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RE: Sauropod necks thread continued ...



\> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Matthew Bonnan
> 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.

That is promising to here about the giraffe (an even better control than
using articulated fossils, since we *know* about the giraffe neck mobility)
and interesting about _Brachiosaurus_.


> 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.

Aha.  Well, that's good to know.  (I was aware of the disarticulation in the
appendicular skeleton, but hadn't looked in detail at the verts).

> 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?

:-)

Quite.  Obviously death positions do not necessarily (and probably only
rarely) reflect the life position of the animal.  Nevertheless, these
skeletons DO show us limits on the bone mobility, without concern of the
soft tissues.  For example, if DinoMorph would not allow the bones of
ornithomimids to assume the opisthotonic position I would be very cautious
about the software: we know the bones can assume that position.
Nevertheless, I wouldn't advocate that ornithomimids ran around looking
backwards and upside during life (rampant speculation alert 404: okay,
*maybe* they did so in elaborate mating rituals, like cranes), and such a
position might have done some nasty things to soft tissues in the throat
(then again, maybe not: see cranes).

> 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.

Well said: never intended to say that articulated fossils were the ONLY
controls, simply that they were one potential control.  I would love to have
3D bones out of the matrix of _Archaeopteryx_ or some compsognathid, so see
what these guys looked like when they weren't rendered 2D...

> 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. =)

I know the feeling: I once had to help out (then-classmate, now Curator of
Fossil Reptiles at the National Science Museum in Tokyo) Makoto Manabe in
comparing a proximal sauropod humerus from Japan with sauropod humeri in the
AMNH collection.  I could manage moving the _Diplodocus_ humeri by myself,
but it was a team project to move _Camarasaurus_ and _Apatosaurus_
material...  That's why I like working on small animals, like
_Tyrannosaurus_ and _Acrocanthosaurus_... :-)

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796