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Re: Sauropod Energetics (Peristaltic pumps for arteries?)
On Wed, Jan 25, 2006 at 04:28:35PM -0800, Guy Leahy scripsit:
> One problem with the peristaltic idea is that this type of muscular
> contraction is restricted to the digestive tract in vertebrates, and
> nothing like it is known for the vascular system for any extant
> vertebrate. One would have to postulate that sauropods evolved a
> structure not known to occur in any living animal, including taxa
> which are known to have elevated blood pressures. An additional
> problem is that this idea isn't testable. As I'd noted in another
> post, if Kent's reconstructions are correct, cardiovascular
> adaptations seen in living mammals and birds would work quite well in
> sauropods, without the need to postulate mechanisms for which there
> are no known extant examples... :-)
There are no known living multi-ton terrestrial quadrupeds with
pneumaticized skeletons, either.
Modern analogs are useful, but there just isn't anything all that much
like a sauropod around today.
Why not postulate a ciculation short loop in the neck that did gas
exchange along the walls of the air sacs? We know that the air sacs are
involved in respiration in the living example, we can argue convincingly
that the air sacks may have evolved from the respiratory system, so that
this use would be available to sauropods if the air sacs are basal to
saurischia, and we know that shunt valves evolve frequently -- you have
some in your hands -- in circulatory systems.
That gets you away from needing too large a heart, it doesn't involve
fundamentally different arteries, and it gets you effective rearing
feeding. It might even be testable if there's evidence of increased
vascularization in the walls of an vertebral air chamber.
Sauropod necks _had_ to have been complicated; postulating a relatively
minor degree of additional complication to go along with the rearing
adaptations isn't particularly stretching the point, even if it's
arterial pumping of blood by peristalsis.