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Re: Archaeopteryx and Flight

On Tue, 20 Dec 1994, Stan Friesen wrote:

> How about leaping from tree to tree?

Yes, I can can accept that (tree to tree leaping not being entirely 
uncommon among tree dwelling animals).I just have trouble with a limbed 
(and wingless) animal developing gliding (which hasn't developed a 
'wing'-like structure on any other animal (correct me if I'm wrong here, 
but give me some documentation if you do)) and then progressing to powered 
flight (which _does_ require a more-or-less specific limb/body structure 
[the previously mentioned keeled ribcage being one example; The tendon 
arrangement at the sholder joint being another]). The last time I 
checked, these structures were not readily derived from gliding 
structures due to the different type of use required of them (ie. the 
tendon arrangement required for powered flight is not required for 
gliding flight and therefore there is little evolutionary pressure in 
that direction).

 All the gliding (or tree leaping) arboreal 
animals that I can think of have developed skin flaps between fore- and 
hind- limbs (gliders), or have no wing-like structure at all (gibbons for 
example). But I don't know of any of them going on to develop powered 
flight OR wing-like structures subsequent to that.

> [Actually, for an animal a little smaller than Archie, a fall 
> from a tree would *not* be fatal - just painful, and potentially
> injurious].

Yes, this is true. And I will also agree that gliding style skin-flaps 
will (in addition to imparting gliding ability) add drag and help prevent 
more serious injury from a fall. However, wouldn't it still be 
evolutionarily more advantageous to not injure youself at all? Even 
non life-threatening injuries put a potential prey item at a 
disadvantage compared to one that has not sustained any injury.

I have a nagging feeling that this great evolutionary event came about as 
a result of a complex series of events, and that we may be trying to 
simplify it too much by reducing it to any single specific event 
(principle of parsimony notwithstanding).

Shaun Sinclair