Here’s D10 and the sacrum of Diplodocus AMNH 516 in left lateral and ventral view, from Osborn (1904: fig. 3). Note how the big lateral pneumatic foramina, here labeled ‘pleurocoelia’, start out up at the top of the centrum in D10 and kind of pinch out up there, seemingly entirely absent by S3 (although there is a suspicious-looking shadowed spot above and behind the sacral rib stump labeled ‘r3’). Then on S4 and S5 the big foramina are back, but now they’re low on the centrum, ventral to the sacral ribs. In ventral view, the foramina on D10, S1, and S2 aren’t visible–they’re both over the curve of the centrum, and in the case of S1 and S2, obscured by the sacral ribs. But in S4 and S5, the big lateral foramina are visible in ventral view.

I’ve been interested in a while in this seeming hand-off in centrum pneumatization from dorsolateral, which prevails in the dorsal vertebrae, to ventrolateral, which prevails in the posterior sacral and caudal vertebrae. Almost all sauropod dorsals have the pneumatic foramina quite high on the centrum, sometimes even encroaching on the neural arch. But if sauropod caudals have pneumatic fossae or foramina on the centrum, they’re usually quite low, and almost always below the caudal rib or transverse process (there may also be pneumatic fossae on the neural arch and spine)–for evidence, see Wedel and Taylor (2013b). To me this implies two different sets of diverticula.

I think that in part because sometimes you get both sets of diverticula acting on a single vert. Here’s the centrum of sacral 4 of Haplocanthosaurus CM 879 in right dorsolateral view; anterior is to the right.

Here’s the same thing annotated (yeah, it does look a little like an Ent who is alarmed because his left eye has been overgrown by a huge nasal tumor). This vert has two sets of pneumatic features on the centrum: a big lateral fossa below the sacral rib articulation, presumably homologous with the same feature in S4 of the Diplodocus above; and a smaller dorsolateral fossa above and behind sacral rib articulation.

Unfortunately, CM 879 doesn’t tell us much about how these two sets of diverticula might have changed along the column. The centra of S1-S3 were not found, S5 lacks both sets of fossae, the first caudal has fossae both on the centrum, below the caudal rib, and low on the arch, and the second and subsequent caudals lack both sets of fossae. (I wrote a LOT more about pneumaticity in this individual in my 2009 air sacs paper, which is linked below.)

Working out how these diverticula change serially is a tractable problem. Someone just needs to sit down with a reasonably complete, well-preserved series that includes posterior dorsals, all the sacrals, and the proximal caudals–or ideally several such series–and trace out all of the pneumatic features. As far as I know, that’s never been done, but feel free to correct me if I’ve missed something. I’m neck deep in other stuff, so if someone wants that project, have at it. (If you happen to look into this, I’d be grateful for a heads up, so we don’t run over each other if I do get a yen to investigate further myself.)

References

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A couple of times now, I’ve pitched in an abstract for a Masters project looking at neck cartilage, hoping someone at Bristol will work on it with me co-supervising, but so far no-one’s bitten. Here’s how I’ve been describing it:

Understanding posture and motion in the necks of sauropods: the crucial role of cartilage in intervertebral joints

The sauropod dinosaurs were an order of magnitude bigger than any other terrestrial animal. Much sauropod research has concentrated on their long necks, which were crucial to their success (e.g. Sander et al. 2010). One approach to understanding neck function tries to determine neutral posture and range of motion by modelling the cervical vertebrae as a mechanical system (e.g. Stevens and Parrish 1999).

The raw material of such studies is fossilised vertebrae, but these are problematic for several reasons. The invariable incompleteness and distortion of sauropod neck fossils causes fundamental difficulties; but even given perfect fossils, the lack of preserved cartilage means that the bones are not shaped or sized as they were in life.

Ignoring cartilage has dramatic consequences for neutral posture, range of motion and even length of necks: pilot studies (Cobley 2011, Taylor 2011) found that intact bird necks are 8–12% longer than articulated sequences of their dry bones, and that figure is as high as 24% for a juvenile giraffe neck. A turkey neck postzygapophysis was 26% longer when cartilage was included than after being stripped down to naked bone.

We do not yet know how much articular cartilage sauropods had in their necks, nor even what kind of intervertebral joints they had: crocodilians have fibrocartilaginous discs like those of mammals, while birds have synovial joints, so the extant phylogenetic bracket is uninformative.

