From: rh@smds.com (Richard Harter)
Newsgroups: talk.origins
Subject: Re: Holden Numbering
Date: 14 Sep 92 08:51:07 GMT
Reply-To: rh@ishmael.UUCP (Richard Harter)
Organization: Software Maintenance & Development Systems, Inc.

--- I wrote ----

If a sauropod had held his neck up the way you hold your arm up, it would
indeed been in deep sneakers.  But it didn't, of course.  They had moderate
size cable running along the top of their vertebrae -- there is a big groove
just for that purpose.  The cable [actually a big ligature] was attached
all along the body of the sauropod.  Actually it ran both ways so, yes,
the tail and neck counterweighted each other.  

--- And Ted Holden replied ----

The conception described above is straight from lalaland.  Let me explain.

In the case of birds sleeping with legs bent, you truly can say that it
is effortless, since tendons totally suffice to hold the position.  This
means that the tendons would break if the bird were forced down past 
some point while in the same basic posture.

Were a sauropod's neck and tail to be permanently help up and supported
by such a system, then he would die of thirst within one more day than
as many days as he could go without water;  he would not be able to lower 
his neck to drink.

------

I'm guessing that Ted has some sort of picture in his head of what he
is talking about that justifies these statements.  God has been merciful;
I have a dispensation that relieves me of the duty of guessing at what
is in Ted's head.

Instead of trying to refute Ted's claim, let's talk about how sauropods
actually did support those necks and tails and how much freedom of
movement they had.  Let's talk about Brontosaurus [the real one, not
the official one.]

If you look at old Bronty's skeleton, we basically see four legs acting
as columns supporting two arches, front and back, with a long chain of
verterbae sitting on top of them.  The vertebrae between the pelvis and
the shoulder form an arch -- the neck and tail vertebrae point at a
downward angle at the pelvis and shoulder respectively.  The hind legs
are larger and support more of the weight -- approximately 60/40.
The vertebrae have a big groove which [presumably] held a tendon.

How was the neck supported?  The support was continuously distributed
but we can simplify the issue by thinking of the neck as rigid.  The
tendon running from the top of the body downwards takes up the torque.
The torso, which the cable is attached to, is the counterweight.  The
tail is supported in the same way.

The objection is raised that the neck would have to been rigidly in place
since tendons are inelastic.  [At least I think that's what Ted is
claiming.]  Not so.  If the neck were rigidly constructed it would be
pretty much fixed in place.  However the neck bones are vertebrae. 

Vertebrae are constructed like nested cups.  They have a neutral position
and some freedom of motion; to move from the neutral position requires
muscular work.  This means that the shape of the neck could be altered
by applying muscle power at the vertebrae.  The muscles do not have to
work against gravity, i.e. lift, because the support comes from the
main tendon.

When the shape of the neck is changed the center of gravity of the neck
may also move up or down.  Moving it up requires lifting by the back
muscles.  The tendon and its attachment have some elasticity -- the
muscle does its work by contracting and pulling on the tendon.

The thing to remember is although the main tendon would have indeed been
under tension, it would not have been in a straight line like the cable
in a crane.  The reason is that it was within a groove.  {Think of a
cable running through eye bolts.] 

The upshot is that Brontosaurus would have had no problem with getting
its head in the water.

------

Brachiosaurids were built a bit differently.

The tail and neck were not literally counterweighted, i.e. the tail did
not lift when the neck when down and vice versa.  However the tail and
neck did apply approximately equal and opposite forces on the main tendon.
-- 
Richard Harter: SMDS Inc.  Net address: rh@smds.com Phone: 508-369-7398 
US Mail: SMDS Inc., PO Box 555, Concord MA 01742.    Fax: 508-369-8272
In the fields of Hell where the grass grows high
Are the graves of dreams allowed to die.