Re: four winged Archaeopteryx

["Jaime A. Headden" <qilongia@yahoo.com>]

Greg Paul (GSP1954@aol.com) wrote:

<The humerus has a greater diameter than the femur, and the radius and ulna are
more robust than the tibia and fibula. If the arms of Archaeopteryx were for
display or turning etc while running then the arms should not have been as
strongly built as the running legs. That the opposite is true indicates the
arms bore the primary load in some form of locomotion. Climbing is a partial
explanation, but only in flight would the arms bear almost or all of the load.
Add the enormous wings (same wingarea & span/mass ratios as in standard birds),
very large arm muscles much bigger than in normal theropods, and so forth and
you have something that is beyond passive gliding and into some crude form of
powered flight. As for the tail feathers well peacocks fly.>

  As Greg has stated before here and in print, "flight-related" features can
exist in the absence of flight, and indeed, pre-adapted features can be further
adapted into a different functional complex. Thus it is possible to have robust
humeral diameter but not be able to lift the humeri above horizontal. The
evidence linking the two is anecdotal, not practical, as no 3D undistorted
Archie fossils exist for us to eliminate estimates by sight, as has been done
so far.

  There also seems to be a small rule of thumb, though I have not spent much
time testing this but the time I have had to do so bears this out to date:
Scapulae with expanded distal ends typically do not lie dorsal or even closely
appresed to the rib cage, but lie above it and often more to the side than to
the top, such that the scapula is given freedom of movement to move somewhat
(or muchly) forwards and back. This appears to be the anatomical case in the
Thermopolis *Archaeopteryx*, though the distal scapulae in most other specimens
is much more difficult to ascertain as it is imperfectly preserved in nearly
all other specimens with the element. Those that show the distal end appear to
be broken at this, and the "taper" in some is clearly indicative of fracture if
we assume the condition in the Thermopolis specimen to be natural. Thus it
would seem to be that scapular motion lateral to the spine was possible in
*Archaeopteryx*, or at least that specimen, and this belies the placement of
the scapula dorsal to the ribcage and in fact in any position directly similar
to that of extant volant birds (and many non-volant ones).

  Thus I diagree with Paul's premise regarding *Archaeopteryx* humeral mobility
based on anything such as scapular position. My opinions on this matter
coincide with Senter's and Cowen's.
 
<When I manipulated the humerus of Coelophysis rhodesensis in the laterally 
facing glenoid of a cast many years ago I had no trouble getting it to go way
above horizontal, diagram in PDW; same with Deinonychus (this is not doable in
all theropods). In Archaeopteryx the glenoid faces at least as laterally.>

  Practical experiments of this nature aside, it should be noted that cartilage
and scapular position on the ribcage must be taken into account. This is not as
easy as it looks, as most *Coelophysis* ribs and scapulae are broken and
reconstructed (especially the Ghost Ranch specimens) and deposition in a
fluviatile mudflow makes natural and perfection preservation nearly impossible
to expect.

  However, although *C. rhodesiensis* is very likely distinct from *C. bauri*
in some details, in this regard, the ventrally facing glenoid in both specimens
should caution the method of restoration or eversion of the humeral caput and
articulation of the proximal humeral trochanters (dorsal and ventral processes
in birds). Placing the scapulocoracoids into an avian position, even assuming
an avian sternum, causes problems with the orientation of the scapulae, as in
facing the lateral surface of the coracoid cranially, naturally everting the
scapulae and rotating them dorsally and medially, resulting in a primarily
laterally facing glenoid. This is the onyl possibility that I can see in
producing a humerus that can raise above the horizontal when everted laterally,
based on my observations of coelophysid scapulocoracoids (although I admit less
familiarity than Greg, Phil, or indeed many others in this regard).

  Cheers,

Jaime A. Headden
http://bitestuff.blogspot.com/

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

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