We may never know how flexible sauropod necks were
November 8, 2018
The more I look at the problem of how flexible sauropod necks were, the more I think we’re going to struggle to ever know their range of motion It’s just too dependent on soft tissue that doesn’t fossilise. Consider for example the difference between horse necks (above) and camel necks (below).
The skeletons of both consist of vertebrae that are pronouncedly opisthocoelous (convex in front and concave behind), so you might think their necks would be similarly flexible.
But the balls of horse cevicals are deeply embedded in their corresponding sockets, while those of camels have so much cartilage around and between them that the tip of the ball doesn’t even reach the rim of the socket. As a result of this (and maybe other factors), camel necks are far more flexible than those of horses.
Which do sauropod necks resemble? We don’t currently know, and we may never know. It will help if someone gets a good handle on osteological correlates of intervertebral cartilage.
[This post is recycled and expanded from a comment that I left on a Tetrapod Zoology post, but since Tet Zoo ate that comment it’s just as well I kept a copy.]
Sauropod Vertebra Picture of the Week 
November 8, 2018 at 7:44 pm
Do alligators and birds show the same variation?
No easy answer in the large scale geometry? For example, I can’t tell from the x-ray how pronouncedly opisthocoelous the camel neck is, but it looks like it has has much deeper sockets.
November 9, 2018 at 1:14 am
One thing that might help a lot is specimens preserved that are undistorted or compressed. If we can assume the cartilage hadn’t dried (e.g. no opistotonic posture etc.) then the space between verts etc. is likely to be a *decent* proxy for the amount of cartilage in there. Of course that still may not solve things if you only know it for a few species and not others but it might help.
November 9, 2018 at 1:20 am
Yeah, but that’s a goodly helping of “if”. I don’t think, even if we found such a specimen, we’d trust it. Surely what we know of the taphonomy of extant critters makes it pretty much a non-starter?
What would be more helpful, I think, would be a survey of extant-critter vertebrae that concluded “animals whose cervical condyles are deeply embedded in the cotyles, like horses, have these characters in their bones, whereas those those with thick cartilage, like camels, have those characters”.
November 10, 2018 at 4:55 am
It’s funny you should mention that, Mike. Tanja Wintrich gave a great Romer talk this year at SVP, where she looked at exactly that. She did find some good osteological correlates for the presence of intervertebral discs vs. the slivers of cartilage seen in many birds and lizards. Currently the OCs can only provide a binary “there or not” statement, but it’s one step closer to figuring out how much cartilage was likely present between those discs.
November 10, 2018 at 9:32 am
That is great news! I don’t know if Tanja was aware of this, but I’ve twice blogged about how much this work needs doing (first one, second one), so I am delighted that someone is on this. Let’s hope there’s a publication on the way soon!
November 10, 2018 at 12:58 pm
But… that’s about intervertebral discs, which archosaurs aren’t supposed to have in the first place. Birds and crocodiles today definitely don’t.
November 10, 2018 at 1:01 pm
It’s about the presence or absence of intervertebral discs; and the next step after determining the nature of the cartilage is determining its extent.
BTW., how sure are you that crocs lack intervertebral discs? I seem to remember recently hearing that it’s not that simple.
November 10, 2018 at 1:08 pm
…but, yes, if you’re interested in the phylogenetic distribution of intervertebral discs, Tanja has been working on that.
December 6, 2018 at 1:06 am
Perhaps we could study the necks of Apatosaurines and compare them to creatures less low slung like Mamenchisaurids. I wouldn’t be surprised if there was some sort of correlate given how frequently Apatosaurines supposedly used them.
December 6, 2018 at 7:46 am
Ah, too bad I missed this when it was happening.
But… that’s about intervertebral discs, which archosaurs aren’t supposed to have in the first place. Birds and crocodiles today definitely don’t.
Sorry, that’s flatly incorrect. Some birds absolutely do have fibrocartilaginous joints between their free caudal vertebrae. This isn’t even obscure knowledge, it’s in the Nomina Anatomica Avium (Baumel, 1993), page 155:
“(60) Artc. intercorporalis (Barkow, 1 856). The joints between adjacent vertebral bodies in the cervical region and the cranial part of the thoracic region are synovial joints, some with intra-articular menisci (see Annot. 61-64, 7 1 , 74, 78). In the caudal thoracic region of some taxa, and the synsacral region universally, these joints become ankylosed, forming synostoses; the joints between the bodies of the free caudal vertebrae are symphyses (Columba, Baumel, 1988) or synovial joints (Gallus, du Toit, 1912-13).”
Tanja Wintrich is all over this stuff. I ran into her at SVP and we had a nice little stitch-and-bitch about how waaaay too many people in vert paleo and comparative anatomy don’t know about the firm evidence for fibrocartilaginous intervertebral discs in some lizards and birds. She has a paper in the works, probably submitted by now.
December 6, 2018 at 7:55 am
Wyatt, the problem is that we just don’t know that much about how, in life, the necks of apatosaurs or mamenchisaurs (or any other sauropod) were used. So, for example, if we knew that apatosaurs habitually held their necks erect but mamenchisaurs horizontal, we could look for osteological features that correlate with those behaviours — but we don’t, except by looking at osteological features in the first place, so we’re left with circular reasoning.
December 6, 2018 at 10:24 am
More, from Banerji (1957: p. 42-43), describing the intervertebral joints in the tail of a chicken:
“The joints between the bodies of the caudal vertebrae may be classified as secondary cartilaginous joints or amphiarthroses. A thick fibro-cartilaginous substance, the intervertebral disc, is interposed betweent two adjacent vertebral bodies. […]
“The cranial and caudal surfaces of each vertebral body are slightly amphicoelous. Each of these surfaces is almost kindey-shaped in outline with its long diameter the transverse one and the hilum looking dorsally. Each surface is covered by a thin plate of cartilage, which separates the fibers of the disk from immediate contact with the bone.
“INTERVERTEBRAL DISKS:
The intervertebral disks are bi-convex masses of fibro-cartilage that firmly connect the bodies of the adjacent vertebrae together. The outline of each disk corresponds to that of the bodies between which it is interposed. The disk is deeper ventrally, and this accounts for the ventral convexity in this region of the column.”
December 17, 2018 at 7:36 pm
[…] non-mammalian amniotes have exclusively synovial intervertebral joints (see the discussion in the comments on this post). I’m throwing in Banerji (1957), which is not cited in the presentation but which I did cite […]
December 31, 2018 at 3:02 pm
[…] was entirely representative of SV-POW!, with an eclectic grab-bag of posts on a museum mount, neck flexibility, a historical illustration, bird vertebrae, academic publishing, and what is probably our real […]
October 3, 2019 at 10:38 pm
Is there any physiological reason why the horse’s vertebrae are set so deep?
October 3, 2019 at 11:14 pm
Anton, I wish we knew. I file this in the huge stack of “things I don’t know about extant animals, either because I’ve not been able to find the relevant studies, or because they’ve never been done”.