Natural Science Forum / Biology / Paleontology / July 2007

It was probably in a transitionary stage or even like dolphins and
whales was evolving limbs from wings which evolved from limbs. The
gilding part of you post makes me think something like that.

Flight is the process by which an object achieves sustained movement
either through the air by aerodynamically generating lift or
aerostatically using buoyancy, or movement beyond earth's atmosphere,
in the case of spaceflight.

http://en.wikipedia.org/wiki/Flight

A wing is a surface used to produce lift and therefore flight, for
travel in the air or another gaseous medium. The wing shape is usually
an airfoil. The first use of the word was for the foremost limbs of
birds, but has been extended to include the wings of insects, bats and
pterosaurs and also man-made devices.

A wing is a device for generating lift. Its aerodynamic quality,
expressed as a Lift-to-drag ratio, can be up to 60 on some gliders.
This means that a significantly smaller thrust force can be applied to
propel the wing through the air in order to obtain a specified lift.

http://en.wikipedia.org/wiki/Wing

The Evolution Of Flight

Perhaps the most perplexing and controversial aspect of the study of
flight is the study of how and why flight evolved. Since flight
evolved millions of years ago in all of the groups that are capable of
flight today, we can't observe the changes in behavior and much of the
morphology that the evolution of flight involves. We do have the
fossil record, though, and it is fairly good for the three main groups
that evolved true flight.

...The most amazing fact about the evolution of flight is the extent
of convergent evolution between the three main groups that evolved it
(again, the pterosaurs, birds, and bats). In this convergence, we can
see some semblance of general "rules" that may govern how animals
evolve flight, and from these rules we can perhaps glean a hint of
what it takes for an animal to have potential for flight.

Flight Origins: How and Why?

...Evolution is limited by developmental and genetic constraints. If
an adaptation is useful to a lineage, chances are that it will be
preserved. If an adaptation is co-opted from a previous use to a new
use, it is called an exaptation. The only scientific way to approach
why flight evolved in a group is to first figure out how it evolved;
what the temporal sequence of exaptations and adaptations was.

...If our study of functional morphology determines that the ancestor
of a flying group must have been a glider, and we think that it was
arboreal (like all modern non-aquatic gliders) then flight must have
evolved from an arboreal gliding ancestor. If we have fossilized
tracks of our probable ancestor, then we can tell how it was moving on
the ground. If we figure out that the probable ancestor of a flying
group was a bipedal cursorial (running) form, then flight likely
evolved from the ground up.

How and Why Did Wings Evolve?

...Scientists generally agree that wings must have been exaptations;
they were used by the ancestor for one function, and became useful for
flight among the descendants (if they weren't exaptations, then they
were adaptations, which would mean that they were wings already used
for powered flight; a circular argument).

A comparative study of the functional morphology of the wings of the
earliest known flying members of the lineage with the "pre-wing"
structures of likely ancestors and close relatives provides the best
evidence for how wings evolved.

1. Wings evolved from arms used
to capture small prey.

2. Wings evolved because bipedal animals were
leaping into the air; large wings assisted leaping.
This is possible; any amount of wing could assist
leaping. ...we first need phylogenetic evidence for a
bipedal running or leaping origin.

3. Wings were used as sexual display structures;
bigger wings were preferred by potential mates.

4. Wings evolved from gliding ancestors who
began to flap their gliding structures in order
to produce thrust.

It seems that #1, #2, and #4 are the best hypotheses to use for the
origin of wings because they can be tested by bringing in other lines
of evidence. Move on to consider these origins, but remember: the
issues of the evolution of flight and the origins of flight are
inextricably linked.

Summarized From;
http://www.ucmp.berkeley.edu/vertebrates/flight/evolve.html

http://www.grc.nasa.gov/WWW/K-12/airplane/short.html

So let's see. The mature common crow's wingspan is 30- 40cm. If we multiply
that by 1,000, we get something like 30,000 cm. This would be the rough
equivalent (someone check my math) of 0.3 kilometers, 12,000 inches, 1,000
feet, or (for you sports fans) just less than three football fields or the
length of a Nimitz class aircraft carrier.

Somehow, I get the sneaky suspicion that this bird is a physical
impossibility, likely dreamed up by either a scientologist or a creationist
or someone with a bit too much crank up his snout.

     I have difficulty visualizing this animal. Does it look like a
piece of string? White string?