Re: Mamenchisaurus Posture Paper

[don ohmes <d_ohmes@yahoo.com>]

If a sauropod were immersed in water and lowered the
head below the heart it would again be pumping blood
"up" a pressure gradient, although with the assistance
of gravity. Is this correct? 

How deep (vertical head/heart distance) could the
heart pump blood, after accounting for gravity?

--- Roger Seymour <roger.seymour@adelaide.edu.au>
wrote:

> 
> 
> frank bliss wrote:
> 
> > I honestly don't know the answers to the following
> since I have not
> > ever really focused on the big guys as they didn't
> appear to hang out
> > up here on the Montana/Wyoming border.  Why do
> sauropods have to hold
> > their necks up high?  The advantage of a long neck
> may have been like a
> > long arm, reaching out and picking up sweet
> morsels instead of reaching
> > up.  The tail counterbalances and a really big
> lawn mower is born (so
> > to speak).  Is the mainstream opinion that they
> were high browsers? (Do
> > their neck verts allow articulation in that way?)
> Is it necessary to
> > look for a mechanism to allow high browsing when
> it may not have been a
> > method used for feeding.  (Granted it has to be
> thought out.)
> 
> Yes, I believe that the high browsing is favored,
> and some (including the
> Barosaurus in the AMNH) have sauropods tripoding to
> reach higher.   I prefer
> the vacuum cleaner analogy: a less mobile body with
> a long flexible feeding
> head that could reach from ground up to a couple of
> meters above the
> shoulders.  This would allow access to a great deal
> of food.
> 
> > Another
> > metaphorical analogue  comes to mind.... How much
> vertical distance
> > does a large whale have from its heart to it's
> brain when it is
> > swimming straight up?  It has to be several
> meters. Does water pressure
> > alter the mechanism somehow?  Did the big
> sauropods spend most of their
> > time browsing in lakes below the water level
> instead of terrestrially
> > feeding or is it all conjecture at this point with
> no data to support
> > either hypothesis?
> >
> 
> In water, gravity is not a problem, because the
> hydrostatic pressures in the
> blood column are practically matched by external
> hydrostatic pressures that
> transmit through the soft body tissues.  We studied
> blood pressure in land
> and sea snakes.  The sea snakes have relatively low
> blood pressures and if
> you take them out of the water and hold them
> head-up.  Their hearts cannot
> support the blood column and circulation stops in
> the brain.
> So whales do not worry about blood pressure
> problems; they seem to have
> slightly lower BP than expected, but there are no
> really good data on them
> under natural conditions.  They are in their own
> 'gravity suits', like
> pilots.
> Aquatic sauropods would also be protected from BP
> problems, using their necks
> to reach deep vegetation (or ?) while keeping the
> lungs near the surface to
> ease the strain of breathing.
> 
> 
>