Re: Integumentary blues

["Ralph W. Miller III" <gbabcock@best.com>]

So far as I know, there is as yet no consensus on the precise morphology or 
homology of the _Sinosauropteryx_ integumentary structures.  Perhaps more 
intensive study of known and future specimens will help to
confirm the hypothesis that these structures are primitive feathers, and the 
proper name will follow suit.  Ranging in length from 5.5 mm to 40 mm in 
length, the relatively coarse integumentary fibers are
thought to be hollow and may or may not branch from very short quills.  They 
are densely arranged over some areas of the specimens, gently curving and 
criss-crossing atop one another, making it impossible to
isolate individual structures for proper morphological study.  These were 
clearly external structures, and covered much of the theropod body.

Different authors have approached the terminology in different ways.  In a 1997 
paper, and, I presume, in their original 1996 description,  Ji Qiang and Ji 
Shuan referred to the integumentary structures as
"feathers," and this led to their placing _Sinosauropteryx prima_ among the 
birds, based on the notion that feathers are a diagnostic feature exclusive to 
avians.  Needless to say, this use of the terms
"feathers" and "birds" is not generally accepted, in spite of the precedence, 
and has been abandoned by subsequent paleontologists writing on the subject.

These features have also been described as "integumentary structures," 
"filaments," "fibers," and  -- usually more tentatively -- "protofeathers."  
What you call them at this point apparently depends on your
interpretation of their morphology and homology.  The conservative approach 
would be to call them "fibers" or "filaments," or "integumentary filaments."  I 
suppose you could call them bristles, too, but this
term would not be appropriate if the proposed branching morphology should turn 
out to be correct.  Unfortunately, the preceding terms are not easily applied 
as adjectives, so I can't think of a handy
replacement for the phrase "feathered dinosaur."  It is certainly possible that 
this term, "feathered dinosaur," will turn out to be proper for 
_Sinosauropteryx prima_, and I'm fond of it myself, but I think
that some paleontologists would prefer to take a "wait and see" approach before 
accepting the term.

Of course, _Caudipteryx_ and _Protarchaeopteryx_ can wear the "feathered 
dinosaur" label with pride.  Then again, so can all the birds!

Questions:
If alvarezsaurs sported simple unbranching bristles, and were indeed primitive 
birds, should their bristles be referred to as feathers?

And if (I did say "if") _Sinosauropteryx_' filaments test positive for feather 
keratin chemistry, should we then call these integumentary structures 
"protofeathers" or "feathers," regardless of whether the
filaments branch?
--
Ralph W. Miller III  <gbabcock@best.com>

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