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Along others, I was invited to the
National Geographic last Wednesday (19.I.00)to examine the specimens on display
and which were the subject of the article last November. The display was being
dismantled and we were given free access to all specimens, enjoyed continuous
among those present and were welcomed by Geographic staff. What follows are some
of my observations and thought.
The specimens on display were
Sinornithosaurs, Archaeoraptor, and Beipaosaurus. In addition there were the
standard graphics associated with such a public display which included various
diagrams and quotes from the printed article. There were a number of
reconstructions of the Chinese material along one wall. There were executed by
various artists and, in my mind, represent art not science. I will not made any
judgements or even venture an opinion regarding these.
All of the specimens had the filoform
structures observed on so many of the Liaoning material. In one case,
Beipaosaurus, there were areas where the material was so dense and so well
preserved, that entire isolated filaments have been preserved. On all 3, the
material is general present as impressions, albeit very well defined and clear.
The rest of Beipaosaurus is equally well preserved and prepared.
None on the specimens have recognizable
feathers as found on Caudipteryx, Protarchaeopteryx and Archaeopteryx. Lacking
more evidence, the filaments fall into the category of protofeatthers. Calling
these specimens 'feathered dinosaurs is speculative at this time. It may turn
out that these structures are a feather precursor or a primitive feather.
However, they may proved to be something completely different. In my opinion
they are very likely epidermal in origin, unbranched, and structurally quite
rigorous. They certainly covered a large portion of the body surface. The fact
that one cannot unequivocally identify these structures does not lessen the
value of the specimens.
The thrust of the National Geographic
article (Feathers for T. rex?) in some ways reflects the confusion
dealing with the terminology regarding protofeather, primitive feather, and
feather. The structures on the Chinese material beginning with
Sinosauropteryx was been used rather loosely, including the origin
references to 'hair-like'. Hair occurs only on mammals. Filamentous structures
(that may be described as hair-like or bristles-also found on brushes!) occur on
insects, plants etc. They are filaments in forms but all composed of very
different material and produced in different ways. So the filaments on these
specimens may turn out to be keratin-based and produced by a follicle, but until
we can prove that, we cannot, strictly, call they feathers. Nor can we say where
in the evolutionary history of feathers they played a role (if they did). One
must be very careful here an not confuse convergence on a simple shape (i.e.
hair-like) with a precisely characterized feature (feathers) of a group of
animals (e.g. Birds).
If the information on the internal
anatomy, molecular composition, and ontogeny were available the exact nature of
the structure could be established. But the 'hair' of insects consists of solid
rods and is made from polysaccharides (not proteins). And the hairs on plants
are, except for their shape and presence on the surface, made from yet another
set of chemicals.
The slab with the Archaeoraptor is
relatively poorly preserved compared with the other Liaoning material. Like
other specimens there are filaments present and on one area a series of
semi-isolated tufts. I have not seen anything exactly like this previously, but
it might simply be an artifact. While the quality of the preservations of the
filaments varies within and among specimens they all have the structures and in
similar geometry to the body surfaces, and it is widely
distributed.
I would like to point out once again
that the concept of a protofeather is a human concept. It is a hypothetical
construct. It is my fondest wish that some day the hypothesis will be disproved.
A primitive feather is another matter. We will eventually be able to establish
which, among the many feather types, was primitive (I have some ideas on this,
but that is another story). Hopefully, there will be a beast attached to it.
However, even the oldest known feather bearing animal (Archaeopteryx) has more
than one type of feather. Conceptually, a protofeather would have been the
earliest feather, but we have no information now as to where these concepts
converge either in time or 'morphological space'.
Alan H.
Brush
M.J. Spring Brush 92 High St. Mystic, CT 06355 brush@uconn.cted.edu
860-572-1717 |