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THOUGHTS ON SAUROPOD NECKS
The debate concerning sauropod necks and their in-life use is good.
Here are my views, following on from recent comments proferred by
Concerning the weight of some of the big guys, Brian said..
> "Three-digit tonnage"? I think you've *seriously* overestimated the
> weight of sauropods. _Argentinosaurus_ is the only known sauropod
> that *might* fall into that category, but only Don Lessem thinks it
> weighed in excess of 100 tons.
Well, Dale Russell was quoted in the _Science_ article that first
reported _Argentinosaurus_ that he felt that this animal may well
have weighed upwards of 100 tons - it is not just a Lessemism (god
help us if it was). Of course, Brian is very correct in that
virtually all other sauropods - including _Mamenchisaurus_ and most
diplodocids - were considerably less weighty. Current estimates put
these animals between 10 and 35 tons, or thereabouts.
> And don't discount the weight of that 30+ foot neck. Anteriorly-
> tapering cervical vertebrae or no, that neck still weighed a
> significant amount.
Sauropod vertebrae and sauropod necks would have been incredibly
light when not fossilised. It is reasonable to think that one could
actually pick up a very big _Brachiosaurus_ cervical vert with one
hand. I was thinking two hands, but Per Christiansen (an expert in
mathematical models of scaling in tetrapods) reckoned otherwise when
I recently spoke to him at a conference.
As you'll know, there is overwhelming evidence that sauropod
cervicals were highly pneumaticised, and there was probably more air
to them than bone. Dino Frey and John Martin now have good evidence
for a new model of the sauropod neck, based on osteological
correlates seen in croc dissections, and they find it highly
pneumatic with a.. well, they will present this at SVPCA (September
1998). Sauropods do seem to have reduced the mass of their necks
considerably, and apparently minimised on any structure that might
have added weight (another argument against trunks or fleshy lips).
This is also in agreement with models where necks are nearer
horizontal than vertical.
And somewhat regretfully, I am coming down on the side of those who
believe that mamenchisaur necks were nearer the horizontal than they
were the vertical. The reason is the cervical ribs. Where portions of
cervical ribs overlap, they cannot slide across one another, but are
bound by ligaments that allow comparatively little craniocaudal
extension. This system is now pretty well understood in crocodile
necks (thanks to Dino's dissection papers) where the ligaments that
bind consecutive cervical ribs mean that, when the neck is
straightened, the ligaments will pull it back to natural curvature
with no muscular effort. The point is that the overlapping portion of
any two cervical ribs cannot be extended beyond the portion of
You can see extensively overlapping cervical ribs in some
theropods (notably in _Coelophysis_, where a rib will extend the
length of the following five cervicals), and also in sauropods like
_Mamenchisaurus_ and _Omeisaurus_. Ergo, these are relatively
inflexible necks that must be held in a position that does not warp
the rather straight shape of the cervical ribs. If you look at
skeletal mounts of long-necked sauropods like _Omeisaurus_ where the
neck has been put in an S-curve, you will see that the cervical ribs
are not aligned in parallel as they should be (and as they are in the
articulated necks of fossils and in the _M. hochuanensis_ mount,
which has a horizontal neck - contra Wilson and Sereno 1998, this
taxon does exist), but are sticking out away from the reconstructed
curve of the neck - not good if you imagine the thing as a live
animal (and yes, I know that live bone would have been more supple,
but the cervical ribs already have a slight curvature, plus the
degree of bending that would have been needed in life to fit the
ribs to the S-curve neck is just too much).
Near-vertical sauropod necks mean that, assuming these animals had to
lower their necks to drink (yes yes, something else that has been
flogged to death recently), extensive sliding across cervical rib
overlaps has to be allowed. As argued above, this is not possible.
Basically, reconstructed long-necked sauropods with near-vertical
necks actually means that their necks would have been *less* flexible
than if their necks were horizontal, because of these cervical rib
Finally, one thing that really jumps out when you (or at least I)
examine a sauropod mount is how wide the base of the neck is. These
are not slim necks, well demarcated from the thorax, but
mediolaterally *broad* structures that are essentially cranial
extensions of the body. In camarasaurs and brachiosaurs especially
(funnily enough, I haven't ever seen a titanosaur mount:)), seen from
above or below, the neck tapers from the shoulders toward the head,
and does not have a constriction at the base that is then continued
cranially at the same width (as per out necks). As you can see in the
reconstructions in Wilson and Sereno (1998), and as Greg Paul shows
for his diplodocids and his newly modified _Brachiosaurus brancai_
(and as Czerkas and now Tracy Ford say as well), near-horizontal
necks that extend from the thorax are correct.
One area that still troubles me is the alleged upward curve at the
base of some sauropod necks, as figured by Greg Paul in the recent
_DinoFest_ volume. This curve has been accentuated by post-mortem
contraction of neck ligaments and, while it may support an upward
curve at the base of the neck in some sauropods, continuing curvature
so a near-vertical neck results is probably not correct and
near-horizontal necks are not perfectly horizontal anyway. Again,
this is a matter that will be addressed in the near future and I
cannot give too much away.
On related subjects that I could talk about (but will not, for the
sake of time).. giraffes have 8, not 7, cervical verts. One of them
has become the first thoracic - a fact that was recognised in the
last century. Plesiosaurs necks: another contentious subject. All
evidence now indicates that plesiosaurs necks were moderately, but
not overly, flexible.
"Yeah, but you didn't measure cat skins, perform morphometric
analyses, or do population censuses"
"No, we have a life" - - Downes, 1998.