Among the numerous weird features of MWC 8028, the Snowmass Haplocanthosaurus, is the extreme biconcave profile of the caudal vertebrae, in which each centrum is basically reduced to a vertical plate of bone separating two cup-shaped articular surfaces. All four available caudals — found in different parts of the quarry, in different orientations — have essentially the same cross-section. For the diagram above, I just copied caudal 3, because it’s the most complete, so I could figure out the thickness and cross-sectional shape of a single intervertebral disc.

I drew a more realistic version, with the first three caudals at approximately the right scale, for our neural canal paper last year:

The first three caudal vertebrae of Haplocanthosaurus specimen MWC 8028 in midsagittal section, emphasizing the volumes of the neural canal (yellow) and intervertebral joint spaces (blue). Anterior is to the right. Wedel et al. (2021: fig. 2B).

It’s a drawing, sure, but it’s based on a true story, because we have CT scans of all the vertebrae (and we’re going to publish them, soon, along with the reconstructed verts). 

(NB: I’m using “intervertebral disc” as a convenient shorthand for “whatever soft tissues filled the joint space”. But I do think it was a big, fat, fibrocartilaginous disc, not wildly different from the ones in the human vertebral column. It’s not totally impossible that there was some combination of crazy thick articular cartilage and a synovial cavity — there is some precedent in extant salamanders and lizards — but that seems way less likely, for reasons I’ll go into in detail elsewhere. Incidentally, the notion is floating around that reptiles have only synovial intervertebral joints, but this is simply false: intervertebral discs are present in some squamates [Winchester and Bellairs 1977] and in the tails of birds [Baumel 1988].)

I should point out that the other specimens of Haplocanthosaurus also have biconcave caudal vertebrae, but the concavities are much shallower. So what we’re seeing in MWC 8028 is an extreme version of something we see in other individuals of the same genus.

Now, because the caudal centra and joint spaces are roughly radially symmetrical, their relative cross-sectional areas, in these mid-sagittal sections, should be good proxies for their relative volumes. You can imagine the generating the volume of a centrum by rotating its cross-section through 180 degrees, ditto for the joint space (ignoring tilt since both the centrum and joint space are tilted). We’ll have this math worked out in more detail in the next paper, along with volumes from the 3D models, but the upshot is this:

The volume of the intervertebral discs is about twice that of the vertebral centra. If we ignore the neural arch and spine and the transverse processes, and focus only on the weight-bearing column formed by the proximal caudal centra and intervertebral discs, that column is 2/3 cartilage and only 1/3 bone. 

Why, tho?

I spent some time brainstorming with Alton Dooley and we came up with a whole slate of hypotheses. We don’t necessarily like any of them very much, we’re just trying to cast the widest possible net, to make sure we haven’t overlooked any possibilities, no matter how remote they might seem. Here’s what we have so far:

Non-biological:

1. taphonomic distortion

Abnormal biology:

2. congenital malformation

3. pathology

Ontogenetic:

4. incomplete ossification (animal died without laying down the ‘missing’ bone)

5. senescence (the ‘missing’ bone was removed by some process related to aging)

Functional:

6. increased or decreased movement between vertebrae

7. weight reduction

8. shock absorption

What else? 

To reiterate, we’re in the hypothesis-generating stage, not the hypothesis-evaluating stage. So we’re not interested in whether any of these hypotheses are likely. (In point of fact, I think the ones we have so far all suck.) We just want all of the ideas that aren’t impossible.

The comment field is open!

References

• Baumel, J.J. 1988. Functional morphology of the tail apparatus of the pigeon (Columba livia). Advances in Anatomy, Embryology, and Cell Biology 110: 1-115.
• Wedel, Mathew; Atterholt, Jessie; Dooley, Jr., Alton C.; Farooq, Saad; Macalino, Jeff; Nalley, Thierra K.; Wisser, Gary; and Yasmer, John. 2021. Expanded neural canals in the caudal vertebrae of a specimen of Haplocanthosaurus. Academia Letters, Article 911, 10pp.
• Winchester, L. and Bellairs, A.D.A. 1977. Aspects of vertebral development in lizards and snakes. Journal of Zoology 181(4): 495-525.

