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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."