MORE ON SCAPULAR ROTATION

[GSP1954@aol.com]

Some additional comments on the ongoing discussion on scapular rotation in
dinosaurs. 

Contrary to one recent suggestion, I have never made the absurd claim that an
animal with forelimbs shorter than the hindlimbs will "dive into the ground"
or "spin around" if it tries to run without scapular rotation to make up for
the difference. Others have, but not moi. A number of running animals have
very different fore versus hind limb lengths. Some lizards with very short
arms can trot. The hindlegs of hyenas are much shorter than the fore, but the
former do not drag along the ground. The off the ground phase of the shorter
limbs are 


simply longer than those of the longer limb. That this is considered a
problem is silly. 

Nor are size or speed speed critical factors for scapular rotation. Despite
the fact that their arms carry more mass than the legs, and they cannot run,
the scapula of elephants is mobile rather than fixed firmly to the chest. You
can see the tops of the blades moving relative to the top of the shoulder if
you watch elephants at the zoo. The shoulder joint fore-aft movement is
substantial. See the classic Muybridge series of the elephant, and P
Gambaryan (1974) How Mammals Run. The scapulas of sauropods appears about as
mobile as those of stegosaurs, ceratopsians and hadrosaurs. 

No one has ever shown why the scapula-coracoid of most quadrupedal dinosaurs
could not glide fore-and-aft in the groove of the cartilagenous sternum,
which is rarely partly ossifed and preserved (Norman, 1980). The lack of a
clavicle-interclavicle brace is positive evidence that the shoulder blade was
mobile. 

GSPaul