This is the first 3D print of a dinosaur bone that I ever had access to: the third caudal vertebra of MWC 8028, the ‘new’ Haplocanthosaurus specimen from Snowmass, Colorado (Foster and Wedel 2014, Wedel et al. 2021). I’ve been carrying this thing around since 2018. It’s been an aid to thought. I touched on this before, in this post, but real sauropod vertebrae are almost always a giant pain to work with, given their charming combination of great weight, fragility, and irreplaceability. As opposed to scaled 3D prints, which are light, tough, and endlessly replaceable.

This was brought home to me again a couple of weeks ago, when I visited the Carnegie Museum, in Pittsburgh, Pennsylvania, and Research Casting International, in Trenton, Ontario, Canada. I was at each place to have another look at their haplocanthosaur specimens. The Carnegie is of course the home of CM 572, the type of H. priscus, and CM 879, the type of H. utterbacki (which has long been sunk into H. priscus, and rightly so — more on that another time, perhaps). RCI currently has CMNH 10380, the holotype of H. delfsi, for reprepping and remounting before it goes back to the Cleveland Museum of Natural History.

Caudals 1 through 6 of CM 572, the holotype of Haplocanthosaurus priscus.

The caudals of CM 572 and CM 879 aren’t that different in size — the centra max out at about 20cm (8in) in diameter, and the biggest, caudal 1 of CM 572, is 50cm (20in) tall. Still, given their weight and the number of thin projecting processes that could possibly break off, I handled them gingerly.

Caudals 1 through 5 of CM 10380, the holotype of Haplocanthosaurus delfsi.

The caudals of H. delfsi are a whole other kettle of fish. Caudal 1 has a max diameter of 36cm (14in) and a total height of 85cm (33.5in). I didn’t handle that one by myself unless I absolutely had to. Fortunately Garth Dallman of RCI helped a lot with the very literal heavy lifting, as did fellow researcher Brian Curtice, who was there at the same time I was.

Back to my beloved MWC 8028, the Snowmass haplocanthosaur. My colleagues and I are still working on it, and there will be more papers coming down the pike in due time (f’rinstance). I’m pretty sure that the main reason we’ve been able to get so much mileage out of this mostly incomplete and somewhat roadkilled specimen is that we’ve had 3D prints of key bones to play with. Now, I joke all the time about being a grownup who gets paid to play with dinosaur bones, but for once I’m not writing in jest when I say ‘play with’. That 3D printed caudal is basically a dinosaurian fidget toy for me, and I think it’s probably impossible to play with anatomical specimens without getting interested in their nooks and crannies and bits and bobs.

Another nice thing about it: I can throw it in my luggage, take it Oklahoma or Utah or Pennsylvania or Canada, and just plop it in someone’s hand and say, “Look at this weird thing. Have you ever seen that before?” I have done that, in all of those places, and it’s even more convenient and useful than showing CT slices on my laptop. I’ve watched my friends and colleagues run their fingers over the print, pinch its nearly non-existent centrum, poke at its weird neural canal, and really grokk its unusual morphology. And then we’ve had more productive conversations than we would have otherwise — they really Get It, because they’ve really handled it.

When I started writing this post, the title was a question, but that’s tentative to the point of being misleading. Three-D prints are obviously useful for sauropod workers because with very few exceptions our specimens are otherwise un-play-with-able. And playing with dinosaur bones turns out to be a pretty great way to make discoveries, and to share them.

(And yes, we’ll be publishing the CT scans and 3D models of MWC 8028 in due time, so you can play with it yourself.)

References

• Foster, J.R., and Wedel, M.J. 2014. Haplocanthosaurus (Saurischia: Sauropoda) from the lower Morrison Formation (Upper Jurassic) near Snowmass, Colorado. Volumina Jurassica 12(2): 197–210. DOI: 10.5604/17313708 .1130144
• Wedel, Mathew; Atterholt, Jessie; Dooley, Jr., Alton C.; Farooq, Saad; Macalino, Jeff; Nalley, Thierra K.; Wisser, Gary; and Yasmer, John. 2021. Expanded neural canals in the caudal vertebrae of a specimen of Haplocanthosaurus. Academia Letters, Article 911, 10pp. DOI: 10.20935/AL911

Vertebrae of Haplocanthosaurus (A-C) and a giraffe (D-F) illustrating three ways of orienting a vertebra: articular surfaces vertical — or at least the caudal articular surface vertical (A and D), floor of the neural canal horizontal (B and E), and similarity in articulation (C and F). See the paper for details! Taylor and Wedel (2002: fig. 6).

