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?