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Re: sauropods: homotherm,heterotherm or gigantotherm?



I wrote:
> > Plus I felt they just glossed over the heart
> > morphology of pythons and varanids in an attempt
> to
> > explain why crocodylians have 4 chambered hearts
> (both
> > varanid & python hearts [possibly more species as
> > well] are functionally 4-chambered, and capable of
> > pressure separations equivalent to those seen in
> > mammals & birds).

--- David Marjanovic <david.marjanovic@gmx.at> wrote:
 
> How does that work?

+++++++++++++++++++++++++++++++++

Both groups have a muscular ridge separating a
majority of the ventricle. During muscular
contraction, this ridge meets the top of the ventricle
(bottom of atria) and forms a complete separation. The
result is a heart that is capable of achieving a
substantial pressure differential between pulmonary
and systemic sides, during each contraction. It makes
for a good example of how a 3 chambered heart could
become a 4 chambered heart.

Two years ago there was study done on ventricular
haemodynamics in _Python molurus_. The results found
the python was capable of producing systemic blood
pressure that was ~7 times higher than the pulmonary
side. That makes it, at least, as equivalent as the
pressure differential seen in humans. 

The full ref for that is:

Wang, T. Altimiras, J. Klein, W. Axelsson, M. 2003.
"Ventricular haemodynamics in _Python molurus_:
separation of pulmonary and sytemic pressures." The
Journal of Experimental Biology. Vol. 206. pgs
4241-4245

I apologize if I wound up sounding harsh in the last
e-mail. I haven't had any appreciable sleep for the
past week. It seems to make me sound (er, write)
cranky.

Jason.





"I am impressed by the fact that we know less about many modern [reptile] types 
than we do of many fossil groups." - Alfred S. Romer

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