Sauropods’ neutral neck postures were really weird
November 5, 2014
Last night, I submitted a paper for publication — for the first time since April 2013. I’d almost forgotten what it felt like. But, because we’re living in the Shiny Digital Future, you don’t have to wait till it’s been through review and formal publication to read it. I submitted to PeerJ, and at the same time, made it available as a preprint (Taylor 2014).
It’s called “Quantifying the effect of intervertebral cartilage on neutral posture in the necks of sauropod dinosaurs”, and frankly the results are weird. Here’s a taste:
Taylor (2014:figure 3). Effect of adding cartilage to the neutral pose of the neck of Apatosaurus louisae CM 3018. Images of vertebra from Gilmore (1936:plate XXIV). At the bottom, the vertebrae are composed in a horizontal posture. Superimposed, the same vertebrae are shown inclined by the additional extension angles indicated in Table 1. If the slightly sub-horizontal osteological neutral pose of Stevens and Parrish (1999) is correct, then the cartilaginous neutral pose would be correspondingly slightly lower than depicted here, but still much closer to the elevated posture than to horizontal. (Note that the posture shown here would not have been the habitual posture in life: see discussion.)
A year back, as I was composing a blog-post about our neck-cartilage paper in PLOS ONE (Taylor and Wedel 2013c), I found myself writing down the rather trivial formula for the additional angle of extension at an intervertebral joint once the cartilage is taken into account. In that post, I finished with the promise “I guess that will have to go in a followup now”. Amazingly it’s taken me a year to get that one-pager written and submitted. (Although in the usual way of things, the manuscript ended up being 13 pages long.)
To summarise the main point of the paper: when you insert cartilage of thickness t between two vertebrae whose zygapophyses articulate at height h above the centra, the more anterior vertebra is forced upwards by t/h radians. Our best guess for how much cartilage is between the adjacent vertebrae in an Apatosaurus neck is about 10% of centrum length: the image above shows the effect of inserting that much cartilage at each joint.
And yes, it’s weird. But it’s where the data leads me, so I think it would be dishonest not to publish it.
I’ll be interested to see what the reviewers make of this. You are all of course welcome to leave comments on the preprint itself; but because this is going through conventional peer-review straight away (unlike our Barosaurus preprint), there’s no need to offer the kind of detailed and comprehensive comment that several people did with the previous one. Of course feel free if you wish, but I’m not depending on it.
References
Gilmore Charles W. 1936. Osteology of Apatosaurus, with special reference to specimens in the Carnegie Museum. Memoirs of the Carnegie Museum 11:175–300 and plates XXI–XXXIV.
Stevens, Kent A., and J. Michael Parrish. 1999. Neck posture and feeding habits of two Jurassic sauropod dinosaurs. Science 284(5415):798–800. doi:10.1126/science.284.5415.798
Sauropod Vertebra Picture of the Week 
November 5, 2014 at 1:39 pm
I’ve just read the preprint. Figure 1 tells the story clearly.
So, one question is “Are there any extent animals with similar cervicals which we can use to test the hypothesis?” In other words, do any living creatures have a similar two-contact arrangement between adjacent certicals?
Another question is “what is the evidence that cartilage sat between the two vertebrae at the (lower) condyle/cotyle location, but not at the (upper) zygapophyseal location?”
November 5, 2014 at 1:46 pm
Hi, Michael, thanks for these thoughts.
Yes, pretty much every extant vertebrate has the same two-contact arrangement between consecutive vertebrae, humans included. In terms of gross morphological similarity, the best neck to play with would be a giraffes, since the cervicals are elongate and opisthocoelous (i.e. have ball-and-socket joints with the ball at the front). But as you can imagine, giraffe necks are not easy to come by. Camels might be next best, but they’re also somewhat on the rare side. (I always keen an eye out for interesting roadkill as I drive around the Forest of Dean, but I’ve yet to find a giraffe or a camel, sadly.)
Still, we could do some mechanical experiments using dry bones. Just articulate two consecutive vertebrae with the best fit you can achieve between the bones; then shove some padding between the centra, re-align the zygs, and see how much deflection you’ve caused. If anyone who has access to a giraffe or camel cervical sequence would like to try this (and document it), we’d love to know.
I guess the post wasn’t clear (the paper is better), but the there is cartilage between the zygapophyses — at least, each zygapophyseal facet has a coating of hyaline cartilage, and this is what articulates: contact is never bone-on-bone. But that doesn’t significantly affect neutral posture for two reasons. First, the zyg cartilage is much thinner than the intervertebral cartilage. And second, the zyg facets are oriented dorsomedially and ventrolaterally — not anteroposteriorly, so that adding cartilage between them doesn’t push the upper part of the vertebrae apart anteroposteriorly.
Great questions! Thanks for giving me the opportunity to clarify.
November 6, 2014 at 2:03 am
Good follow-up, Mike! I must say that I find trying to determine the effect that cartilage would have had on the length and shape of sauropods necks to be fascinating.
You linked to the preprint of your The neck of Barosaurus was not only longer but also wider than those of Diplodocus and other diplodocines submission – does this mean that it has not yet been formally published?
November 6, 2014 at 8:06 am
[…] a comment on the last post, Mark Robinson asked an important […]
November 6, 2014 at 8:07 am
Mark, you question about publication is so important that I ended up writing a whole post about it. Thanks for raising it.
November 8, 2014 at 4:01 am
I wrote an article for Prehistoric Times in which I had the front of then neck (half way) bent downward. It made a bend because I used Gilmore’s illustrations. Then Scott Hartman told me the illustrations don’t match the real specimen and the neck didn’t do what I wrote about. I’m still waiting for someone to publish a paper on the neutral neck so I can correct my article…maybe I can use yours when the paper comes out?
November 8, 2014 at 9:27 am
Hi, Tracy. Do you have a scan of that PT article? It would be interesting to see.
You are of course welcome to use my paper in any way you wish; but aware that the only aspects of the bone geometry that it uses are centrum length and zygapophysis height; and that the latter is measured off Gilmore’s plates. So whatever mistakes he may have made in the illustrations, my work will suffer from some of them, too.
November 11, 2014 at 5:57 pm
That is strange indeed. Perhaps the elasticity of the cartilage between the centra actually served to keep the neck up without muscle action – in other words, the cartilage was compressed in the neutral pose in life, as opposed to the pose shown here which seems to assume zero gravity?
But how did you estimate the amount of cartilage between the centra in the first place?
November 12, 2014 at 12:17 am
I am inclined to doubt that intervertebral cartilage in sauropods was compressed in a qualitatively different way from in other animals, though of course all animals compress it to some extent. In any case, holding the neck up without muscle action would require passive dorsal tension members. I don’t know of any extant animals that do that.
I used the cartilage thickness estimates from our recent PLOS ONE paper. See p5 of the preprint for a summary. (Actually, just read the preprint :-) It’s short and to the point, it’ll take you ten minutes.)
December 23, 2014 at 11:22 am
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