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Re: circulatory systems
From: A really swell guy who plays go! <firstname.lastname@example.org>
> Over lunch an associate and I were discussing dinosaur circulatory
> systems. Apparently, neither of us know anything on the subject, or
> of any other large animals for that matter.
> We were wondering what is known or speculated on dinosaur anatomy. Is
> the heart just an enlarged version of an elephant's or perhaps a
Well, to start with, circulatory systems do not fossilize, so
we *know* very little. (Also, only the very largest of dinosaurs
would need a heart larger than an elephants, and the larger whales
exceed the size of the largest dinosaur by a fair margin).
Now, that said, there are some indications of what dinosaur circulation
may have been like. The first is phylogenetic: crocodiles are the
closest living relatives of the *ancestors* of the dinosaurs, and
birds are probably descendend from dinosaurs. Now, birds have a
four-chambered heart, albeit of a different structure than the
mammalian heart, and crocodiles *almost* have a four-chambered
heart - with an avian type structure. This strongly suggests that
most dinosaurs, if not all, had a bird-like four-chambered heart.
This is even more so since the valve between the ventricles in
the crocodilian heart is an adaption to its aquatic existance,
and when on land their heart is *functionally* four-chambered.
Also, the shape and size of the rib cage in the largest dinosaurs,
the saurpods, suggests a rather large heart, even relative to body
Finally, in many saurischians, especially advanced theropods,
the bones have pneumatic spaces similar to those found in birds.
Now, in birds one of the functions of these pneumatic spaces is
to allow the one-way flow, counter-current lungs that birds have.
Thus, theropods *may* have had avian style one-way lungs.
Beyond that, most everything is speculation.
The peace of God be with you.