisted speed increases don't tend to 
be very feasible for birds.  This is one reason why running birds don't deploy 
the wings unless they are launching, or engaging in a ground maneuver for which 
an additional force vector might be helpful in maintaining balance.

>>  BTW-- did you notice that Mike H. actually admitted I was (at least 
> in theory) right in that inclines are not essential to wing-assisted 
> evo-scenario's? It was buried pretty deep, but it was there. Ha! 
> Although 'fore-limb assisted' is a better term, 'wing' being the end 
> result of the process...

It was never meant to be "buried".  You are most definitely correct that 
inclines are not theoretically required for cursorial-based wing evolution.  
They *are* required for a WAIR type mechanism; ie. a cursorial mechanism by 
which forward progress is directly enhanced by wing oscillation, which is all 
my original post was meant to imply.  That does not rule out maneuverability 
and balance being enhanced by forelimb dynamics over level terrain, and these 
will obviously bolster forward progression indirectly.

Cheers,

--Mike H.