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Re: Dino heart--Williston's prediction comes true!



At 09:35 AM 4/30/00 -0400, gejd@concentric.net wrote:
Folks,
    With respect to the "primitive" crocodilian heart, I saw a show on
Discovery channel or animal channel recently in which it is claimed that
the crocodilian heart is the most sophisticated one in existence. Rather
than having unoxygenated blood just sloshing into the oxygenated blood
stream, the heart allows blood to circulate in a closed loop to the
brain while shutting down blood flow to extremities, allowing a longer
time for the animal to stay underwater. This is an adaptation to an
"underwater lie-in-wait" predatory strategy.
    Does anyone know if this is correct? If so, crocodilian hearts may
be specialized to their lifestyle and not represent a primitive
condition prior to the split of dinosaurs from crocs.

It is essentially correct, though I would quibble about the phrase "most sophisticated".


The description is also somewhat confusing. The crocodilian heart switches between an effective four-chambered mode in the air, and a modified three-chambered mode when submerged. As discussed in previous articles here, this effects blood *pressure*.

So, yes it is possible, indeed very likely, that this condition is an adaptation to their aquatic lifestyle. This is the very basis upon which Williston made his hypothesis.

However, this does not settle the issue of the ancestral archosaurian condition. The earliest classical archosaurs, the so-called "proterosuchians", may also have been aquatic predators, in which case the switch-hitting heart may have evolved then. The fully four-chambered heart of birds (and presumably dinosaurs) would then have evolved from the crocodilian style heart when their ancestors abandoned aquatic hunting.

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May the peace of God be with you.         sarima@ix.netcom.com