This is a lovely cosmic alignment: right after the 15th anniversary of this blog, Mike and I have our 11th coauthored publication (not counting abstracts and preprints) out today.

Taylor, Michael P., and Wedel, Mathew J. 2022. What do we mean by the directions “cranial” and “caudal” on a vertebra? Journal of Paleontological Techniques 25:1-24.

This one started back in 2018, with Mike’s post, What does it mean for a vertebra to be “horizontal”? That post and subsequent posts on the same topic (one, two, three) provoked interesting discussions in the comment threads, and convinced us that there was something here worth grappling with. We gave a presentation on the topic at the 1st Palaeontological Virtual Congress that December, which we made available as a preprint, which led to us writing the paper in the open, which led to another preprint (of the paper this time, not the talk).

Orienting vertebrae with the long axis of the centrum held horizontally seems simple enough, but choosing landmarks can be surprisingly complex. Taylor and Wedel (2022 fig. 5).

This project represented some interesting watersheds for us. It was not our first time turning a series of blog posts into a paper — see our 2013 paper on neural spine bifurcation for that — but it was our first time writing a joint paper in the open (Mike had started writing the Archbishop description in the open a few months earlier). It was also the last, or at least the most recent, manuscript that we released as a preprint, although we’ve released some conference presentations as preprints since then. I’m much less interested in preprints than I used to be, for reasons explained in this post, and I think Mike sees them as rather pointless if you’re writing the paper in the open anyway, which is his standard approach these days (Mike, feel free to correct me here or in the comments if I’m mischaracterizing your position).

So, we got it submitted, we got reviews, and then…we sat on them for a while. We have both struggled in the last few years with Getting Things Done, or at least Getting Things Finished (Mike’s account, my own), and this paper suffered from that. Part of the problem is that Mike and have far too many projects going at any one time. At last count, we have about 20 joint projects in various stages of gestation, and about 11 more that we’ve admitted we’re never going to get to (our To Don’t list), and that doesn’t count our collaborations with others (like the dozen or so papers I have planned with Jessie Atterholt). We simply can’t keep so many plates spinning, and we’re both working hard at pruning our project list and saying ‘no’ to new things — or, if we do think of new projects, we try to hand them off to others as quickly and cleanly as possible.

Two different ways of looking at a Haplocanthosaurus tail vertebra. Read on for a couple of recent real-life examples. Taylor and Wedel (2022: fig. 2).

Anyway, Mike got rolling on the revisions a few months ago, and it was accepted for publication sometime in late spring or early summer, I think. Normally it would have been published in days, but the Journal of Paleontological Techniques was moving between websites and servers, and that took a while. But Mike and I were in no tearing rush, and the paper is out today, so all is well.

One of the bits of the paper that I’m most proud of is the description of cheap and easy methods for determining the orientation of the neural canal. For neural canals that are open, either because they were fully prepped or never full of matrix to begin with, there’s the rolled-up-piece-of-paper method, which I believe first appeared on the blog back when I was posting photos of the tail vertebrae of the Brachiosaurus altithorax holotype. For neural canals that aren’t open, Mike came up with the Blu-tack-and-toothpick method, as shown in Figure 12 in the new paper:

A 3d print of NHMUK PV R2095, the holotype of Xenoposeidon, illustrating the toothpick method of determining neural canal orientation. Taylor and Wedel (2022: fig. 12).

I know both methods work because I recently had occasion to use them, studying the Haplocanthosaurus holotypes (see this post). For CM 572, the neural canal of the first caudal vertebra is full of matrix, so I used a variant of the toothpick method. I didn’t actually have Blu-tack or toothpicks, so I cut thin pieces of plastic from the edge of an SVP scale bar and stuck them in bits of kneadable eraser. It worked just fine:

The neural canal of caudal 2 was prepped, so I could use the rolled-up-piece-of-paper method:

(Incidentally, Mike and I refer to our low-tech orientation-visualizers as “neural-canal-inators”, in honor of Dr. Heinz Doofenshmirtz from Phineas and Ferb.)

