A fused atlas and axis in Apatosaurus
February 19, 2009
Here are the first two cervical vertebrae of the Carnegie Apatosaurus, from Gilmore’s 1936 monograph. As you can see, they are fused together. It is a bit weird that we haven’t covered the morphology of the atlas-axis complex here before. And sadly we’re not going to cover it now. I needed to get an image of these verts to a group working on…something secret…and this turned out to be the fastest way to get them the information in a format that would be easy to find for future reference. Hope you don’t feel used.
UPDATE: Here’s something weird: the both verts have facets for cervical ribs, but the cervical ribs had not fused to the vertebrae, even though they normally do, and despite the fact that the vertebrae had fused to each other, even though they normally don’t.
Sauropod Vertebra Picture of the Week 
February 19, 2009 at 9:14 pm
I do feel used, but in a good way.
It looks as if all that’s left of the atlas (as a free-living vertebra) is just the front fifth or sixth of the complex, plus the bit labeled “Ne” and the (assumed) rib. Right?
February 20, 2009 at 12:46 am
I think you mean something else weird… it’s all weird!! (Why wasn’t we told about this atlas/axis complex before? ;-) Cover it soon, someone, huh? Please?!)
Ah, but are those ribs fused to each other, is what I wants to know…
Do you guys ever feel like just making up something really weird? Cos if you did, I reckon that’s what it would look like. I mean it’s weird… like a Klein bottle or alembic or car-part or antique furniture/architectural detail, or something. It’s for real, right?
February 20, 2009 at 1:03 am
Yeah, I feel used: you knocked my nice, new Xenoposeidon post off the front page after only two and a half days!
February 20, 2009 at 6:16 am
Hmm. . .looks like a sauropod trying to be a ceratopsid, but failing miserably. ;-)
February 20, 2009 at 10:37 pm
[…] Here’s the mandated sauropod vert picture, which I believe has not appeared on this site before. I stole it from Darren as a gift to Mike–the poor widdle fing. […]
March 10, 2009 at 4:43 am
one word: DISEASE.
March 10, 2009 at 5:26 am
one word: DISEASE.
Maybe. I am not convinced, for two reasons.
First, any disease serious enough to cause fusion of vertebrae ought to have other, systemic effects. This individual also had a couple of fused caudals, but the fusion there does not match the fusion of the cervicals. The cervicals are not distorted, there is no florid proliferation of new, pathological bone, and there doesn’t appear to be any involvement of the ligaments spanning the vertebrae. It just looks like they simply welded together with no distortion of any kind, much like the fused posterior dorsals in Eomamenchisaurus. In contrast, the two affected caudals are both partly obscured by new bone growth that totally covers the centra where they make contact. That new bone growth probably involved some of the ligaments around the vertebrae. So the fused caudals don’t seem to have been caused by whatever caused the fused cervicals. And more importantly, there is no other sign of disease or pathology in the animal, which is not what you’d expect if disease was the culprit. If these vertebrae are all the way fused, there ought to be lots of others in intermediate stages, but there aren’t.
Second, these bones simply don’t look diseased. Unless Gilmore’s artist was given to fabrication*, they are a nice, symmetrical, normal-looking axis and atlas. They don’t have any erosion or pitting or reactive bone growth or other evidence that the periosteum was irritated or pathological. They’re just two normal-looking vertebrae that happen to be fused.
* On the subject of fabrication in Gilmore (1936)…it’s well worth reading what he has to say in the text about the posterior cervicals of CM 3018, the holotype of A. louisae.
So if I don’t buy disease in this case, what are the alternative hypotheses? Injury is always a popular one, but again, this doesn’t look like an injury, everything is nice and neat. It could have been arthritis specifically in the axis-atlas joint, that wore down the cartilage between the vertebrae until they welded together. We are so used to thinking of arthritis as a systemic problem (like rheumatoid arthritis) that it is easy to forget that arthritis can simply be a mechanical problem affecting a single joint. That’s not wholly satisfying, because no other cervicals seem to be affected, but then the atlas and axis have a special role in head rotation that is not shared with the rest of the column. I don’t know whether that counts as special pleading or not.
The fact is, there are quite a few fusions like this in sauropods, with no bone proliferation and no apparent infection or violence to the affected vertebrae (as opposed to the more proliferative fusions commonly attributed to DISH), in which the verts look fine, they’re just stuck together. I don’t know what the answer is yet. But I’m working on it. As always, stay tuned!
March 10, 2009 at 11:29 am
Matt, have you actually seen this material? Or are all your thoughts on it based on a low-resolution scan of an artist’s impression of a speculative reconstruction? We know from bitter experience how misleading the pretty plates in monographs can be.
June 17, 2009 at 2:22 am
[…] first, here is that photo of a another fused atlas-axis complex that you ordered (seriously, what’s up with these things?): Camarasaurus grandis YPM 1905, […]
March 15, 2010 at 8:02 am
[…] turn up a lot (see discussion here), and the fusion of the atlas to the axis is not unheard of (see here and here), fusion of the middle or posterior cervicals is rare. Which makes intuitive […]
September 9, 2013 at 3:46 am
[…] A fused atlas and axis in Apatosaurus […]