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Re: Epidexipteryx feathers

(Posted in plain text.)

Without speculating on the possible functional role of the  elongate tail
feathers on _Epidexipteryx_, they are inherently interesting.  The authors
describe the distal portions of the 'non-ETF" (that is, the body  feathers
rather than the tail feathers) as "composed of filamentous  parallel
barbs, similar to the condition seen in the non-shafted feathers..."  Well
a "non-shafted" feather is usually referred to a down, so there  is
probably no reason to introduce a new term here. The  parallel
configuration could result from the fact that each was  produced
independently and they were preserved in registrar, or they share  a
common base, which not was preserved and the barbs ended up preserved  in
a comb-like registration. The authors observe that the "free distal  barbs
arise from the edge of a membranous structure, an arrangement that  has
never been previously reported". This is not quite accurate. In  many
tipped feather structures, for example Cedar Waxwings (Brush &  Allen,
1963); Scaled Cuckoo (Brush, 1965) and others (Brush, 1967) the barbs  are
fused to form a scale-like structure. These structures are always  distal
ward on the feather and in some cases individual barbs protrude.  the
structure is produced by the fusion of barbs along the selected  portion
of the feather and are produced by the follicle as the feather  is
produced (this means it begins early in development and then switches  to
a standard shaft/barb pattern). The facial shield on the Purple  Gallinule
and American Coot appear to be similarly constructed.  I  suspect, but
obviously cannot proved that the feathers on Epidexipteryx are  produced
by a similar mechanism.

The long ribbon-like tail feathers  may also have a precedence. In their
chapter on Birds in the "The Jehol  Fossils" Zhang and Zhou describe two
such cases. One in the well known  _Confuciusornis_ of a pair of elongate
tail feathers which have a  racquet-like structure. Similar feathers exist
in extant Motmots and  hummingbirds. The mechanism by which they are
produced is known and they are  considered to be involved in display. The
second is in the same chapter in  the reconstruction of _Protopteryx_ they
indicate the long "central tail  feather...may represent the ancestral
type of feather" (pg 144). The  implication is that a scale was somehow
reconfigured into a feather. A  similar scenario for the origin of
feathers was proposed by P. Regal (1975).  This scenario is unlikely as
avian scales develop differently and contain  different from extant
reptilian scales. The statement itself disagrees with  Zhang and Zhou's
description (pg 123) of the 'current picture of feather  evolution" which
is essentially that proposed by Prum & Brush (2002,  2003).

It seems unnecessary to coin new terms to describe the feathers  on
_Epidexipteryx_.  All the features occur in extant feathers and  are
produced by a common mechanism based on the geometry and  ontological
processes of the follicle. Fusion of parts (barbs, barbules, etc)  not
uncommon is a variety of taxa implying that it is a mechanism capable  of
producing a great deal of morphological variety. Apparently these  very
early forms were no exception.

Alan H  Brush
92 High Street
Mystic, CT. 06355
(860)  572-1717
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