In the above photos, notice how terribly thin the base of the neural arch is, antero-posteriorly. Both of these vertebrae are in pretty good shape, without much breakage or missing material, and their morphology is broadly consistent with that of other proximal caudals of Haplocanthosaurus, so we can’t write this off as distortion. As weird as it looks, this is just what Haplo proximal caudals were like. And with the neural canals held horizontally, the first two caudals end up oriented like so:

Now, as we pointed out in the paper, the titular question is not about determining the posture of the vertebrae in life, it’s about defining the directions ‘cranial’ and ‘caudal’ for isolated vertebrae — Mike asked the question back when for the holotype (single) dorsal vertebra of Xenoposeidon. But an interesting spin-off for me has been getting confronted with the weirdness of vertebrae whose articular surfaces are nowhere near orthogonal with their neural canals. I tilted those CM 572 Haplo caudals so that their neural canals were horizontal partly because that’s the preferred orientation that Mike and I landed on in the course of this work, but also partly because to me, that’s a more arresting image than the preceding ones with the articular faces held vertically. I’m both freaked out and fascinated, and that seems like a promising combination — there are mysteries here that cry out to be solved.

As usual, we have loads of people to thank. In addition to all those listed in the Acknowledgments of the new paper, I’m grateful to Matt Lamanna and Amy Henrici of the Carnegie Museum of Natural History for letting me play with study the Haplo specimens in their care. Mike and I also owe a huge thanks to the editorial team at the Journal of Paleontological Techniques. We reached out to them a few days ago to ask if it might be possible to get our in-press paper done and out in time for SV-POW!’s anniversary weekend, and they pitched in to make it happen.

What’s next? We weighed the evidence and formulated what the best solution we could think of. Now it’s up to the world to decide if that was a useful contribution. The comment thread is open — let’s find out.

Long-time readers will recall that I’m fascinated by neurocentral joints, and not merely that they exist (although they are pretty cool), but that in some vertebrae they migrate dorsally or ventrally from their typical position (see this and this).

A few years ago I learned that there is a term for the expanded bit of neural arch pedicle that contributes to the centrum in vertebrae with ventrally-migrated neurocentral joints: the bouton, which is French for ‘button’. Here’s an example in the unfused C7 of a subadult sheep. Somebody gifted me a handful of these things a few years ago, and I’ve been meaning to blog about them forever. Many thanks, mysterious benefactor. (I mean, only mysterious to me, because my memory is crap; I’m sure you know who you are, and if you ever read this, feel free to remind me. And thanks for the dead animal parts!)

Guess what? You have these things, too! Or at least you did; if you’re old enough to be reading this, your boutons fused with the rest of the separate bits of your vertebrae a long time ago, between the ages of 2 and 5 (according to Bagnall et al. 1977). Here’s a diagram from Schaefer et al. (2009: p.99) showing the separate centrum and neural arch elements in a thoracic vertebra of a human toddler. So, hey, cool, we all had boutons, just like sheep. And just like some sauropods. (You didn’t think I was going to do a whole OVATOD post without sauropods, did you?)

Here’s our old friend BIBE 45885, an unfused caudal neural arch (or perhaps neural ring) of Alamosaurus, which I’ve been freaking out over for five years now. Those fat bits of neural arch that very nearly close off the neural canal ventrally? Boutons, baby! Big, beautiful boutons. In this photo it looks like the paired boutons meet on the midline, but in fact they merely overlap from this point of view — there is a narrow (<1mm) squiggly gap between them. Given how narrow that gap is, I suspect the two boutons probably would have fused to each other before either of them fused to the centrum, if this particular animal hadn’t died first.

Here’s an unfused dorsal centrum of Giraffatitan, MB.R. 3823, which I yapped about in this post. This vertebra is the spiritual opposite of the Alamosaurus caudal shown above: instead of the neural canal being nearly enclosed by bits of the neural arch wrapping around ventrally, the neural canal is nearly enclosed dorsally by bits of the centrum sticking up on either side and wrapping around dorsally. As with the boutons of the Alamosaurus caudal, the two expanded bits of centrum stuff in this Giraffatitan dorsal approach each other very closely but don’t quite meet; you can fit a piece of paper between them, but not a heck of a lot more. In essence, those “two expanded bits of centrum stuff” are centrum boutons that project up into what I suppose we’ll keep calling a ‘neural arch’ even though it’s neither very neural nor an arch. Or perhaps anti-boutons? With apologies to Gould and Vrba (1982), here we have another missing term in the science of form.

