new dino topic--long but (i think) interesting

[Kevin James Dracon <jconrad@lib.drury.edu>]

Hey, 

If this topic has been exhausted in recent times (but prior to September),
please ignore this.  However, I think I have something worthy of a little
discussion.

I just got a look at this month's issue of Discover magazine.  It has an
article on sauropod necks which I found intriguing.  It seems that they
are using computer generated dinosaurs skeletons to figure out how
sauropods moved and the posture of their necks.  THey suggested that the
natural position of the neck in  _Diplodocus_ and _Apatosaurus_ (I still
like "Brontosaurus") would have been only a few inches off the ground due
to the structure of the zygapophyses.  _Brachiosaurus_, on the other hand,
would have had a hard time lowering its head because the natural
orientation of its neck would have been a 55 (?) degree angle with its
back.  

The latter idea is not too hard to accept.  After all, we have modern
analogues to this condition (camels, llamas, and particularly giraffes).
THis is not to say that I believe this idea simply because we have modern
analogues, but that their evidence, along with the modern analogue does
make a more convincing case.   I have a bit of a problem with the former
idea though.  There are many reasons for this, not the least of which is
Bakker's argument of, if you're going to evolve a 10-30 foot neck, why
feed two feet from the ground?  (in the case of this article and
_Diplodocus_, a 20 foot neck to eat only 12 feet above the ground and
_Brachiosaurus_ with a 30 foot neck and its head only 18 feet above the
ground!)

My second idea about that posture is that it would create far more stress
on the neck.  _Mamenchisaurus_ had a reinforced neck and the idea of
holding it horizontal makes more sense in that animal (though I'm still
not completely convinced, see Bakker's question above) than it would in a
diplodocine.  It's like when you extend your arm with something in your
hand.  It's far easier to carry a small load with your had directly above

                            gravity
                               \/
 gravity                        o.
 \/ \/    ____                   |
o========/    |====-----         |
         ||--||                  \  ____
         --  --                   \-    |====-----
                                   ||--||
                                   --  --


your head than holding it horizontally.  Gravity stretches the weight out
if you extend your arm, but would concentrate it if you hold your hand up.  
Some might point to the tail as an example of where this theory is flawed,
but we should remember that the tail tapered more completely than the
neck, and did not have an esophagus or trachea running through it.  

THe Discover article also mentions that _Apatosaurus_ could have, given
the opportunity, place its head six feet ventral to its front feet.  Okay,
suppose that these ideas are correct, this seems to indicate that the
"tripodal" feeding posture of Bakker and others is correct.  Especially
this last about _Apatosaurus_.  Such would indicate that the animal could
reach through the trees to get the tidbits that they desire.  The 
horizontally positioned neck (in relation to the rest of the body) makes
sense in this scenario, because the animals would be re-alligning their

      __                     @@@@@@o
     /  \                       B   \
    o =/ \                      I    |
    T  \  \                     G    |   
    R   //\\  /--               T    \
    E  __  \_/                  R ==/ \
    E                           E   \  \    /--
                                E    // \  /
                               / \  __   --

bodies so that the back would be parallel or diaganol to the tree.  This
would also allow the non-brachiosaurid sauropod easy drinking postures
when not "tripodal".  I think it has been mentioned that the body could
have been supported against the tree while feeding.  The large first
digit unguals might have then served as anti-slip hooks (just an idea).  

It is also mentioned that conifers might not be a good food source for
sauropods.  However, pine needles have been found in association with
sauropod ribcages (of course, I think mollusc shells have too, but I doubt
they ate those), and the conifers which dominated the Jurassic flora would
have been an unrealized food source if sauropods did not consumer them.
Small ornithopods and stegosaurs would have been feeding low, but nothing
besides sauropods would have been feeding up high (in this case, above 20
feet).  

Anyway, this is my idea.  I don't mind being flamed if you have arguments
against me.  This idea is interesting to me and I welcome all viewpoints.
Besides, I to see new topics for discussion arise.  

Jack