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reexamination of fused cervicals of Camarasaurus 5761 verifies dorso-flexion
When I was in NY a couple of weeks ago I visited the AMNH and took another
look at the co-fused Camarasaurus cervicals of 5761, the only set of sauropod
neck vertebrae that apparently preserve the degree of flexion at the neck base.
Kent has argued that these show that these sauropods definitely had a straight
rather than dorso-flexed neck base.
Before going further, the Osborn and Mook 1921 illustration of these verts is
accurate, but misses some key info.
In a recent post K said that the two 5761 cervicals will rock if set on a
hard surface because "the condyle is SMALLER in diameter than the cotyle. Get
it? Let me go through the reasoning: A) condyles fit inside cotyles, B)
cotyles have an inside and an outside diameter (the rim has a thickness), C)
cotyle inside diameter is larger than the condyle diameter to provide for said
cartilage. Therefore, the cotyle outside diameter is necessarily a bit larger
than the associated condyle diameter. How much bigger? Oh, about the amount
the condyle of C11 is above the foam."
That argument is spurious when it comes to 5761. The preserved angle on the
underside of the cervicals from the anterior condyle of 11, along the posterior
cotyle of the same, and then to the posterior cotyle of 12, is a strong 11
degrees of dorso-angulation. This is shown in Fig. 1 (captions below, Scott
Hartman has kindly posted the images for me as listed with the captions).
If the two elements are preserved articulated in a straight line then the
ventral angle would have to be balanced by the same degree of reverse
dorsally. If that were true, as shown in the top of Fig 1., then the posterior
cotylus of 11 would have a vertical diameter much greater than that of 12,
and would be about twice as deep as the anterior condyle of 11. That would be
very unlikely, and probably pathological. But fortunately there is no need at
all to estimate the depth of the posterior cotyle of 11.
It is not obvious in the old O&M figure, or in the photos that Kent has
posted, but the only things that have fused between the two cervicals are the
articular surfaces themselves, those of the centra and zygapophyses. The neural
arches and their zygapophyseal struts remain unfused.
This is great because in direct lateral view the usual opening that is
present between articulated vertebrae between the base of the neural arches and
upper rims of the centra is actually visible as shown by the photos in Fig. 2
and correctly restored in the bottom of Fig 1. A yardstick can be run right
through it from one side to the other. In the O&M figure this is shown as vague
dark spot in not quite the correct place rather than the opening that can be
seen all the way through. In the photos Kent posted one has to know they are
there to see them. When I took photos I carefully positioned the camera so that
the extent of the opening is maximized, and is also emphasized by a light
background in both directions in Fig. 2.
This means that we know exactly how deep the preserved posterior cotyle of 11
is. It is in fact a little shallower than that of 12, and only moderately
deeper than that of the same bone's anterior condyle. This of course makes
anatomical sense, is a nonpatholigical condition, and is therefore not at all
So we can now accurately measure the angle at the top of the centra. It too
is dorso-angled at almost 8 degrees as per the bottom of Fig. 1.
The preserved long axis angulation of the centra is of course simply the
average of nearly 8 and 11 degrees, or about 9 degrees of dorso-flexion.
Ergo, the only published example of preserved neck base angulation in any
sauropod to date is a strong 9 degrees of dorso-flexion.
This means that K's contention that the fused 5761 cervicals stand as perhaps
the best direct preserved fossil evidence that sauorpod neck bases were
normally straight is directly falsified. There is no ambiguity on this
issue, this case is closed.
(Hopefully K will change his comments on these vertebrae on his website.)
If anything the reverse is true. The co-fused cervicals stand as good
evidence that some sauropods had strongly dorso-flexed neck bases. The only way
avoid this conclusion is if the preserved dorso-flexion is due to crushing.
cannot be entirely ruled out, and the two bones are somewhat dorso-ventrally
crushed, but I could not see any particular reason to conclude that the
crushing increased the angle. Itâs more likely that dorso-ventral flattening
decrease the angle of dorso-flexion, but that is not verifiable. What is
needed, obviously, are more fused cervicals to see if the pattern is repeated
not. That will happen sooner or later, but is not worth holding oneâs breath
So it looks like an old camarasaur did indeed have two neck base vertebrae
fuse up at a dorso-flexion of about 9 degrees, and for the rest of the
discussion I will presume that is essentially correct. That tells us a lot of
As far as I can tell the zygapophyses are fused in completely neutral posture
close to or at 100% overlap. That means that before the two cervicals fused
the neutral life posture was probably about 9% dorso-flexed too. If so another
5-10 degrees of dorso-flexion could be achieved without disarticulating the
centra and zags. As I noted in earlier posts 9 degrees of dorso-flexion between
6 cervo-dorsals will pitch the neck upwards some 45 degrees, and this was
probably not near the maximum possible until the zags etc reached their
It would be great if the fused cervicals could be CT scanned in order to see
if it can be determined what lies between the fused ball-and-socket centra
articulations. My suspicion is that there was thick cartilage padding between
centra that created the 10 degree dorso-flexion with the zags in neutral
(For our listening and viewing enjoyment I inserted the fused 5761 cervicals
into one of the old droop necked Camarasaurus restorations K likes to see how
it works, which is not well at all as shown in Fig. 3 [Note that the original
restoration had one too many cervicals.] I reissue the challenge to anyone to
include the fused cervical pair as part of a plausible horizontal or drooping
neck. Only be breaking the fusion and ventro-extending the two vertebrae can
the neck base be properly depressed.)
