[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Feather evolution (Feduccia 1985)



        More food for thought... 
       Again revisting prior questions brought up during the interminable
bird origins deabtes.  My roommate, bless his heart, dug up _The Beginnings
of Birds_, the aforereferenced papers of the 1984 Eichstat conference.  On
of the papers in this volume is by Alan Feduccia, and concerns the origin of
feathers.
        Feduccia, A. 1985: On Why the Dinosaur lacked Feathers, in _The 
        Beginnings of Birds_ (Bronner and Drentler, Eichstatt, 1985)

        Feduccia states that contour feathers are very similar to flight
feathers.  He says, referencing Parkes, 1966, that they are practically
"mineature flight feathers".  He continues, "If feathers had evoloved
initially as thermoregulatory structures, then the body or contour feathers
[of flighted birds] should be essentially similar to the origional
feather..."  He highlights the "hairlike" degenerate feathers of flightless
birds, attemting to show that feathers which "have value only in a
thermoregulatory context" do not require all of the specializations seen in
contour and flight feathers.  Feduccia quotes Lowe 1928, discussing the
unaerodynamic properties of contour feathers, as their discontinuity causes
a "loss of resistance leading to an inability to fly."
        Feduccia does not appear to be aware of the concept of selection
pressure.  It seems clear to me that the contour feathers of flightless
birds are experiencing strong selection pressure to retain their aerodynamic
form (metaphorically speaking, of course).  The high selective advantage of
this aerodynamic form may be gleaned from the Lowe quote.  Once a bird
lineage becomes flightless, these pressures are no longer applied, and the
feathers may degenerate to whatever state will still perform the
thermoregulatory/insulative function.
        Can anyone think of a selective advantage whihc might be gleaned
from reducing the feathers.
        Feduccia's declaration that contour feathers must represent the
primitive state of feathers used for thermoregulation is of doubtful
validity.  The selective pressure which causes aerodynamic shape in feathers
need not have been present in an insulatory structure, as Feduccia points
out.  These early feathers may have existed merely as "hairlike" structures,
later developing the structure we now see in flighted birds, as a result of
the selection pressure which currently keeps them aerodynamic.  That the
contour feathers may resemble the flight feathers so closely may be due to
convergence, or the pressures on all aerodynamic feathers may be similar
enough that a common solution was reached for all.  Or the similarity could
be the result of exadaptation [sic?] of feathers from some former use (such
as shade from sunlight, or display).
        I find it astonishing that a complete counter argument can be made
merely from the evidence that the arguer presents, and a knowledge of the
basics of evolution.

        (Refs for papers cited by Feduccia available on request.  I do not
list them, as the relevant material is quoted)
        
Wagner

+--------------------------------------------------------------------------+
| Jonathan R. Wagner                    "You can clade if you want to,     |
| Department of Geosciences              You can leave your friends behind |
| Texas Tech University                  Because your friends don't clade  |
| Lubbock, TX 79409                               and if they don't clade, |
|       *** wagner@ttu.edu ***           Then they're no friends of mine." |
|           Web Page:  http://faraday.clas.virginia.edu/~jrw6f             |
+--------------------------------------------------------------------------+