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



(I would have replied to this thread earlier but I was out of town.  The
following is an OVERLY-SIMPLIFIED answer.)

chris lavers wrote:

>  it is claimed that
> the crocodilian heart is the most sophisticated one in existence. 

As others have stated, sophistication is a tough term to use!  It seems
to me that all organisms are just as sophisticated as needs be for their
particular life style(s).

> 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? 

This is approximately correct -- but there is really more to it. 
Because the croc is an ectotherm, it needs different amounts of oxygen
under different conditions.  In colder underwater conditions, the
extremities do not need the oxygen they need when the animal is chasing
a tasty terrestrial intruder.  Thus most of the blood with high oxygen
concentration is shunted to the area of need (brain!).  Of course, some
oxygen does circulate in the extremities.

The other point is that the incomplete cardiac septum allows for some
mingling of the oxygenated and de-oxygenated blood.  During periods of
low metabolic need, the heart rate is slower and the blood mixes more
freely.  This decreases the need for oxygen intake.  During periods of
high metabolic need, the heart rate increases and the differences in
flow rates decrease the free mixing of the blood.  The animal then can
take in and utilize more oxygen while more efficiently giving off carbon
dioxide.

In essence the croc has the best of both worlds.  The variable flow
rates of the 3-chambered heart and the high-efficiency-when-needed gas
exchange of the closed 4-chambered heart.

There is more to the story.  If my diagrams were on the web, I'd include
the site.  Oh well.... (Visualize!)

Roberta M. Meehan, PhD