K has pointed to the neck base cervicals of Camarasaurus CM 11069 as evidence
that they sloped downwards. It is worth noting that the first cervical
preserved in this series is not at neutral zygapophyseal position in the photos
posted, the zags are clearly strongly ventro-extended. If those zags are
retracted until they are at 100% neutral articulation then the cervical will be
strongly dorso-flexed relative to the rest of the series, resulting in an oddly
In any case there is no doubt that the preserved neutral dorso-flexion
between cervicals 11 & 12 in 5761 far exceeds that between the same neck bones
11069 when the zags of the latter are fully neutral and the centra
are closely spaced as they are in the restored series in the photos. So
whatâs going on? Individual variation is very possible considering the
seen in giraffe necks. But absence of the thick cartilage padding that is
probably ultimately responsible for the strong dorso-flexion of 5761 may be the
key factor. As I showed in an earlier post, it is not possible to keep the neck
of juvenile Camarasaurus CM 11338, with the zags in fully neutral
articulation, from articulating in a strong downward curve unless thick (about
total) cartilage pads were present.
I inspected the cast of 11338 at the MD Science Center and confirmed that
there is no space left between many or most of the dorsal centra, instead they
are jammed tightly together (Fig. 4). There is little doubt that in life
substantial cartilage padding was present. Why is the spacing not preserved?
death dehydration of the cartilage caused it to shrink, pulling the dorsals
tightly together. As explained in an earlier message, the same thing happened
the neck. The neck base vertebrae of 11338 are dorso flexed about 9 degrees
relative to one another on average, the same as that preserved in 5761 as shown
in Fig. 4. So there is no good reason to doubt that camarasaurs carried their
necks well above horizontal, could raise them to about vertical, and that thick
intervertebral cartilage, apparently ossified in 5761, was responsible.
That the two 5761 cervicals froze up dorso-flexed even thought the sauropod
needed to lower the head to ground level to drink indicates that habitually
holding the neck above horizontal was very important in selective terms when it
came to feeding habits. The myth that Camarasaurus was habitually going about
with its neck even close to, much less below, horizontal is busted. Ergo,
skeletal mounts with the neck elevated as per that at the Wyoming Dinosaur
It has been said by some on this list that Kâs argument rests upon hard
osteological rather than speculative soft tissue evidence, but this is not
The thesis by K that neutral neck posture in sauropods can be reliably restored
rests entirely on the premise that the spacing between centra was minimal
because the soft intervertebral cartilage was thin, which in turn is based on
preserved articulated specimens. This means that K is relying on the soft
having a certain characteristic, and the fossils faithfully recording it. But
this methodology is inherently unreliable because vertebral spacing can
obviously be easily altered post-mortem, so we have no way to accurately
the all critical cartilage thickness with sufficient accuracy in any case â
e. we are always guessing unless the cartilage is ossified fusing the
vertebrae which will happen rarely and to only two cervicals in a given
claim that intervertebral cartilage thickness is reliably recorded in
articulated skeletons is taphonomically naÃve. Kâs work is therefore highly
upon soft tissues, and is highly speculative.
It is much more scientifically conservative and accurate to concluded that
there is no way to reliably restore neutral neck posture in any sauropod
the cartilage thickness is almost never preserved in a manner that we can be
confident about. We can say that some sauropods clearly had thick
intercervical cartilage padding, and some normally carried their necks erect,
as shown by
the only direct, hard osteological evidence we have at this time, the fused
5761 cervicals. But since only two vertebrae of 5761 locked into neutral
posture, and obviously an entire neck series cannot fuse, we do not know the
neutral posture of even 5761 and never will for any other individual. We can
also say that most sauropods could easily elevated their heads far above
level, and many could probably even arc the head over the back, without
coming close to disarticulating the zygapophyses and centra.
Co-fused cervicals 11 & 12 of AMNH 5761 as figured by Osborn & Mook. Top â
unaltered, broken area of prezygapophyseal strut of 12 does not alter
conclusions. Bottom â corrected to show laterally visible interneural opening
and top of
posterior centrum of 11. In both the 11 degrees of dorsal angulation of the
ventral edges of the centra are shown. In the top figure the contrary 11
degrees of ventral angulation needed if the centra form a straight line is
indicated, this requires that the cotyleâs vertical diameter of 11 be far too
the bottom figure the actual dorsal angulation of nearly 8 degrees in accord
with the true height of the cotyle of 11 is indicated, as is the 9 degrees of
dorso-flexion of the centra.
The co-fused cervicals 11 & 12 of Camarsaurus AMNH 5761. Camera was oriented
to maximize visibility of interneural opening and top of posterior centrum of
Bottom figure is droop-necked Camarasaurus as restored by Osborn and Mook.
Above the number of cervicals is corrected to 12, and the dorso-flexed fused
cervicals 5761 are inserted.
The preserved dorso-flexion of adult fused cervicals AMNH 5761 compared to
those of juvenile CM 11338, former reduced in length to match latterâs. Note
that the dorso-flexion is essentially the same in both specimens, although the
adultâs zygapophyses are not dorso-flexed like those of the juvenile.
Post-mortem shrinkage of intervertebral cartilage â which has pulled most of
tightly together - is probably responsible for the latter condition.