[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: Campbell's even crazier than a MANIAC? (archeopteryx



Just nitpicking here:

> But note the exponential increase in air speed
> culminating in terminal velocity experienced by
> gravity-driven animals. 

Acceleration by gravity is roughly constant (initially, before approaching 
terminal velocity), not exponential. Airspeed increase is not exponential. The 
increase in the force of the relative wind, and the kinetic energy of the 
falling animal, do increase exponentially however.

Still, a leaping animal would essentially begin with a ballistic trajectory, 
and I have a hard time imagining an intermediate structure that would be 
advantageous. I would think a leap would lead to low drag structures and 
forelimb positions.

Whereas for a small enough animal, simply being "shaggy" will slow the fall 
enough from any height. For a larger animal, "shaggy" extended limbs could slow 
the fall, and lead to stiffer arm feathers to allow the arms to slow the fall 
more.
As a consequence, because the presumed intermediate just adopted a high drag 
fall position, and was bipedal, I would doubt the hindlimbs could splay to slow 
descent any usefull amount, and were probably held underneath as shock 
absrobers.

As its ability to glide rather than fall increased, andtime spend in the air 
was increased, and legs weren't immediately needed to be positioned as shock 
absorbers, I could see the hindlimbs performing an aerodynamic function as in 
Micro, but I would still think the ancestral initial slow faller/glider would 
have only forelimb wings.
Likewise, a powered flight first ground runner - i would expect forelimb wings 
to be the ancestral condition.

Also note the extreme importance of size here, and the surface area vs mass 
ratio.
Insect pro-wings may have evolved for skimming the water surface, but any dino 
is far to big to get any benefit from surface tension.

Likewise, insects are generally far too small to be killed by a fall - some 
ants glide by adopting freefall positions not unlike a skydiver - the 
difference being the ant survives landing, and the skydiver dies if he doesn't 
have a more substantial aerodynamic surface.

The barriers and acceptable intermediates for flying on such a small scale 
aren't really applicable to vertebrate flight.

If its not gliding/slower falling before powered flight, what good does a 
stubby wing with stubby feathers do?
WAIR? how would that behavior start with normal forlimbs?

Heck... even cats (larger than archie) spread their limbs out enough to slow 
and stabilize their fall, such limbs would never be suited for WAIR(assuming a 
biped with a size similar to a cat, and similar thickness limbs and feathering 
of a draq equivilant to a short or long hair cat).
Granted some cats have rather loose skin near their hindlimbs that will spread 
somewhat, and some rather long fur.
The point it they exhibit a behavior that benefits from aerodynamics, with very 
little adaptations, that is completely unsuited to WAIR or anything resembling 
powered flight.

I just cannot imagine evolution acting on anything aerodynamic in a terrestrial 
ancestor without preexisting aerodynamic adaptations, unless that ancestor is 
falling (be it a cliff or tree)