The project will involve dissection and measurement of bird and crocodilian necks, documenting the extent and shape of articular cartilage, identifying osteological correlates of fibrocartilaginous and synovial joints, and applying this data to sauropods to determine the nature of their neck joints and length of their necks, to reconstruct the lost cartilage, and to determine its effect on neutral pose and range of motion.

Following completion, we anticipate publication of the project.

References

Cobley, Matthew J. 2011. The flexibility and musculature of the ostrich neck: implications for the feeding ecology and reconstruction of the Sauropoda (Dinosauria: Saurischia). MSc Thesis, Department of Earth Sciences, University of Bristol. vi+64 pages.

Sander, P. Martin, Andreas Christian, Marcus Clauss, Regina Fechner, Carole T. Gee, Eva-Maria Griebeler, Hanns-Christian Gunga, Jürgen Hummel, Heinrich Mallison, Steven F. Perry, Holger Preuschoft, Oliver W. M. Rauhut, Kristian Remes, Thomas Tütken, Oliver Wings and Ulrich Witzel. 2010. Biology of the sauropod dinosaurs: the evolution of gigantism. Biological Reviews 86:117–155. doi:10.1111/j.1469-185X.2010.00137.x

Stevens, Kent A., and J. Michael Parrish. 1999. Neck Posture and Feeding Habits of Two Jurassic Sauropod Dinosaurs. Science 284:798–800. doi:10.1126/science.284.5415.798

Taylor, Michael P., and Mathew J. Wedel. 2011. Sauropod necks: how much do we really know?. p. 20 in Richard Forrest (ed.), Abstracts of Presentations, 59th Annual Symposium of Vertebrae Palaeontology and Comparative Anatomy, Lyme Regis, Dorset, UK, September 12th–17th 2011. 37 pp. http://www.miketaylor.org.uk/dino/pubs/svpca2011/TaylorWedel2011-what-do-we-really-know.ppt

(Obviously some part of this have since been covered by my and Matt’s first cartilage paper, but plenty has not.)

I now think there are two reasons no-one’s taken up this project: first, because I wrote it as very focussed only on the question of what type of joint was present, whereas there are plenty of related issues to be investigated along the way; and second, because I wrote it as a quest to discover a specific treasure (an osteological correlate), with the implication that if there’s no treasure to be found then the project will have been a failure.

But I do think there is still plenty of important work to be done in this area, and that there’s lots of important information to be got out of comparative dissection of extant critters.

If anyone out there fancies working in this area, I’d be delighted. I’d also be happy to offer whatever advice and help I could.

Update (18 October 2014)

Somehow I’d forgotten, when I wrote this post, that I’d previously written a more detailed post about the discs-in-sauropod-necks problem. If you’re interested in the problem, you should read that.

One aspect of sauropod neck cartilage that’s been overlooked — and this applies to all non-avian dinosaurs, not just sauropods — is the configuration of the cartilage in their necks. It’s not widely appreciated that birds’ necks differ from those of all other animals in this respect, and we don’t yet know whether sauropods resembled birds or mammals.

Here’s a classic sagittal view of a mammal neck — in this case a human — from The Basics of MRI (Joseph P. Hornak, 1996-2013):

sagittal-neck

You can see two distinct kinds of structure alternating along the neck: the big, square ones are vertebral centra (slightly hollow at each end), and the narrower lens-shaped ones are the intervertebral discs.

In mammals, and most animals, we find this distinct fibrocartilaginous element, the disc, between the centra of consecutive vertebrae. These discs have a complex structure of their own, consisting of an annulus fibrosus (fibrous ring), made of several layers of fibrocartilage, surrounding a nucleus pulposus (pulpy centre) with the consistency of jelly.

IntervertebralDisc

But in birds, uniquely among extant animals, there is no separate cartilaginous element. Instead, the articular surfaces of the bones are covered with layers of hyaline cartilage which articulate directly with one another, and are free to slide across each other. The adjacent articular surfaces are enclosed in synovial capsules similar to those that enclose the zygapophyseal joints. You can see this in the hemisected Rhea neck from last time:

Figure 18. Cartilage in the neck of a rhea. Joint between cervicals 11 (left) and 10 (right) of a rhea, sagittally bisected. Left half of neck in medial view. The thin layers of cartilage lining the C11 condyle and C10 cotyle are clearly visible.

