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

Re: Archaeopteryx and Flight and back again

> 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 can't get past the idea that from running, leaping/gliding would be an
energy loss - at least for motion.  Running animals tend to stay on the ground
so that their legs can pump energy into their motion.  

> > 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.

Why would an animal do this?  The animals that do (I believe) either have the
ability to fly or had that ability.  The discussion is (was) about animals
that will develop flight but hadn't in their past.  
> > 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.

Who said they must die?  Squirrels leap from limb to limb.  Some have developed
the ability to glide, thus extending their range.  To me, this seems a logical
precursor to flight.  

> >  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?)

Slow down here, this doesn't logically follow.  Remember that the discussion 
is about animals that haven't developed flight.  The question should be whether
they will - if permitted.  Bad arguements really get to me - intended or not...

<Stuff deleted>

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

Gentle??? HAH!  A poor defenseless victim for spoils!!! ;-)!

> Shaun Sinclair
>       ssinclai@gpu.srv.ualberta.ca

Randy King
experienced novice.