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Archaeopteryx Propatagium



A new paper has been brought to my attention (lessee if I bungle this one).

  Martin, L. D. and Lim J.-D. 2005. Soft body impression of the hand in
*Archaeopteryx*. _Current Science_ 89(7):1089-1090.

  No need for a dense, investigative study, this is the entire main text:

  "While studying the wing feathers of the famous Berlin *Archaeopteryx*, we
noticed that the hand and arm are surrounded by a natural depression.
Impressions of the calamus of various feathers extend into this depression,
indicating that it formed before the decay and loss of at least some of the
associated soft anatomy surrounding the skeleton. The lithographic limestone
normally shows little surface relief and few alternative explanations are
available for depressions along an articulated and largely undisturbed
skeleton. We wondered if this really was a soft tissue impression and whether
we could recover a cast that would help us understand the hand in the oldest
known bird. Our attempt (Figure 1) revealed an essentially avian hand with the
outer and middle fingers united nearly to the claw and a long posterior
patagium extending along the margin of the hand and arm. Heilmann1 postulated a
similar structure probably because the deep follicles that anchor long primary
feathers require this morphology. We think that the middle and outer fingers
were also united in other forms with long primary feathers (*Microraptor*,
*Caudipteryx*)2,3, although they, *Archaeopteryx* and *Confusciusornis* are
routinely restored with separated fingers2-4.

  "There are also indications of an avian prepatagium (Figure 2). The presence
of a prepatagium constrains the extension of the forearm so that the junction
between the humerus and the radius and ulna usually reflects the pattern of
avian wingfolding in bird fossils. It is significant that all of the fossil
skeletons of *Archaeopteryx* preserve an avian folding pattern on at least one
wing. We conclude that the soft structure of the *Archaeopteryx* wing, like the
feathers5, was essentially modern in conformation. Such a hand lacks
significant grasping capabilities and was of little use for capturing the small
prey, indicated by the size and shape of the teeth and mouth. We suppose that
the fingers and claws were used primarily for climbing6. The primary feathers
at the tip of the wing would have run under the outer finger to attach to the
middle finger. The outer finger was probably above the middle and free for a
short distance. This may explain why the outer finger crosses the middle finger
in the preserved specimens. In more advanced birds, the outer finger is greatly
reduced.

  "1. Heilmann, G., The Origin of Birds, Witherby Press, London, 1926.
   2. Ji, Q. et al., Nature, 1998, 393, 753?761.
   3. Xu, X. et al., Nature, 2003, 421, 335?340.
   4. Padian, K. and Chiappe, L. M., Sci. Am., 1998, 278, 38?47.
   5. Martin, L. and Czerkas, S., Am. Zool., 2000, 40, 687?694.
   6. Feduccia, A., Science, 1993, 259, 790?793.
   7. Lucas, A. and Stettenheim, L., Avian Anatomy Integument (Part 1), 
      Agricultural Handbook 362, US Printing Office, Washington, 1972."

  Martin and Lim are-- Oh, wait, better comments first. I find it amazing this
was tested on CASTS, special or no, and that the entire text boils down to two
paragraphs, little of which was spent on providing a context for preserving the
integument they cite exists. But I must say, we are spared the Feduccia
soundbytes, for the most part, and the anti-Birds are Dinosaurs camp
commentary. Martin, at least, is a bit more worldly than Feduccia, grounded in
more practical sciences and the study of wonderful critters like sabretooth
kitties (mrowr); I think on the whole he's a good guy, but enough gushing. They
seem to ignore that others have already argued about the nature of the crossed
fingers in Archie, including Greg Paul and Peter Wellnhofer, and it's bearing
on the taphonomy of the Solnhofen limestone environment, but, alas, no comment,
as if theirs were new. But I am sure they are kept up on all the latest
*Archaeopteryx* research, right? Apparently they didn't even cite
Wellnhofer.... Hmmm. Onto the harsher comments:

  The margin they see is formed by a crack in the matrix of an overlying layer
exposing a lighter layer of limestone. The overlying layer was flaked off and
the rest of the marks are tooling traces, something you can see on the other
side of the same specimen as well. This was done to find margins for all bones,
and in fact the process more often destroyed integumental impressions than
revealed them, as the case of the "lost" leg feathers attests. Notice for those
with images of the specimen that the the arm projecting away from the head has
oblique tooling matching tooling "below" the neck and underneath the arm
projecting in the same direction as the head, running in the same direction and
matching the traces in the region of the "propatagium". Thus, Martin and Lim
were wise not to push this into _Nature_, but it is likely they will still be
called on this tripe anyway. 

  However, in the end I must agree with them, especially in regards to the
nature of the arm posture, that the wing folding system would require a flexing
tendon structure internal to the elbow joint, causing collapse of the forelimb
during flexion at the wrist and adduction of the humerus and that contra
restorations by others like Greg Paul, the arm would not look like a
muscle-pared, non-patagiated version of a bird's arm, but will have a set of
tendon supported tissues to evidence the arm-folding mechanism. Yet, I think
that Martin and Lim haven't found it, using tooling traces of a single Archie
specimen in their study, and moreover that examined over a cast (though
admittedly they looked at the original first, but apparently not closely
enough). Perhaps if they study the type for traces of a skin structure (like,
non-tooled feathers, or compare in other specimens), maybe they'll be supported
in this "discovery."

  Thanks to Brad McFeeters for telling me where this is. BTW, it can be
downloaded at: http://www.ias.ac.in/currsci/oct102005/1089.pdf Enjoy.

  Cheers,

Jaime A. Headden

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


        
                
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