Re: Mamenchisaurus Posture Paper

[Roger Seymour <roger.seymour@adelaide.edu.au>]

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.