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In a message dated 96-01-26 16:40:43 EST, pharrinj@PLU.edu (Nicholas J.
Pharris) writes:

>Yes, but all of the secondaries mentioned above are well attested by 
>fossils--except for the heart, of course.  The croc heart, as I 
>understand it, is essentially four-chambered, but there is a valve that 
>can allow mixing of blood when the animal is submerged and therefore 
>cannot breathe.

That could well be a vestige of a developmental stage of the quadricameral
heart. The QH did not arise from the tricameral heart overnight.