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Re: Sauropod Necks



bruceshillinglaw@netzero.net asked:

> Just a thought - if the neck of an apatosaur couldn't be brought
> above the horizontal,

I'm kind of surprised that Honored Person Matt Bonnan didn't comment
on this.  Hopefully that just means that he's distracted because he's
supposed to be writing his dissertation (instead of reading this
message, Matt! :-) Anyhoo, the paper described models of two
sauropods, the _Diplodocus_ upon which we've been focussing to date
and also _Apatosaurus louisiae_.  The model _Apatosaurus_ neck had
much more flexibility for dorsal flexion than the model _Diplodocus_
neck; even though it had a shorter neck, the model _Apatosaurus_ could
elevate its head 2 m higher (with all four feet planted on the ground)
than could the model _Diplodocus_.  Unlike the model _Diplodocus_,
the model _Apatosaurus_ could raise its head well above its back.

> where does that put the center of gravity? It seems to me that
> would make rearing __much_ more difficult, as the neck (and to a
> lesser extent the head) would be pretty influential 'way out
> there...

Honored Person Matt already addressed that, so I'll just throw in a
different point.  Parrish and Stevens suggested that since their model
indicates that _Diplodocus_ could lower its head to a position beneath
the plane upon which its feet stood (geography permitting), and since
the plants available to the animals as high browsers were probably not
very nutritious, _Diplodocus_ may have fed primarily along the shores
of lakes and rivers.  They could conceivably have even fed on plants
underwater as their feet were planted firmly on dry ground.

Well, actually I should throw in something else more closely related
to the original question.  The animals could pull their heads back and
to the sides to greatly decrease the lever arm of their necks.  The
model _Apatosaurus_ could reduce its lever arm by a factor greater
than 5 (of course this comes by increasing the lever arm in the
horizontal direction which means the animal would have to supply a
torque to prevent itself from rolling).  The model _Diplodocus_ could
only reduce the forward lever arm by about a factor of 2 (actually a
little less) by using this maneuver.  In any case, you can imagine
that if a sauropod were to rear, one way to do it would be to
essentially throw its head back and to the side.  Once the animal was
up off its front limbs it could more slowly bring its head to the
front, and the lever arm problem wouldn't be as bad as it was prior to
rearing since the head would now be closer to the center of mass
(along the rostral-caudal axis).  Since I'm not putting any numbers
here I'm not making any claims for plausibility at the moment.  Just
trying to give you more to think about.

-- 
Mickey Rowe     (rowe@psych.ucsb.edu)