Why do we, and sheep, and prolly lots of other mammals, and some sauropods, have boutons? Presumably to strengthen the neurocentral joints by expanding the joint surface area. I don’t know if anyone has ever tested that — if you do, please let me know in the comments.

Many thanks to Thierra Nalley, who may be the only person I know besides Mike who spends more time thinking about vertebrae than I do, for introducing me to the term ’bouton’ a few years ago. If for some reason you want to corrupt your sensibilities reading about primate vertebrae, you could do a lot worse than checking out Thierra’s papers.

I don’t expect we’ll have a ton of OVATOD posts, in part because there aren’t a heck of a lot of vertebra parts that we haven’t already blogged about. But who knows, maybe Mike will write about prepostepipophyses or something. Stay tuned!

References

• Bagnall, K.M., Harris, P.F., and Jones, P.R.M. 1977. A radiographic study of the human fetal spine. 2. The sequence of development of ossification centers in the vertebral column. Journal of Anatomy 124(3): 791–802.
• Gould, S.J. and Vrba, E.S. 1982. Exaptation—a missing term in the science of form. Paleobiology 8(1): 4-15.
• Schaefer, M., Black, S., and Scheuer, L. 2009. Juvenile Osteology: A Laboratory and Field Manual. Academic Press, Burlington, MA, 369pp.

P.S. Can we all pitch in and make ’bouton’ the new ‘aglet‘? Please? Please?

Over on Mastodon (sign up, it’s great!), Jim Kirkland posted a baby Utahraptor caudal vertebrae for #FossilFriday. Here it is:

And after a bit of virtual prep work:

My first reaction was just “That’s pretty!“. My second, which I admit should have been my first, was “Wait a sec — how the heck do those things articulate?”

The issue is that both the prezygs and the postzygs overhang the centrum by so much. If we imagine three of these babies consecutively, there are basically two options.

First, the centra articulate closely, with what we might feel intuitively is a reasonable cartilage gap; and the zygs cross over:

Does something like this ever happen? Not in sauropods, for sure, but it could be correct — if the zyg facets are some way short of the tips of their processes, so that the most distal parts of each process are pre-epipophyses and epipophyses rather than prezygs and postzygs per se.

The other interpretation is this, with the zygs overlapping near the end as in sensible dinosaurs, and much more spaced out centra:

If this is right, then (in this respect) baby Utahraptor tails resembled camel necks in having big intervertebral spaces, which in life were filled with big cartilage plugs.

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SPOILER SPACE

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Have a think about this before reading on.

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SPOILER SPACE

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OK, here is the horrible truth.

Dromaeosaur tails do overlap their zyg processes as in the first mock-up above: but they do much, much worse than this!

Here is the truly perverted figure 37 of Ostrom’s classic 1969 monograph on Deinonychus — the publication that catalysed the whole Dinosaur Renaissance:

As you can see, the zygapophyseal processes are grotesquely elongated, and overlap in long stiffening bundles with those of successive vertebrae (part C of the figure). The actual zyg facets are small, and close to the origins of these processes (see parts A and B of the figure). And the chevrons are also hideously protracted beyond their natural length to form stiffening bundles beneath the tail that complement those above the tail.

To add insult to injury, the chevrons even face in the wrong darned direction, extending anteriorly along the tail rather than posteriorly as in all decent animals. Yes: in Ostrom’s illustrations, we’re seeing the vertebrae in right lateral view, i.e. anterior is to the right.

All of this confirms that I was so, so right two decades ago to focus so completely on proper dinosaurs instead of these nasty mutant ones. Ugh.

Michelle Stocker with an apatosaur vertebra (left) and a titanosaur femur (right), both made from foam core board.

