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protofeathers



Tim Williams asked about "the difference between a "feather" and a
"protofeather".

I was probably as responsible as anyone for introducing the term to the
scientists who had the specimens of Sinosauropteryx. I'm not entirely
sure I can answer the questions to anyone's satisfaction as the issue, at
the time, was as political as it was scientific. 

When we first saw the specimen in Nanjing in 1997 there was a paper in
Chinese (Ji, et al) that discussed the features as hair or feathers.
There was a manuscript (Chen, P.j) in revision in Nature with the
description in English. We (Ostrom, Wellnhofer,  Martin and me) were
guests of the Chinese and were, in essence, being asked to validate the
observations made by the Chinese scientists. Most readers of this list
have at least seen images of the epidermal structures on Sinosauropteryx.
The available photos are reasonably accurate. At the time, we did not
agree among ourselves as to the nature of the filaments. Martin suggested
they might be collagen. We did agree that in our public statements, and
in a press release we prepared while in China (for the National press and
TV) that we could not unequivocally identify the structures as feathers.
That is, except for the single, unbranched filament, we could not tell if
the structure was hollow, if the filaments consisted of fibers, etc. We
knew that modern birds produced structures similar to these, as well as
many others identifiable as feathers.

We were also uncertain of the age of the specimens (although we did
collect samples that were subsequently dated). Ostrom and Wellnhofer, of
course, had no problem establishing that Sinosauropteryx was very similar
to Compsognathus. Ostrom had published on the osteology in 1978 and the
specimen is in the Bavarian State Collections which Wellnhofer curated.
But we could not say positively that the structures were feathers. And
they existed on an animal more primitive than Archaeopteryx. The thought
was that  we could not say with convection that they were not some type
of feather--or a feather precursor.  Further study was clearly required,
but Chen acknowledged our help in the published manuscript.  I spoke at
length with the group in Nanjing that had a scanning  electron scope, the
most likely facility locally to continue the studies. I don't know if
this was followed up or not.

At that moment we were uncertain. In Nanjing I was shown other specimens
that were clearly individual feathers. No question about it. I was told
they had come from the same beds. And, in fact, when we went to the fieid
site later was I handed or found similar specimens. At that instant, as
the Chinese held that the site was Late Jurassic, I realized I had more
Mesozoic feather fossils in my hand than existed in the entire western
hemisphere. That was a mind blower! Well, now we know that the specimens
are Cretaceous. And that other fossils (none as  primitive) from these
beds also have feathers. And that feathers occur in more derived
specimens.

I have since published on the role that the concept 'protofeather' has
played in our understanding feather evolution. It turns out that similar
structures are found on other  Chinese specimens. Similarly, the simplest
structure that a avian follicle would produce would by a simple, hollow,
unbranched, filament built from self-associated fibers of beta-keratin.
Superfically, very similar to the strucutres we called "protofeathers"

In the case of a "protofeather" it may be that the most primitive and the
most simple may be one-in-the-same. We may never resolve this question.
However, evidence from development, computer modelling, modern bird
epidermis, and the fossil record can be brought to bear on the issue. I
happen to know that just such studies are currently in progress.

Stand by.

Alan


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