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RE: flight



Phillip Bigelow writes,

> If you happened to watch Larry Martin describe his Archaeopteryx on the
>1990 Nova telecast, there are some things to note about Martin's
>reconstruction ("The Case of the Flying Dinosaur").
>  Martin has his Archaeopteryx in a near primate-like stance.  According to
>Martin, this would give the protobird a center of gravity closer to the tree
>trunk, and would facilitate climbing.   However, if you look closely at the
>tail vertebrae on his mount, Martin has the tail curling backward and
>upward.  I am just guessing here, but I presume that the tail orientation is
>"artistic license" on Martin's part.

Hmm, I have not seen the reconstruction, but the curling tail rings false
to me. If you take a look at the most complete specimen of _Archaeopteryx_,
the Berlin Specimen, the head is twisted and curled backwards to such a
degree that the top of the skull is almost pointing to the backbone of the
animal.  This is the typical 'agony' position which is caused by the
shrinkage of the major tendons and ligaments which control neck movement.
The tail, in contrast, is straight - in fact it is slightly curved
*downward* i.e. like a "(" on its side but with less curvature.  This
indicates that there was no major tendons or ligaments associated with the
tail and thus it is unlikely that the tail could curve very much at all,
let alone curve upwards.  It is, however, articulated at a curious angle to
the backbone.  This may be an artifact of preservation, or it may indicate
that the tail could be moved upward and downward from the junction with the
backbone (you can get some idea of what it looks like if you hold your hand
out, palm up and curl all the fingers and thumb - except the index finger -
into the palm.  Now, whilst keeping the index finger straight, bend the
finger at the joint with the hand.  This motion - the straight finger is
the tail and the finger/hand joint is the tail/backbone joint - may in fact
be a method of keeping the tail out of the way).  This situation also
occurs in the London and Eichstatt specimens.  So instead of curling the
tail upwards _Archaeopteryx_ may have held the rigid tail up, something
like a peacock - hmm, who knows, even for dispay purposed as well?  It
would certainly be advantageous if a mechanism for keeping the tail out of
the way also increased your chances of reproducing.  However, the largest
specimen, the Solnhofen specimen, is different.  Here the tail is curved so
much that is lies sub parallel to the backbone.  The curvature occurs in
the first few vertebrae of the tail only, the remainer of the vertebrae are
straight.  Also the skull is the most twisted and curved of all the
specimens, with the skull lying on some of the vertebrae and ribs.  This
specimen appears to be the most affected by post-mortem processes and this
may account for the curvature of the tail.  Since movement of the tail up
and down would require ligaments and tendons operating on the first few
vertebrae only, extended shrinkage of these ligaments may have caused
intense curvature at this point whilst leaving the rest of the tail
unaffected except for overall position.  Thus the lack of curvature of the
tail in other specimens, despite extreme curvature of the neck, seems to
indicate that the tail acted as a rigid unit rather than a flexable one
needed to allow curvature.

Chris

cnedin@geology.adelaide.edu.au,   nedin@ediacara.org
-------------------------------------------------------------------
Many say it was a mistake to come down from the trees, some say
the move out of the oceans was a bad idea. Me, I say the stiffening
of the notochord in the Cambrian was where it all went wrong,
it was all downhill from there.