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Re: sauropod necks



  I have also reconstructed sauropod necks using the splice and glue method,
both literally and digitally. I have also done this for some theropods. If GSP
thinks there are more kinks and disarticulations in sauropods he's not
reconstructed than those Kent has, he's not tried the method too much on
theropods, some of which show bends far greater in neutral articulation than
any sauropod.

  In many cases, my method has gone a step further, since I also try to make
sure the anterior "ball" fits into the posterior "cup", and to do this I will
remove sections of the digital vertebrae and create a double layering, so that
the "ball" fits "under" the "cup" of the anterior vertebra, which is on an
underlying, because I wish to put the prezygapophyses "over". It takes some
finagling, and it can be better done in 3D, but I lack the software and never
had the time to sit and learn the modelling skills to "invent" vertebrae.
Nonetheless, the technique is easier on paper than on the computer, but the
result is the same. It also reveals a problem with trying to use the "ball" and
"cup" to articulate vertebrae, and it's one Kent brought up, one I repeated,
and one no one seems to have responded to as an issue when it comes to placing
vertebrae in articulation.

  There is, it seems, a dearth in the literature of attempting to measure,
model, and describe the precise shape of the "cup" of the posterior vertebral
central cotylus; it's depth, the slopes of the surfaces, and the angle of the
deepest point from the center of the "cup"'s rim, which might imply the actual
"fit" of the anterior "ball". Some artists have presumed that there is a
certain amount of soft-tissue between vertebrae, a safe bet, and the usual
number I hear is a decent 10%. I've not seen much research on verifying this
model in living animals with such vertebrae (crocs come to mind), and those
such as giraffes with mildly ball-and-socket articulations which much withstand
greater leverage forces as a result of being bigger and more terrestrial -- but
not to discard the possible effects of smaller, heavy, huge headed animals
versus animals that lightened the skeleton in a terrestrial existence. The
neccessity of figuring out how tight the vertebrae articulated in the cervical
series will permit how much movement the "cup" will allow the fitted "ball" to
move, and thus the deeper the fit, the tighter the contraint. GSP seems to put
half the "ball" into the "cup" and this seems a nice mesure, but he's not
presented any data to back his positions up. Note that during dessication,
animals' necks MOVE AROUND, and as in my previous critique of using the
juvenile camarasaur as a model for cervical flexibility, they will
disarticulate and taphonomic and geologic forces will "conspire" to distort
[pun, yes, I know] our knowledge of the natural position of the neck without
compeletely disarticulating it.

  And thus another point should be made, one Kent has also brought up but which
has been lost, it seems: sauropod vertebrae are rarely wholly and cleanly
preserved as in life, but as in all bones undergo diagenic mineral
transformation and thus will contract, expand, and often change shape as their
mineral makeup changes from apatite to whatever. Geologic forces will compress
vertebrae, and may also compress two adjacant vertebrae in different
directions. Just looking at the dorsal vertebrae of the FMNH tyrannosaur,
"Sue", should give us all pause to consider that diagenic distortion MUST be
taken into account, and this is likely what is resulting in people
misinterpreting the photos of fossilized bones as "real life pictures". I've
just completed a series of restorations on microraptorians (*Sinornithosaurus*,
*Microraptor*, and whatever NGMC 91 is...) and found myself entirely unable to
restore LPM 0200, the holotype of *Cryptovolans pauli* [please disregard
Czerckas' specimen number, as this was applied PRIOR to the specimen's
accession into a museum, at which point the specimen which was routed from the
CAGS became the propery of the Liaoning Paleontological Museum, or LPM, at
which point it was photographed by Xu and Norell for the purpose of
description]. The specimen itself is smashed and broken, with no single bone
seemingly whole and in many cases without a single consistent diameter
preserved, preventing any capability at even determining a length that I could
affirm was realistic. In furtherance of this diagenic issue, Inez Horovitz
recently in _JVP_ considered the holotype of the palaeanodont *Ernanodon* to be
compiled from at least two different specimens, due to the nature of problems
of shape and length of left and right sides, with left forelimbs shorter, and
right hindlimbs shorter, and an undistorted (mostly) skull. Yet as it turns
out, as originally reported by the original authors, Ding et al., they report
in a more recent issue of _JVP_ that the specimen was collected as a largely
articulated single specimen with vertebrae, skull, limbs all largely in place
as in life. Thus the limbs underwent disparate distortion, an effect that would
bear much taphonomic investigation.

  So we should be very wary about how we treat the shapes of sauropod verts
when, as in Kent's reproduction of the *Apatosaurus* vertebrae, or
*Brachiosaurus* SII series, some vertebrae in the row CAN'T articulate because
the prezygs are too high, or the vertebra has been squeezed and thus lengthed
dorsoventrally, and this will distort the shape of the "cup" and cause it to
even develop a more ventral plane from the anterior plane formed at the "ball"
because of this squeezing. Anyone crushing a wax-paper cup at the local
watering hole in one's office can readily discern this issue. Thus one must
investigate the bones themselves, and not rely on the figures or photos in side
view to determine the shape of the neck. A kink in side view can be real, or
just a bad angle, or a distortion in the bone not visible in the photo. It may
require a personal examination to do this. Of the people who've commented so
far, I know Kris has photographed mounts, I am sure Greg has as well, but Scott
and Kent are the only ones it seems who have gone to each one and examined them
element by element in person, and one should value this personal experience as
being worth the time it takes. Kent's illustrations are graphical ideas, but
they, unlike my digital splicing, are not meant to be the source of data, only
a graphical presentation. We should consider this before calling someone
"wrong".

  Cheers,

Jaime A. Headden

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

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