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Bats and Archaeopteryx



To L. Smith: Thanks for the info on bats. I too was wondering about their 
evolutionary development with regards to flight. I was also wondering if 
there has been any evidence in their fossil record  (scant as it is) to 
show that they evolved from a gliding form (through the stages that you 
list, ie. fingers becoming longer and incorporating into the wing structure)?
Also, have there been any studies done comparing the flight energy 
needs/consumption between bats and birds? Don't bats require/expend more 
energy than birds for flight?

RE. Archaeopteryx: Hmmm, let me try to rephrase my questions on this. My 
question is simply one of whether the evolutionary pressure from an 
arborial gliding existence would tend toward a bird-like wing development 
or a flying squirrel-like skin-flap development. Extant arboreal gliders 
all use the skin flap method. We have no modern analog to show that a 
bird-like wing can be derived from this (or that a bird-like wing will 
even evolve in an arboreal species). None of the modern gliding 
animals is even in an interim state of development <towards> the wing 
structure that birds have. 

The tendency in extant arborial glider development has been to 
develop characteristics that are already present in the animal (ie. 
webbing between limbs/body or fingers, etc.). In which case, it seems 
reasonable to assume that even if proto-Archie took to the trees at some 
point, that the wing-type seen had already begun to develop somewhere 
else. Archaeopteryx itself may have been a tree dweller (it probably 
could have functioned equally well on the ground AND in the trees 
since there are benefits to be derived in both environments [and 
therefore a great pressure to develop the wing further]).

Another question is in regard of the tucked wing position. Extant 
tree-dwelling gliders sprawl themselves out to bring their center of 
gravity closer to the tree. They don't tuck their front limbs close to 
the body. Tucking isn't likely to occur as long as you are climbing the 
trunk of the tree. However, once you have started to develop a tucked 
limb position, you can still hop up into the lower branches. Now, correct 
me if I am wrong (or my facts out-of-date), but I seem to recall that 
Archaeopteryx limbs were pretty-much tucked in (like a birds) but with a 
greater range of motion. This would lead me to suspect that they had at 
least evolved out of the trees, and (if Archies were tree dwelling) moved 
there subsequent to the development of the wing-limb.

Now, IF the structures were already present prior to tree dwelling, they 
most likely were used to the greatest advantage (which would include 
stabilizers for sharp turns, added lift on jumps/hops, etc. All of which 
are perfectly good flight precursers) while on the ground. Once in the 
trees, the evolutionary advantage may have been ENHANCED and thus develop 
into what we see today, but the beginnings, I believe, started on the ground.

Shaun Sinclair
        ssinclai@gpu.srv.ualberta.ca