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Further comments on the evolution of feathers:
1. It is necessary to separate the evolution of feathers from the current
discussion of the evolution of avian flight. While flight is ultimately depend
ent on feathers, the forces that lead to the appearance of feathrs certainly pr
edate flight. Regardless of the capacities of flight in Archaeopteryx, its
feathers are in every way compatable with modern flighted birds.
2. The current discussion (Nature 370:514, 1994) on asymmetry is not yet
concluded. I have evidence based on the variation of shape that the primary
feathers in Archaeopteryx are similar to those in flighted birds. The nature
of the asymmetry depends on the location of the individual feathers in the
sequence along the wing, and with the design of the feathers. But symmetry
any asymmetry can be distinguished, and the degree of asymmetry measured.
I also have data on symmetrical feathers that differ in size and on those
whose overall shape changes but are not asymmetrical.
3. The evolutionary origin of feathers is still debated. There is
now extensive evidence from development, organization & sequence of the
keratin genes, molecular structure and sequence of the feather proteins,
biochemistry and 3-dimensional structure that feathers (including adult down,
natal down, most scales, and claws) did not evolve firectly from reptile
scales (see Avain Biology IX:121-163, 1993), but is likely an evolutionary
novelity (J. Evol. Biol., in press).
Alan Brush e-mail Brush@uconnvm.uconn.edu
Physiology & Neurobiololgy fax 203-486-3033
University of Connecticut