Atlantal ribs of the Carnegie Diplodocus, Moscow and Vienna casts
April 27, 2024
Eighteen months ago, I noted that the Carnegie Museum’s Diplodocus mount has no atlantal ribs (i.e. ribs of the first cervical vertebra, the atlas). But that the Paris cast has long atlantal ribs — so long the extend past the posterior end of the axis.
There were two especially provocative comments to that post. First, Konstantin linked to a photo of the Russian cast (first mounted in St. Petersburg but currently residing in Moscow). I’ll reproduce it here:
Carnegie Diplodocus, Russian cast, head and anterior neck in left lateral view showing smallish, straight atlantal ribs. Our thanks to Konstantin for this photo.
As you can see, there are atlantal ribs on this specimen, but they do not resemble those of the Paris cast. These are much shorter, narrower, and lacking in structure. I have not to my knowledge seen anything like this on any other Diplodocus, and my guess — it’s only a guess — is that these were added by the Russians at some stage in this specimen’s very complex history.
But wait, there’s more!
In another comment on the same post, Crown House linked to a 3D model of the Vienna cast that has been posted to Sketchfab. It’s a pretty low resolution model, but if you zoom and pan, you can see that it has large and complex Paris-style atlantal ribs:
Carnegie Diplodocus, Vienna cast, head and anterior neck in left lateral view, showing large atlantal ribs.
Although these resemble the atlantal ribs of the Paris mount, they are not identical: the wavy margins face posteriorly rather than anteriorly as in both the Paris mount and Holland’s (1906) illustrations; and the proximal end has a dorsal expansion.
So we seem to have (at least) four different state of atlantal ribs in different casts of the same Diplodocus:
- Absent in Pittsburgh and London
- Small and rod-like in Moscow
- Long with a wavy dorsal margin in Paris
- Long with a wavy ventral margin and a proximal dorsal expansion in Vienna
Can anyone offer informed speculation on how this state of affairs came about?
But then things get weird. If you manoeuvre your way around the model to look up at this region from below:
Carnegie Diplodocus, Vienna cast, head and anterior neck in left ventrolateral view, showing lateral processes of the atlas.
Well, what the heck are we seeing here? There are two spiny processes, one on each side, projecting laterally from the ventral part of the atlas, and swept back at mid-length.
I have never seen anything like this in any sauropod — or, come to think of it, any other animal, but I admit I don’t pay much attention to other animals.
Does anyone have any idea what these projections are? Remember you can go to the model and look at them in 3D.
Sauropod Vertebra Picture of the Week 
April 27, 2024 at 11:04 pm
I’m not sure if I’m looking at the same structure you are, but what it looks like to me is that the neural arches of the atlas have been mounted incorrectly so that their postzygapophyses flare out laterally rather than articulating with the prezygapophyses of the atlas.
Thanks to you and Crown House for bringing my attention to this 3D model! That’s super cool.
It is rather strange that there are so many different ways the ribs of the atlas-atlas complex have been portrayed on different casts of the same mount. It looks like the rib on the NHMW cast might be the element Holland described as the axis rib, mounted upside down from how Holland interpreted them?
April 27, 2024 at 11:12 pm
I rather think those spikes are too, well, spiky to be the atlas postzygs.
I did wonder if they had mounted casts/sculptures of the atlantal ribs illustrated by Holland (1906), but both them upside down. But then when I saw the proxmal expansion of the atlantal ribs, I changed my mind.
April 28, 2024 at 12:45 am
As casts of this dinosaur occur at various museums around the world and it is known when they received them it would be interesting to see how those ribs changed over time.
Did someone alter them as more information came in or what.
April 28, 2024 at 1:47 am
In Frankfurt/Main (Germany) in Museum Senckenberg is another cast of the Carnegie Diplodocus. I have checked my best photo from head and the first cervical vertebrae and i think, in this cast are no atlantal ribs.
April 28, 2024 at 6:36 am
I *think* they’ve tilted the atlas forward, and have the atlas cervical ribs sticking out sideways from the atlas. Maybe. I can’t imagine what else would be going on.
EDIT: …and maybe the longer, more correctly-placed ribs actually go with the axis? Because otherwise I’m not seeing any axis cervical ribs. The model is too low-res for me to tell if the correctly-placed ribs are supposed to be articulating with the atlas or the axis.
April 28, 2024 at 7:14 am
@LeeB, this is exactly the kind of thing I am trying to find out. On the whole, museums do <i>not</i> keep careful records of such things. The whole process of establishing such details is really more like being a detective than a scientist.
@piratrabevonrhyolith, thank you for checking the Frankfurt <i>Diplodocus</i>. This is not a Carnegie cast, though, it’s a completely different specimen!
