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Re: Archaeopteryx and Flight

Ah, well...enough lurking. Time to step into the fray and hope for the best.

On Tue, 20 Dec 1994, Miles Constable at Edmn wrote:

> make, however, most people are assumming that Archaeopteryx was running and 
> catching things.

I, for one, do not assume that Archaeopteryx itself was running around 
catching things. I would assume that it's ancestors were the ones running 
and catching. Whether or not Archy was doing the same at this stage of 
development may be moot since it is (for the most part) being deemed to 
be a full fledged flier. Therefore, it probably didn't _have_ to run 
about in it's quest for food. It could get it in flight.

In point of birds 'hopping' as opposed to 'running' (sorry, I already 
deleted this text), using this modern behavior to suggest that hopping 
was the preferred mode of transport in the ancestral form seems somewhat 
presumptuous. I certainly have never seen anything that suggests 
Archaeopteryx was a hopper (of course, I have seen nothing to the 
contrary either). The fact that running starts in birds are rare does not 
discount running as an evolutionary starting point for flight.

> I suspect the basic problem would 
> be the amount of lift that could be generated by a proto-bird that lacks a 
> keeled breast bone. The muscles would be much weaker without one and would 
> not be capable of generating much lift. This, I think, is the crux of the 
> arguement and shifts it in favour for a glider as being the evolutionary 
> branch for flying birds.

I can't argue with this. However, it also doesn't discount gliding from 
ground level (run...glide...land...run...glide...land). Then generating 
lift for higher and longer glides, and from there to powered flight.

> Once into a tree the glider does not have to 
> generate a large amount of lift to get off the ground (and thus does not 
> need large muscles to do this), it just has to be able to keep it's wings 
> extended and let gravity do the rest.

But doesn't this assume that it knew how to glide first? If you kill 
yourself leaping out of trees _without_ the ability to glide, there isn't 
much evolutionary advantage in it.

>  So, in all, I think the 
> glider is the most likely scenario for the development of Avian flight.

Unfortunately, I don't see too much similarity between gliding and 
powered flight. The two modes of flight are quite different in method and 
body use (derived avian gliding notwithstanding, and even _these_ gliders 
can generate lift by flapping). All the gliding animals mentioned up 
to now (excepting avians) have _failed_ to produce powered flight (flying 
squirrels, lemurs, etc.), so how does gliding fit in to the evolution of 
powered flight? (Yes, I am on both sides of the argument when it comes to 
gliding. It _could_ have been an evolutionary step towards powered 
flight (and a mighty convenient one at that), however I fail to see how 
gliding would develop the avian style of wing where it failed to do so in 
gliding mammals. Why dont we see powered flight in squirrels?)

I don't know that the argument here is so much one of whether gliding was 
or was not a stage in the development of flight (since gliding is not 
precluded in either the cursorial or arborial schemes), but more one of 
whether _full_ powered flight (or even gliding) came on the ground or 
after a move to the trees.

In case it is difficult to tell, I am a fence-sitter with leanings toward 
the cursorial mode of origin. I havn't seen any _really_ persuasive 
arguments for an arborial origin over any other, and I just find it too 
difficult to believe that a critter climber up into the trees, jumped 
out, and THEN developed wings. It just seems more intuitive that the 
wings be there first.

Whew... Well, that wasn't so hard after all. All I can add is "be gentle 
with me...It's my first time."

Shaun Sinclair