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Re: Dino heart--Williston's prediction comes true!
At 09:35 30/04/00 -0400, you wrote:
> 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.
In general, any time you see the words 'primitive', 'advanced',
'sophisticated' etc. in biological discourse (all over the place,
unfortunately) just ignore them. They are hangovers from old ideas about
'progress' in broad scale patterns of evolution, for which there is no
evidence (none that can't easily be countered, anyway). Crocodile hearts
work fabulously well in crocodiles, and the fact that mammals, for
instance, have not been able even to loosen the crocodilian ecological
stranglehold on subtropical and tropical freshwaters over the last 65
million years just goes to demonstrate the point.
Best to all