@Matt Wedel, I don’t think that can be right. First, the laterally directed spikes are not only oriented differently from the atlantal ribs of any other sauropod I’ve seen, they are also differently proportioned. And secondly, the Carnegie axis comes with small cervical ribs already attached to the anterior part of the axis (see Hatcher 1901:figure 6).
April 28, 2024 at 5:21 pm
I’m going to throw in two cents here but, are you sure this isn’t a deliberate artistic attempt via preparation to brace the skull on the mount ?!?
I know that comment is pretty far out. Just saying …..
April 28, 2024 at 9:23 pm
Just to confirm, we are talking about the wing-like projections that extend laterally from the atlas to a width about equal to that of the skull, right? I still think they look more like atlas neural arches than anything else. Note that the atlas does not appear to otherwise have neural arches in this model. Alternatively, perhaps they’re incorrectly mounted proatlases.
I’m not quite sure what the proximal dorsal expansion on the atlantal rib of the Vienna cast that you’re referring to is.
Because the axial ribs of CM 84 are incomplete, I wouldn’t put it past people to have simply mounted more complete axial ribs on top of them.
Is AMNH 969 the only sauropod specimen that putatively preserves both atlantal and axial ribs?
April 28, 2024 at 9:37 pm
@John D’Angelo, yes, the sort-of wing-like processes. It’s hard to see them as atlas neural arches, but I admit I don’t have a better suggestion — or even a worse one, come to think of it.
On the atlantal rib of the Vienna mount: look at the proximal or anterior part of the rib, where it articulates with the centrum. There is a rounded dorsally directed process.
AMNH 969 is the only sauropod specimen that I know of for which both (putative) atlas and axis ribs have been described. But it’s more than possible that I have overlooked others.
April 29, 2024 at 5:32 am
Sounds like you have yourself a project fit for crowd sourcing.
There were casts of D. carnegii sent to London, Paris, Berlin, Vienna, Bologne, St Petersburg, La Plata, Madrid Mexico City and Munich.
The St Petersburg cast has been moved to Moscow since.
I wonder how many paleontologists or just people with cameras you know of who could be asked to go and photograph the front of the necks of these casts in exchange for getting mentioned in any paper that eventuates.
Also for comparison there is a Diplodocus cast in Frankfurt as mentioned; also one in Minnesota and another in Copenhagen.
The last is probably being studied but the other two could be photographed.
You probably know of other specimens that could be looked at, perhaps in New York?
April 29, 2024 at 11:41 am
Yaay, Diplo is back!
Mike, you do still have the fotos I made last year, don’t you? If not I can resend them; they also still are on Dropbox.
I try and post a link to one of them, don’t know if it works:
https://www.dropbox.com/scl/fo/ixihv5ow3l6p9o9pkwpdt/h?rlkey=3gbhgczz2im4bv3762qp97u3g&st=9hw9nrgf&dl=0
I also did a google search about other mounts and found some fotos online, long story short:
Bologna seems to have atlantal ribs;
La Plata seems not to, but possibly had some in the past;
Madrid is unclear, one foto shows them without, one with ribs
Are you interested in some links or do you already know all this?
@dale mcinnes The atlas does not touch the cranium, what looks like a connection is a digital artifact.
@LeeB The Vienna cast was remounted at least once (somewhere in the nineties?). It also seems to have been stored away during WWII, so there is a possibility that it was remounted incorrectly. This is speculative, but at least to my lay mans eyes it does look like somebody was not 100% sure what he was doing.
April 29, 2024 at 1:38 pm
Crown House : Yes. It’s better to have the original specimen at hand than relying on artifacts from photos. I stand corrected.
April 29, 2024 at 9:36 pm
CrownHouse, thank you, yes I still have your email thread and a note to myself in the in-progress manuscript to add material based on them. Yes, links to the other cast’s photos would be handy!
April 30, 2024 at 8:12 am
An update; there is also an over 80 percent complete D. longus skeleton in a mall in Dubai which may also be photographable.
It is claimed to be the most complete Diplodocus skeleton around; I don’t know how accurate that is.
April 30, 2024 at 8:15 am
@LeeB interesting! Although my primary concern right now is casts of the Carnegie <i>Diplodocus</i>, I’d certainly find photos of other diplodocine mounts relevant to my interests.
May 1, 2024 at 2:24 am
Well if you are interested in other Diplodocine mounts someone should photograph the mounts in Singapore.
I don’t know if they are Diplodocine or Apatosaurine or something else but they surely need looking at.
May 1, 2024 at 11:09 am
Oh, Frankfurt isn’t a Carnegie cast? o.O I thought so since my time at school…thank you for this info!
May 1, 2024 at 11:13 am
No the Frankfurt Diplodocus is from the AMNH. See https://digitallibrary.amnh.org/items/2ad880fc-bc4b-45bf-9f60-71f066bb2422