Taylor and Wedel (2013c: Figure 18). Cartilage in the neck of a rhea. Joint between cervicals 11 (left) and 10 (right) of a rhea, sagittally bisected. Left half of neck in medial view. The thin layers of cartilage lining the C11 condyle and C10 cotyle are clearly visible.

The difference between these two constructions is very apparent in dissection: in birds, adjacent vertebrae come apart easily once the surrounding soft tissue is removed; but in mammals, it is very difficult to separate consecutive vertebrae, as they are firmly attached to the intervening intervertebral disc.

Figure 19. Alligator head and neck. Sagittally bisected head and neck of American alligator, with the nine cervical vertebrae indicated. Inset: schematic drawing of these nine vertebrae, from ([62]: figure 1), reversed.

Taylor and Wedel (2013c: Figure 19). Alligator head and neck. Sagittally bisected head and neck of American alligator, with the nine cervical vertebrae indicated. Inset: schematic drawing of these nine vertebrae, from ([62]: figure 1), reversed.

To complicate matters further, thin articular discs occur in the necks of some birds — for example, the ostrich (see illustration below), the swan, and the king penguin. But these discs do not occur in all birds — for example, they are absent in the turkey and the rhea. When they are present, these articular discs divide the synovial cavity and prevent the (cartilage-covered) bones on either side from ever articulating directly with each other, just like the articular discs in the human temporomandibular and sternoclavicular joints. These discs are thinner than the true intervertebral discs of mammals and crocodilians; and they are different in composition, lacking the annulus/nucleus structure and consisting of a simple sheet of fibrocartilage.

Taylor and Wedel (2013: Figure 4). Intervertebral articular discs of an ostrich (not to scale). Left: first sacral vertebra in anterior view, showing articular disc of joint with the last thoracic vertebra. Right: posterior view view of a cervical vertebra, with probe inserted behind posterior articular disc. The cervical vertebra is most relevant to the present study, but the the sacral vertebra is also included as it shows the morphology more clearly. These fibrocartilaginous articular discs divide the synovial cavity, like the articular discs in the human temporomandibular and sternoclavicular joints, and should not be confused with the true intervertebral discs of mammals and other animals, which consist of a nucleus pulposus and an annulus fibrosus.

Taylor and Wedel (2013: Figure 4). Intervertebral articular discs of an ostrich (not to scale). Left: first sacral vertebra in anterior view, showing articular disc of joint with the last thoracic vertebra. Right: posterior view view of a cervical vertebra, with probe inserted behind posterior articular disc. The cervical vertebra is most relevant to the present study, but the the sacral vertebra is also included as it shows the morphology more clearly. These fibrocartilaginous articular discs divide the synovial cavity, like the articular discs in the human temporomandibular and sternoclavicular joints, and should not be confused with the true intervertebral discs of mammals and other animals, which consist of a nucleus pulposus and an annulus fibrosus.

Crucially, the extant phylogenetic bracket (EPB) does not help us to establish the nature of the intervertebral articulations in sauropods, as the two extant groups most closely related to them have different articulations. As noted, birds have synovial joints; but crocodilians, like mammals, have fibrocartilaginous intervertebral discs. So their most recent common ancestor, the ur-archosaur, could equally have had either condition, and so could its various descendants.

vertebral-joint-type-cladogram

This seems like a mystery well worth solving. For one thing,  in the wholly inadequate database that we assembled for the paper, the birds had much thinner cartilage than the other animals. Since they are also the only animals with synovial neck joints, thin cartilage correlates with this kind of joint — at least across that tiny database. Is that correlation reliable? Does it hold out across a bigger sample? Is there a causation? If so, then finding out what kind of intervertebral joints sauropods had would help us to determine how thick their cartilage was, and so what their actual neutral posture was.

But we can’t tell this directly unless we find sensationally well preserved specimens that let us see the structure of the cartilage. We might speculate that since birds have unique saddle-shaped joints and sauropods have ball-and-socket joints like those of mammals and crocs, they’d be more likely to resemble the latter in this respect, too, but that’s rather hand-wavey.

Can we do better?

If we can, it will be through osteological correlates: that is, features of the bones (which are preserved in fossils) that are consistently correlated with features of the soft tissues (which are not). We’d want to find out from analysis of extant animals what correlates might exist, then go looking for them in the bones of extinct animals.

