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FW: flapping from gliding



From:   Nick Longrich[SMTP:longrich@phoenix.Princeton.EDU]
....
>       The big mystery is insects. There aren't many insects today
>that give a clue to how flight may have evolved- perhaps this is because
>the overwhelming majority of them today already are winged, so they don't
>really need to evolve winglike structures. 

An article last year in Nature or Science (sorry - I don't have the reference
handy) suggests that insect wings might have evolved as means of propulsion
for insects that float on water or perch on the surface film, such as water
gliders, water boatmen etc.  

Initially they postulated using modified appendages as oars (i.e. pushing
against water), then later on wings could have been flapped in air, but not
to become truly airborne - they would push on air to provide motive force for
skimming along the surface (like those airboats they use in swamps).   Water
is key here because it is a low friction medium on which legs would not be of
much use.

Apparently  there are some aquatic insects with partial wings that actually
do this.  They can also be explained as being like the chicken - i.e. a case
of losing full wings after the fact.  However, the paper also presented
experimental evidence.  They took flying insects able to float or perch on
the surface film, and partially cut off their wings.   They were still able
to get around quite handily on the surface (but could not take off) with even
a fraction of the wing remaining.   

Mutilating insects is not proof that this is how it evolved of course, but it
is a graphic demonstation that sometimes half a wing can be useful. Truth
aside it is interesting that a plausible story can be invented to get powered
flight WITHOUT a prior gliding stage.

Although it seems pretty unlikely to me, one could postulate something like
this for birds - i.e. aquatic protobirds which would float on the surface and
flap partial wings to move quickly on the surface (like waterfowl in the
takeoff phase) without ever really flying 

Nathan