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In answer to the query about feather shape, wich includes symmetry, considerthe
Body contour feathers have a variety of shapes (e.g., their outline form),
but they are uniformally symmetrical. That is, the shape of both sides of the
vane are essentially similar, but mirror images. The most notable asymmetric
feathers are the parimary flight feathers. This asymmetry is associated
with the ability to fly, and the primaries of Archaeopteryx are asymmetrical.
In some extant birds that have become flightless, the primaries are
no longer symmetrical. I think the asymmetry of flight feathers is a derived
Various decorative feathers in modern birds have become slightly
symmetrical as their overall shape is highly modified. There are still
considered to be contour feathers. In some cases (unpublished data) the
area of the vanes remains the same, but the outline changes.
In penguins, the contour feathers are symmetrical. However, they are
modified from those in mose birds as it appears that many of the barbs
have fused and, in effect, the surface of the feathers is shield like.
These are NOT scalses, although they have been called such in popular
books. The feathers on the wings are all higlhy modified in this direction
and mostly even lack barbs on their edge.
There are other examples of morphological modification in the barb
strucutre of feathers. For example, in speices where the feathers have a
tip (the waxy deposit on the wings of Waxwings is the best known) a similar
condition can be found.