Sauropod necks thread continued ...

["Matthew Bonnan" <mbonnan@hotmail.com>]

Hi Tom:

You said:
> It disturbs me that the model does not want to get _Camarasaurus_ necks 
> over
> the horizontal: it was CLEARLY capable of such without disarticulation, as
> documented by numerous fossils in opisthotonic death position: the CMNH
> juvenile, the USNM specimen on display, etc.

Whoa, don't get me wrong here.  No, no, no.  Of course it would be 
disturbing if they were using the model alone to predict neck placement!  I 
don't think I was too clear.

First off, they have modeled a giraffe neck in DinoMorph, and that went 
together and moved like a giraffe neck just using zygapophyseal info.  
Furthermore, the real preliminary stuff on Brachiosaurus (which was shown in 
the Discover magazine article) showed a relatively vertical neck, so again 
it's not like the program is somehow forcing everything to be horizontal.

However, take a look at Osborn and Mook (1921) and in that monograph, on a 
number of sauropods but with a lot of info on Camarasaurus, you find a 
restoration of the Camarasaurus skeleton -- and that restoration has the 
neck in a relatively horizontal position.  Now, Osborn, Mook, and the other 
grand old men of paleontology had access to these vertebrae before they were 
mounted, and perhaps in Camarasaurus, the vertebrae don't like to extend far 
beyond horizontal, again constrained by their zygapophyses.

Yes, you point me toward the CM and UMNH Camarasaur specimens.  In both 
cases, as you note, the neck is cranked up in a death pose.  Note, 
especially in the CM sauropod, many portions of the skeleton are 
disarticulated -- the scapulacoracoids have dropped down, the humeri are 
turned in, the antebrachium (ulna and radius) are disarticulated, and the 
two hands (manus) are turned out.  It is very difficult to tell what is 
going on at the base of the neck and body in that CM specimen because it is 
obscured by being only half exposed (only one side faces us, the other is 
still buried in the matrix) and the vertebrae at the base of the neck appear 
kinked up.  Furthermore, the zygapophyses appear to be very kinked together 
and it is very difficult to make out what's going.

However, your point is well taken.  We should always be skeptical of 
computer models, especially when they do not appear to reflect what we see 
in the bones.  However, we should be careful about relying too heavily on 
skeletons like the CM Camarasaurus as controls.  After all, would we 
conclude that the necks of Ornithomimid dinosaurs allowed them to swing 
their heads upside down over their backs because we find some in this death 
position?

I would venture to politely disagree with you regarding the articulation of 
disarticulated bones as controls.  From my own experience, skeletons trapped 
in rock or mounted present only one hypothesis or control of how the 
skeleton could have gone together.  By physically articulating dino bones in 
a number of positions, we can sometimes find limits or motions that we would 
not have guessed possible either from viewing skeletons in rock or those 
mounted, and as such open up new hypotheses and ideas of what the limits to 
motion were.

The beauty of computer modeling dinosaurs, if done as accurately as possible 
(and considering all the limitations we have with fossil material), is that 
we can articulate together sauropods and other heavy beasts without 
forklifts and prayers.  DinoMorph is only capabale at this point of modeling 
vertebrae, so most of my dissertation was a body building class: forklifts 
and prayers. =)  Can't wait to model those limbs in "virtual space" (but in 
cyberspace I could use my sauropods to do battle with Gibson's cyberpunks.  
Bring 'em on, Betty!). =)

In any case, Dr. Holtz has brought up some excellent, skeptical 
considerations of the Parrish/Stevens model -- this is always welcome.  The 
only way we make any progress in science is to continually refine our 
techniques and continually question our results.  Each day, with any luck, 
we get a little closer to reality.

Matt Bonnan

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