A couple of times now, I’ve pitched this as an abstract for a Masters project, hoping someone at Bristol will work on it with me as co-supervisor, but so far no-one’s bitten. Maybe next year. It would be a very specimen-based project, which I’d think would be a plus in most people’s eyes.

Figure 8. Cervical vertebra 7 from a turkey. Anterior view on the left; dorsal, left lateral and ventral views in the middle row; and posterior on the right.

Taylor and Wedel (2013: Figure 8). Cervical vertebra 7 from a turkey. Anterior view on the left; dorsal, left lateral and ventral views in the middle row; and posterior on the right.

Anyway, the awful truth is that at the moment we know spectacularly little about the cartilage in the necks of sauropods. We don’t know whether they had true intervertebral discs. If not, we don’t know whether they had articular discs like those of ostriches. We don’t know how thick these elements, if present, were. We don’t know how thick the hyaline cartilage on the bones’ articular surfaces was, or how evenly it covered its those surfaces.

And until we know those things, we don’t really know anything about neck posture or range of movement.

There’s lots of work to be done here!

The LSE Impact blog has a new post, Berlin 11 satellite conference encourages students and early stage researchers to influence shift towards Open Access. Thinking about this,  Jon Tennant (@Protohedgehog) just tweeted this important idea:

Would be nice to see a breakdown of OA vs non-OA publications based on career-stage of first author. Might be a wake-up call.

It would be very useful. It makes me think of Zen Faulkes’s important 2011 blog-post, What have you done lately that needed tenure?. We should be seeing the big push towards open access coming from senior academics who are established in their roles don’t need to scrabble around for jobs like early-career researchers. Yet my impression is that in fact early-career researchers are doing a lot of the pro-open heavy lifting.

Is that impression true?

We should find out.

Here’s one possible experimental design: take a random sample of 100 Ph.D students, 100 post-docs, 100 early-career researchers in tenure-track jobs and 100 tenured researchers. For each of them, analyse their last ten years of publications and determine what proportion are paywalled, what proportion are free to read (e,g, on arXiv or in an all-rights-reserved IR), and what proportion are true (BOAI-compliant) open access.

An alternative approach would be to randomly sample 1000 open-access papers (from PLOS and BMC journals, for example), and 1000 paywalled papers (from Elsevier and Springer, say) and find the career-stage of their authors. I’m not sure which approach would be better?

Who is going to do this?

I think it would be a nice, tractable first project for someone who wants to get into academic research but hasn’t previously published. It would be hugely useful, and I’m guessing widely cited. Does anyone fancy it?

Update

Georg Walther has started a hackpad about this nascent project. Since Jon “Protohedgehog” Tennant has now tweeted about it, I assume it’s OK to publicise. If you’re interested, feel free to leap in!

Wedel and Taylor 2013 bifurcation Figure 4 - classes of bifurcation

Figure 4. Cervical vertebrae of Camarasaurus supremus AMNH 5761 cervical series 1 in anterior view, showing different degrees of bifurcation of the neural spine. Modified from Osborn & Mook (1921: plate 67).

Today sees the publication of my big paper with Mike on neural spine bifurcation, which has been in the works since last April. It’s a free download here, and as usual we put the hi-res figures and other supporting info on a sidebar page.

Navel-gazing about the publication process

This paper is a departure for us, for several reasons.

For one thing, it’s a beast: a little over 13,000 words, not counting tables, figure captions, and the bibliography. I was all geared up to talk about how it’s my longest paper after the second Sauroposeidon paper (Wedel et al. 2000), but that’s not true. It’s my longest paper, period (13192 vs 12526 words), and the one with the most figures (25 vs 22).

It’s the first time we’ve written the paper in the open, on the blog, and then repackaged it for submission to a journal. I have several things to say about that. First, it was more work than I expected. It turns out that I definitely do have at least two “voices” as a writer, and the informal voice I used for the initial run of blog posts (linked here) was not going to cut it for formal publication. So although there is very little new material in the paper that was not in the blog posts, a lot of the prose is new because I had to rewrite almost the whole thing.

