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RE: Sauropod cervical vertebrae

>From:  Nick Longrich[SMTP:longrich@phoenix.Princeton.EDU]
>       In general, the diplodocid neck stuck straight out or down
>slightly, although I seem to remember that Apatosaurus yahnapin had a neck
>with an upward bend at the base. Camarasaurus has such a bend, and so the
>neck did not stick straight out, but the relatively shallow angle on the
>articulation between neck and skull mean that it probably didn't stick
>straight up. Brachiosaurs have an upward inclination to the spine, an
>upward bend at the base of the neck, and a nearly 90 degree angle between
>head and spine (work on semicircular canals indicates that the heads were
>held more or less horizontally) all indicate that the head was held very
>high. I think Mamenchisaurus and many other Chinese sauropods also had the
>upwards inclination. 

McNeil Alexander did some work on the biomechanics of the truss
structure in sauropod necks - I believe it is in his Dynamics of
Dinosaurs book.   The implication is that the diplodocid necks were
supported in large part through tension in the ligaments on the dorsal
(top) neural spines on the cervical vertebrae.

This should allow a fair amount of upward flexion by increasing tension
- as occurs in many other vertebrates with similar structures (I believe
Alexander compares them to studies of deer and turkey necks).

Mamenchisaurus on the other hand, had ossified tendons in the neck, up
to 5 feet long as I recall, which supported the neck by being under
compression in the ventral side of the neck.   There are claims that it
was therefore much stiffer and  mainly swung from side to side for
efficient browsing.
>       There has been a lot of speculation as to whether the hearts would
>allow this, but the bones seem to say that it did happen. Perhaps long
>forelimbs and rearing were  ways to gain extra height without increasing
>the load on the hearts and vascular systems too far- either rearing or
>elongate forelimbs would increase the height of the head, but not increase
>the distance between neck and heart. 

Alexander comes to the conclusion that the heart dynamics are quite
possible - albeit more than any living animal (Giraffe is the highest).
 As you point out above the case for a high neck in Brachiosarus is very
strong.   So, at least one sauropod must have had the necessary vascular
system.  They others may have as well.