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Re: Still more Archaeopteryx
On Thu, 22 Dec 1994, Constable,Miles [Edm] wrote:
> Ah Shaun, you stepped right into it. What comes first? The structure or the
> ability? Evolutionary biologists have argued this for ages.
Aha...The old 'chicken-or-the-egg' trick. :-)
> As Steven
> Jay Gould points out, evolution may not be all that incremental, it may
> stagnate for long periods of time interspersed with large leaps of
> development. However, Archaeopteryx may well be a very good example of an
> incremental development that may have lead to flight, or may not have.
I certainly agree with him on this--Although I would probably add that
both processes take place in nature (although any process can be
described as punctuated depending on the resolution used to view it).
> As others
> have pointed out, birds that run a lot ie. roadrunners, keep their wings in
> to avoid drag. They don't flap or glide to catch prey. So, it is at least
> likely that Archaeopteryx did not do this either.
Hmmm, as one who has lived out in the boonies and has had to chase down
chickens (and ducks, geese, turkeys), I can state with certainty that they
_do_ use their wings to perform quick evasive maneuvers and to get lift
to escape lunges. And they are quite effective at it too. THey can also
be formidable weapons (at least the geese/turky sized ones), and
help to suspend the body in the air so that the spurs can come into play.
Whether wings evolved _because_ of this is questionable, however once
these structures began to appear, they most certainly would have been
used to perform similar stunts (and may have had stronger selection
pressure as a result).
It is true that the ground living birds keep their wings tucked, however,
so do all the tree dwelling ones (excepting for flight/balance of course
[Ooh, I bet I get flamed for that over-generalization]). I cannot see the
having your flight feathers hanging off of your forearm while you are
climbing a tree trunk (or through the branches for that matter). There
would be too many chances to damage them on
branches and the like. I would think that a tree dwelling animal would
evolve a more compact, close-to-the-body system than long feathers
hanging off the forearm.
> I don't buy the argument that because "flying" squirrels did not develop
> flight from gliding then birds did not either.
Woah there, I hope that that is not how I came off sounding. I would
_never_ make a statement like 'because not this then not this either' (at
least not intentionally). The possibility is _always_ there that almost
anything can happen given enough time. There is the possibility that
bird-flight DID evolve out of gliding flight. That being said, other
methods cannot be discounted either. Without a modern analogue for
glider->powered flight, and given the fact that of all the modern gliding
tree dwellers not one has attained powered flight (and have in fact
remained remarkably stable for quite a while), I find it harder to
believe that this one organism switched instead of sticking with what
appears to be a very stable end product. If gliding from trees was just a
convenient way of attaining powered flight, I would suspect that other
organisms would have attained it as well. Given the difficulty in
switching from gliding to powered flight (ie. the complex body changes
required), the urge is to look for a simpler method utilizing smaller,
more gradual changes incorporating body movements and functions that had
the potential to develop into 'flight-like' motions. These
movements/functions would have had to have _some_ purpose. Therefore
heat-regulation devices (feathers) being used in pursuit/escape seems to
be a reasonable alternative with no large leaps involved (pun intended
Neil Clark said:
> I've said enough now. Please be careful over the Holidays and don't
> try jumping out of trees. It is unlikely that your particular morph is
> developed enough for flight.
> Best wishes for the new year...
After spending much time in my formative years doing just that, I can
attest to the truth in that statement. ;-)
Merry Christmas to all,