I have mixed feelings about this. On one hand, last May kinda sucked, because just about every minute that wasn’t spent eclipse chasing was spent rewriting the paper. On the other hand, as Mike has repeatedly pointed out to me, it was a pretty fast way to generate a big paper quickly, even with the rewriting. It was just over two months from the first post in the destined-to-become-a-paper series on April 5, to submission on June 14 (not June 24 as it says on the last page of the PDF), and if you leave out the 10 days in late May that I was galavanting around Arizona, the actual time spent working on the paper was a bit under two months. It would be nice to be that productive all the time (it helped that we were basically mining everything from previously published work; truly novel work usually needs more time to get up and going).

Wedel and Taylor 2013 bifurcation Figure 18 - Barosaurus and Supersaurus cervicals

Figure 18. Middle cervical vertebrae of Barosaurus AMNH 6341 (top) and Supersaurus BYU 9024 (bottom) in left lateral view, scaled to the same centrum length. The actual centrum lengths are 850 mm and 1380 mm, respectively. BYU 9024 is the longest single vertebra of any known animal.

You may fairly wonder why, if almost all the content was already available on the blog, we went to the trouble of publishing it in a journal. Especially in light of sentiments like this. For my part, it’s down to two things. First, to paraphrase C.S. Lewis, what I wrote in that post was a yell, not a thought. I never intended to stop publishing in journals, I was just frustrated that traditional journals do so many stupid things that actually hurt science, like rejecting papers because of anticipated sexiness or for other BS reasons, not publishing peer reviews, etc. Happily, now there are better options.

Second, although in a sane world the quality of an argument or hypothesis would matter more than its mode of distribution, that’s not the world we live in. We’re happy enough to cite blog posts, etc. (they’re better than pers. comms., at least), but not everyone is, and the minimum bound of What Counts is controlled by people at the other end of the Overton window. So, bottom line, people are at least theoretically free to ignore stuff that is only published on blogs or other informal venues (DML, forums, etc.). If you want to force someone to engage with your ideas, you have to publish them in journals (for now). So we did.

Finally, ever since Darren’s azhdarchids-were-storks post got turned into a paper, it has bothered me that there is an icon for “Blogging on Peer-Reviewed Research” (from ResearchBlogging.org), but not one (that I know of) for “Blogging Into Peer-Reviewed Research”. If you have some graphic design chops and 10 minutes to kill, you could do the world a favor by creating one.

Hey, you! Want a project?

One of the few things in the paper that is not in any of the blog posts is the table summarizing the skeletal fusions in a bunch of famous sauropod specimens, to show how little consistency there is:

Wedel and Taylor 2013 NSB Table 1 - sauropod skeletal fusions

(Yes, we know that table legends typically go above, not below; this is just how they roll at PJVP.)

I want this to not get overlooked just because it’s in a long paper on neural spine bifurcation; as far as I’m concerned, it’s the most important part of the paper. I didn’t know that these potential ontogenetic indicators were all mutually contradictory across taxa before I started this project. Not only is the order of skeletal fusions inconsistent among taxa, but it might also be inconsistent among individuals or populations, or at least that’s what the variation among the different specimens of Apatosaurus suggests.

This problem cries out for more attention. As we say at the end of the paper:

To some extent the field of sauropod paleobiology suffers from ‘monograph tunnel vision’, in which our knowledge of most taxa is derived from a handful of specimens described decades ago (e.g. Diplodocus carnegii CM 84/94). Recent work by McIntosh (2005), Upchurch et al. (2005), and Harris (2006a, b, c, 2007) is a welcome antidote to this malady, but several of the taxa discussed herein are represented by many more specimens that have not been adequately described or assessed. A comprehensive program to document skeletal fusions and body size in all known specimens of, say, Camarasaurus, or Diplodocus, could be undertaken for relatively little cost (other than travel expenses, and even these could be offset through collaboration) and would add immeasurably to our knowledge of sauropod ontogeny.

So if you’re looking for a project on sauropod paleobiology and you can get around to a bunch of museums*, here’s work that needs doing. Also, you’ll probably make lots of other publishable observations along the way.

* The more the better, but for Morrison taxa I would say minimally: Yale, AMNH, Carnegie, Cleveland Museum of Natural History, Field Museum, Dinosaur National Monument, BYU, University of Utah, and University of Wyoming, plus Smithsonian, University of Kansas, OMNH, Denver Museum, Wyoming Dinosaur Center, and a few others if you can swing it. Oh, and Diplodocus hayi down in Houston. Check John Foster’s and Jack McIntosh’s publications for lists of specimens–there are a LOT more out there than most people are familiar with.

References