[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Sauropod necks thread continued ...



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

______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com