RE: Centripetal Forces on a Horizontally Grazing Sauropoda

["Mike Milbocker" <mmilbocker@psdllc.com>]

There are 2 things needed: 1) a receptive bladder and 2) a returning force.
During the centripetal action blood would not flow if equal volumes of blood
had to both move toward the head and away, i.e., a non-distensible vascular
system. Therefore, a bladder is needed to allow blood to flow toward the
head without requiring blood to flow away from the head. The bladder could
simply be systemic dilation of the distal vessels. However, in this
situation the arteries would need to be valved to convert the potential
energy stored in the dilated vessels into uni-directional blood flow.

I believe giraffe's have valved arteries, but I'll leave that statement to
others to confirm.

The return force could be: 1) pressure built up in the bladder (much the
same as diastolic distension of the human heart), 2) elevation of the
well-oxygenated head to look for predators or to harvest high vegetation, 3)
a heart and/or 4) a tail swing.

Such a head/tail pumping system, whether or not assisted by a heart, would
probably have a quite different vascular layout. And I would not rule out a
primitive lung in the head that would provided CO2/O2 exchange across the
bladder membrane with or without a second one in the chest.



-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
Andrew A. Farke
Sent: Tuesday, April 13, 2004 4:22 PM
To: mmilbocker@psdllc.com; dinosaur@usc.edu
Subject: RE: Centripetal Forces on a Horizontally Grazing Sauropoda


How might the sauropod get blood *back* to the heart in this system? The
centripetal acceleration might work to get blood away from the thorax, but
wouldn't it also keep it from getting back? I don't know if it'd be as
simple as setting up a venous "siphon" system between the tail and neck, as
blood from the tail and blood from the neck empty into the heart via
different veins (posterior vena cava and anterior vena cava, and the whole
complication of the hepatic portal system, etc.).

Andy

> -----Original Message-----
> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu] On Behalf Of
> Mike Milbocker
> Sent: Tuesday, April 13, 2004 10:33 AM
> To: dinosaur@usc.edu
> Subject: Centripetal Forces on a Horizontally Grazing Sauropoda
>
> Centripetal Forces on a Horizontally Grazing Sauropoda
>
> It has been presented that sauropods kept their head and neck coplanar
> with
> the body and tail, and swung the neck, out-stretched in a circular path,
> called the browse plane, centered on the shoulder region.
>
> Assuming the neck length to be L, and the head makes one 180 degree
> transit
> in time t then the force, F, that would push blood toward the head is
> given
> by
>
> F = mar = m V2/L   where V = pL/t
>
> To give
>
> F = mp2L2/t2
>
> And
>
> ar = p2L2/t2
>
> Let L= 10m, then ar = 973/t2
>
> For ar to equal the acceleration of gravity (ar = 9.8 m/s2)
>
> t = 10 seconds
>
> This is not an unreasonably short period of time if the head were to be
> involved in warning the sauropod of danger.
>
> If the sauropod were raising its head in a circular trajectory
> perpendicular
> to the browsing plane, this would be the maximum time allowed in order for
> gravity not to impede blood flow, i.e., at this rise rate the blood would
> be
> "weightless".
>
> For faster motion, the head could actively fill with blood while rising.
> The
> table below gives the g's of force at various rise times:
>
> Rise Time             g's of force
>
> 10 s                  0.99
> 9 s                   1.23
> 8 s                   1.55
> 7 s                   2.03
> 6 s                   2.76
> 5 s                   3.97
> 4 s                   6.21
>
> Thus, the rapid motion of the head in a circular arc can create sufficient
> blood pumping forces.
>
> If the head and tail were swept asynchronously, the animal could create an
> efficient blood pumping system, independent of a heart. Combining feeding
> and defensive strategies with blood pumping may have allowed this class of
> animals to achieve their great size.