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Re: really big question



Cliff Green (dinonaut@emerytelcom.net) wrote:

<OK. Many professionally rendered Ostrich Mimic dinosaurs in the past
decade have been portrayed as being feathered also. I am assuming that
this is due to Ostrich mimics supposedly being cladestically close to
dromeaosaurs. Or are they?

I recently came across this while doing research for a potential
commission. Pelecanomimis Polyodon, ( pelican mimic with many teeth ) a
small two meter ornithomimid, was found in Spain just over ten years ago.
It has amazing muscle and internal organ preservation. It also has great
skin impressions with not only zero plumage, but no scales as well. It has
smooth skin with a dewlap and a occipital crest on the back of it's head.
It also has a keritaneous beak with a mouth full of 200 small teeth. It is
considered to be a primitive form.>

  Though I understand Mickey Mortimer's position regarding the implication
that the polygonal imbrication of the tissue represents surface skin
texture, there is no positive identification that this would be true of
its skin condition for a variety of reasons, not the least being the
manner of preservation.

  1. Lagerstätten seldom preserve impressions of any sort, especially
typical limestone quarries; rather, sandstone/ash lagerstätten (incl. Las
Hoyas, Sihetun, Jianshangou, etc.) preserve the carbonaceous remains of
skin, or of the ossicles within the skin itself. Note the raches and barbs
of the feathers themselves are preserved as collapsed structures, but not
as impressions ...

  2. ... leading to the nature that collagen and keratin itself will form
the carbonaceous remains, as in some remains of *Shuvuuia,* ichthyosaurs,
the various "dino-birds," and so forth. Skin impressions, when apparently
present, appear to be related to the preservation of scales themselves, as
in the feet of specimen NGMC 91 of *Sinornithosaurus* ("Dave"), or in the
tail of *Scansoriopteryx* (scaley, imbricating pattern), rather than in
the nature of the impressions of skin, etc.

  These would imply that lagerstätten wouldn't preserve skin features, and
collagen and keratin from the skin, as in ichthyosaur preservation, or the
aktinofibrils and "fur" of pterosaurs, is the only thing preserved. As in
the ichthyosaurs, this has LITTLE to do with the nature of the surface of
the skin, and false patterns arise due to layering of multiple levels of
collagen.

  This would be a clear alternate explanation for why "feathers" are not
present on *Pelecanimimus,* and why the material, including the striated
"gular pouch" and the "fez" on the back of the head, are not evidence for
naked skin, but the underlying material. It is not determinable, based on
the collagen/keratin evidence known, to determine the nature of the
surface of skin, though it's possible, as with birds today, that the head
was likely bare of scales, may have been "feathered" -- or, indeed, the
head may truly have been scaled.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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