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Sinosauropteryx fibers



> Ernesto J. Carmena <u199873203@abonados.cplus.es> wrote:
> Are the integumentary structures on _Sinosauropteryx_ branched?

According to Dr. Philip J. Curie (SVP meeting, October 10, 1997, Chicago)
and according to the _Nature_ paper by Pei-ji Chen, Zhi-ming Dong, and
Shuo-nan Zhen (Volume 391/January 8, 1998, pp. 147-152), yes, the filaments
do branch, although (due to the dense piling up of the fibers on top of one
another) "the topography of this branching is not yet clear."  Chen et al.
state:

"The morphological characteristics that we describe suggest that the
integumentary structures seem to resemble most closely the plumules of
modern birds, having relatively short quills and long, filamentous barbs. 
The absence of barbules and hooklets is uncommon in modern birds, but has
been noticed in Cretaceous specimens."

(Footnote: Grimaldi, D. & Case, G. R. A feather in amber from the upper
Cretaceous of New Jersey, _Am. Mus. Novit._ 3126, 1-6, 1995).

In Philip J. Currie's book, _Encyclopedia of Dinosaurs_ (ISBN
0-12-226810-5), he states:

"The integumentary structures were simpler than true feathers, and each
seems to be composed of a central rachis and branching barbs but lacks the
aerodynamic quality of avian feathers."

The writing of this passage predates Currie's SVP presentation, which -- if
I recall correctly -- didn't name the structures as a "rachis" and "barbs."
 But he did project a sketch of the "simple branching structure" he
observed.  It looked like a small bundle of fibers pinched together at the
base.  To my eyes, there was no organization of a distinct central rachis
and barbs, but I am basing this on my quick sketch of the projected image,
so I could be in error here.  (Photography, video and audio recording are
prohibited at the annual SVP meeting).

Again, it should be pointed out that the structures are piled together so
thickly that it has so far proven impossible to isolate individual
"protofeathers" (if that is the word for them).  Fossil bird integuments
from the same deposits are similarly densely matted, and also difficult to
study in detail.

The _Nature_ article confirms that the fibers are coarser than the fur of
mammals in the _Sinosauropteryx_ size range, and its authors concur with
Currie that the fibers may have been hollow, based on the structures being
darker along the edges (contrary to my previous post on the article wherein
I incorrectly stated that the fibers were darker medially).  Currie
projected a fiber cross-section at the SVP meeting which was he described
as looking "like a donut."  The illustration has not been published.  

I should also point out that not everyone agrees with Currie or Chen et al.
 Following Currie's talk, Larry Martin publicly conceded that thicker
structures start to divide into thinner structures (presumably referring to
the branching fibers), but objected strongly to the suggestion that the
integument might represent primitive feathers.  He felt that Currie's
donut-like fiber cross-sections appeared comparable to the structure
observed in small scales on lizards.

You will recall that when Ostrom, Wellnhofer, Martin, Brush et al. returned
from examining _Sinosauropteryx_ fossils in China, they were not able to
reach a consensus on the exact nature of the integument except to say that
they did not have the morphology of modern feathers.  On the other hand, I
would say that the "subdermal collagen fibers supporting a structure
comparable to a sea snake tail in _Sinosauropteryx_" hypothesis proposed by
Geist, Jones, and Ruben at the 1997 SVP meeting was soundly refuted by
Philip J. Currie's observations at the meeting.  (Further details are in
the archives).

We can look forward to further study and descriptions of 
_Sinosauropteryx_, as well as research on _Protarchaeopteryx_, _Mononykus_,
and other yet undiscovered and undescribed theropods with fossilized
integumentary structures.  It's an exciting time for paleontology, if only
we can take the suspense...

Ralph Miller III <gbabcock@best.com>