[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Hopefully this 5761 cervical dorso-flexion thing can be settled -finally

At SVP I presented a poster on neck posture in sauropods, with emphasis on 
the fused cervicals 11 & 12 of Camarasaurus AMNH 5761. As I have shown earlier 
this year on the list they are dorso-flexed ~9 degrees. Just after I put the 
poster up I did a dope slap and realized I forget the nice lateral view 
photographes I shot of the pair from both sides in the spring with Carl's help 
at the 
AMNH. Yet another Homer Simpson moment. But I figured what the heck since the 
figure in left lateral of the fossil from Osborn and Mook 1921 is very 
accurate -- so what could be the problem?

I started to realize what when Jack McIntosh said Kent Stevens was saying 
something about the lateral flexion of the two cervicals. During the poster 
session Kent came by and indeed noted that in dorsal view the cervicals are 
a few degrees towards the right. Neither of us had measurements on exactly how 
many degrees (maybe 10?), but as shown by the photos cited below it is not 
extreme. Kent argued that the dorso-flexion in left lateral view was an 
do to the rightwards kink and the dorso-flexion is not present in right 
lateral view. I said nah because the dorso-flexion is the same in direct, I 
direct, lateral view on both sides. (Geometrically it is not possible for the 
actual degree of vertical flexion to be different in direct lateral view from 
one side to the other no matter what lateral flexion is present -- think about 
it) Kent called up some digital photos but they were not definitive because 
his right side views are taken from a somewhat oblique dorsal view, and the 
back end of the series was hidden by another bone laying on the supporting 
platform so we could not do measurements off his images. We agreed the 
evidence on hand was insufficient. 

So, on Scott Hartman's website at 
http://skeletaldrawing.com/sauropods/gp_cam_photo.jpg, for your listening and 
viewing pleasure, are the photos I took. 
They are in direct lateral view, hence in both views you can see straight 
through the slender opening between the top of the posterior centrum of 11 and 
anterior zygapophyseal strut of 12. As you can see, the dorso-flexion is 
exactly the same on both sides, so the rightward kink is not creating any 
of dorso-flexion. To repeat what I have said earlier on the list. Both the 
postero-ventral rim of the centrum of 12, and the antero-ventral rim of the 
centrum ball of 11, are well clear of the mat, into which is pressing the 
postero-ventral rim of the centrum of 11. So these cervicals rock. The angle 
these three points is strongly dorso-flexed, to the same degree in both views 
course. The postero-dorsal edge of the rim of the centrum of 11 is a little 
bit below the level of the postero-dorsal edge of the rim of the centrum of 12, 
and the antero-dorsal edge of the ball of centrum 11. So that line too is 
dorso-flexed, in both right and left views - of course. 

The next question is how many degrees of the two verts dorso-flexed. This 
cannot be measured off the photos because the postero-ventral rim of the 
of 11 is sunk into the mat, because shadows obscure that location, and because 
there is a pathological projection hiding that location on the right side. 
The Osborn and Mook figure is accurate and unobscured' so using that the 
dorso-flexion is about 9%. The bones are crushed a little dorso-ventrally, 
but that should have suppressed the dorso-flexion if anything. 

So, there is no doubt that cervicals 11 & 12 of 5761 as preserved are 
significantly dorso-flexed. Not straight, not depressed. Case closed on that 
Hopefully Kent will modify his website on this point, and if he still wants to 
argue otherwise he needs to provide figures with measurements. 

5761 is a very large, and presumably was a very old, camarasaur. It had to be 
able to depress its head and neck enough to drink. Yet it's neck base 
vertebrae fused in an upwards slope despite this critical need, probably making 
drinking more difficult for the poor old beast. This means the normal 
pressure to hold the neck high was very strong, and this was its habitual neck 
posture. Thus the only actual evidence we have of cervical series posture in 
any sauropod confirms an upwards slope. There is no reason to think these two 
cervicals were unique in being dorso-flexed, so I suspect the other half dozen 
cervo-dorsals were similarly pitched upwards, giving the neck a 45 degrees plus 
slope. But we can never be sure about the exact degree of upwards pitch of 
the neck. As I have discussed earlier and in the poster the lack of 
of the all critical intervertebral cartilage makes restoring actual, living 
neck posture in sauropods a fool's game. Just can't be reliably done. Likewise 
the orientation of the cervical series in different giraffe specimens I 
included in the poster ranges from strongly erect to strongly downarced, 
because of differing degrees of ossification of the intervertebral cartilage. 
Not that it matters much in functional terms because animals rarely actually 
feed at neutral neck posture. And every sauropod could feed with the neck held 
essentially vertically, in most cases when quadrupedal, and in all cases when 

Bruce Rothschild came by my poster and I asked him what might have caused the 
5761 pathology. After saying a number of medical things beyond my knowledge 
base he said it would require further examination. It would be very useful to 
CT scan the (as far as I know uniquely) co-joined cervicals to determine the 
disease, better measure the orientation, and see how thick the intervertebral 
cartilage, although it would require a very large industral machine to do it.