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Re: SICB Report, part 1 (long)



Betty Cunningham, that flying goat we all saw in our dreams last
night, wrote:

<<Birds don't stick out behind at all but MANY still stick out in
front-including the early forms we DO know. What balances birds in
this? the upright S-shaped posture of the neck over the shoulder and
keel.>>

Nicholas J Pharris wrote:

<One thing I haven't seen mentioned in this thread yet is that modern
birds, unlike non-avian theropods, have (nearly) immobile femora that,
as far as I can tell, stick straight forward, effectively displacing
the "hip" joint (actually the knee) to a position under the wings.

My suspicion would be that at the same time as aerodynamic
considerations forced the shortening of the tail in the line leading
to modern birds, balance was maintained through the locking of the
femora in a forward position (effectively sacrificing a leg segment in
return for an aerodynamically suitable tail), along with  some
reorganization of the posture, as Betty suggested.>

  Avian balance as supported by the forward position of the knee was
discussed to some degree, as I recall. However, the femur of birds do
move, even in the walking phase, though the motion, if I remember the
articles correctly (somewhere in Audubon or Sci. Amer., as well as in
GSP's great book) is limited to something like 10 or less degrees
down; but in running, many birds will swing that femur downward around
45 or 60 degrees, greatly increasing the stride length (as in
ostriches) and making the body bob up and down. For that last example,
take a look at walking ratites (Jim Farlow can attest to this readily
in emus) is that the front of the body bobs up and down every time a
step is taken. Have to sit down with slowed footage to tell you the
pattern, but something's happening there that might explain part of
the balance problem.

  Anway, my 300 yen.

==
Jaime A. Headden

Qilong, the website, at:
http://members.tripod.com/~Qilong/qilong.html
---
All comments and criticisms are welcome!

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