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RE: Sauropod ONP



Christopher Taylor (gerarus@westnet.com.au) wrote:

<One thought that seems obvious, but I'm not sure if it has been mentioned
(unless it was what Greg Paul was saying) - resting position and feeding
position of the neck were not necessarily identical.>

  Kent has also said this, in fact made a large provision for this in his
agreement with Greg Paul on the matter. Kent has used the modelling of the
vertebrae tou project maximal curves of neck vertebrae when infering various
percentiles of disassociation between zugapophyses while keeping the centra
connected. The issue, I think, is that some restorations and arguments would
imply that sauropods were engaging in neck elevating postures as a matter of
course, rather than constantly held horizontal. Similarly, if we consider the
sauropod "hoover-saurs" feeding mechanism by sweeping the neck around side to
side, we should in fact note that constant movement would be the norm, but that
some movements, i.e., side to side, yeild greater envelopes than others (up and
down). Thus, Kent argues the constraint in envelope extent shoudl warn us about
not just maximal movements for a given disassociation of neck bones, but also
general postures resulting from this.

  I noted earlier in this thread that artistic renditions of several argued
sauropods would have us think the average posture of the neck was elevated
(that is, in non diplodocoids, anyway), but the data on paper and as modelled
argues otherwise. Why a sauropod would raise its head above the floor so high
and risk blowing its head off without the use of theoretical arterial valves (a
theory to substantiate a theory seems shaky logical ground!) to slow the
pressure of fluids back into the brain, when there is an ample shoulder- or
foot-level supply of vegetation or the occassional squirrel to be had, I do not
know.

  It is clear that, in the same formation, in the same level, we do not seem to
get the same kind of sauropod neck at once, indicating possible constraints on
sauropod speciation and discretion in envelope patterns. In the Morrison, my
only regret is that we lack a neck for *Haplocanthosaurus* in which to consider
its relation to *Apatosaurus*' medium, *Diplodocus*'s long, *Barosaurus*'s
superbly long, and *Camarasaurus*'s short necks. *Brachiosaurus* seems to have
specialized in slightly higher vegetation, but the same foods were likely not
in resource competition between sauropods, as dentition tells us that different
foods were preferred, so where neck length may overlap, teeth and skull design
would seem to differ. The same should be true for the Shaximiao sauropod
faunae, where *Omeisaurus* and other "mamenchisaurs" exist in the same
formations, and tooth and neck discrimination may indicate resource
partitioning. So it seems rather more romantic and "aesthetic" to raise the
neck and argue that contradictory theories would be wrong.

  We should also consider straightening the spines of sauropods BEHIND the
shoulders as well, and other data is indicating the same for most theropods,
since ventrally-wedged dorsals seem rare to my knowledge. I've had to resist
bowing the dorsal series in my own restorations despite their elegant effect,
and find instead that an elegant sort of curve and thorax is produced by the
natural increase in neural spines and consequently dorsal vertebral height
posteriorly, and in the increasing pelvic depth, and the position and
orientation of the pectoral girdle. Much supported by fossil data on scapular
position and the trickier issue of how the specimens are arranged in life. I
find a little ease of mind comes from erring on the side of caution when
invoking taphonomic principles of muscular and tendinous contraction and
diagenic distortion of the bone itself, and consider this when reconstructing.

  I've only reconstructed the skeletons of two sauropods, one of a mount of
*Mamenchisaurus* and one of *Opisthocoelicaudia*. In the former, I restored it
following the mount, including dorsal arching, but held the neck horizontal for
ease. In the latter, however, I attempted to articulate the dorsals and caudals
neutrally, and found they form a largely straight line. I have no data to
consider this is not in fact an accurate position for them in life. If
restoring movement in skeletons, one should of course consider that the slopes
and curves will increase or decrease as neccessary, but when providing a
skeleton that is largely static, there is no reason to diminish the
effectiveness of the restoration by exaggerating features for "effect".

  Cheers,

Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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