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Dear list members,
I read Carrier and Farmer's paper "he
Integration of Ventilation and Locomotion in Archosaurs" (appeared in
American Zoologist) with great interest. However, reading the paper also
provoced some questions in my mind.
In their paper, the authors state that
when a dinosaur stepped on the ground, its tail and torso bent downwards. This
caused the angle between the pubes and the spinal cord to decrease, decreasing
abdominal volume. The abdominal volume was decreased also because the loosening
of the caudotruncus muscle made the gastralia rotate in a way. As the abdominal
volume decreased, then, air was forced out from the respiratory organs. Soon,
the tail and torso bounced up again, pulled by the elastic back musces, and air
was inhaled.
However, one thing troubles me. As Stephen Getesy
has shown, in most theropods the main extensor of the femur was the
caudofemoralis longus. Its insertion was a bump on the femur called the fourth
trochanter, and its origin the proximal tail. The example used by C&F
was a dromaeosaur, and dromaeosaurs may indeed have had quite athropied
caudofemoralis longus muscles, judging by their spaghetti tails and minute
trochanters. But in most theropods they were mighty indeed.
When a caudofemoralis longus muscle contracted, it
would have bent the tail downwards. The caudofemoralis longus was probably
active during the whole period of propulsion, so I think the tail would have had
hard time bouncing back upwards when the femur was swinging
posteriorly.
What do you think?
Best wishes,
Henri
Rönkkö |