In the last post I showed the Brachiosaurus humerus standee I made last weekend, and I said that the idea had been “a gleam in my eye for a long time”. That’s true, but it got kicked into high gear late in 2021 when I got an email from a colleague, Dr. Michelle Stocker at Virginia Tech. She wanted to know if I had any images of big sauropod bones that she could print at life size and mount to foam core board, to demonstrate the size of big sauropods to the students in her Age of Dinosaurs course. We had a nice conversation, swapped some image files, and then I got busy with teaching and kinda lost the plot. I got back to Michelle a couple of days ago to tell her about my Brach standee, and she sent the above photo, which I’m posting here with her permission.

That’s OMNH 1670, a dorsal vertebra of the giant Oklahoma apatosaurine and a frequent guest here at SV-POW!, and MPEF-PV 3400/27, the right femur of the giant titanosaur Patogotitan, from Otero et al. (2020: fig. 8). (Incidentally, that femur is 236cm [7 feet, 9 inches] long, or 35cm longer than our brachiosaur humerus.) For this project Michelle vectorized the images so they wouldn’t look low-res, and she used 0.5-inch foam core board. She’s been using both standees in her Age of Dinosaurs class at VT (GEOS 1054) every fall semester, and she says they’re a lot of fun at outreach events. You can keep up with Michelle and the rest of the VT Paleobiology & Geobiology lab group at their research page, and follow them @VTechmeetsPaleo on Twitter.

Michelle’s standees are fully rad, and naturally I’m both jealous and desirous of making my own. I’ve been wanting a plywood version of OMNH 1670 forever. If I attempt a Patagotitan femur, I’ll probably follow Michelle’s lead and use foam core board instead of plywood — the plywood Brach humerus already gets heavy on a long trek from the house or the vehicle.

Speaking of, one thing to think about if you decide to go for a truly prodigious bone is how you’ll transport it. I can haul the Brach humerus standee in my Kia Sorento, but I have to fold down the middle seats and either angle it across the back standing on edge, or scoot the passenger seat all the way forward so I can lay it down flat. I could *maybe* get the Patagotitan femur in, but it would have to go across the tops of the passenger seats and it would probably rest against the windshield.

Thierra Nalley and me with tail vertebrae of Haplocanthosaurus (smol) and the giant Oklahoma apatosaur (ginormous), at the Tiny Titan exhibit opening.

As long as I’m talking about cool stuff other people have built, a formative forerunner of my project was the poster Alton Dooley made for the Western Science Center’s Tiny Titan exhibit, which features a Brontosaurus vertebra from Ostrom & McIntosh (1966) blown up to size of OMNH 1331, the largest centrum of the giant Oklahoma apatosaurine (or any known apatosaurine). I wouldn’t mind having one of those incarnated in plywood, either.

I’ll bet more things like this exist in the world. If you know of one — or better yet, if you’ve built one — I’d love to hear about it.

References

• Alejandro Otero , José L. Carballido & Agustín Pérez Moreno. 2020. The appendicular osteology of Patagotitan mayorum (Dinosauria, Sauropoda). Journal of Vertebrate Paleontology, DOI: 10.1080/02724634.2020.1793158
• Ostrom, John H., and John S. McIntosh. 1966. Marsh’s Dinosaurs. Yale University Press, New Haven and London. 388 pages including 65 absurdly beautiful plates.

This is one of those posts where the title pretty much says it all, but here’s the detailed version.

Recap: the 2013 paper

In Matt’s and my 2013 paper Caudal pneumaticity and pneumatic hiatuses in the sauropod dinosaurs Giraffatitan and Apatosaurus (Wedel and Taylor 2013b), we wrote about the Brontosaurus excelsus holotype 1980:

Much more convincing, however, are two isolated lateral fossae: one on the left side of caudal 9, the other on the right side of caudal 13 (Figure 10). Both of these are much larger than the aforementioned foramina – about 6 cm across – and have distinct lips. There is absolutely no trace of similar fossae in any of the other caudals, so these fossae represent a bilateral pneumatic hiatus of at least seven vertebrae

And we illustrated the right side of Ca13 in our figure 10:

Wedel and Taylor (2013:figure 10). An isolated pneumatic fossa is present on the right side of caudal vertebra 13 in Apatosaurus excelsus holotype YPM 1980. The front of the vertebra and the fossa are reconstructed, but enough of the original fossil is visible to show that the feature is genuine.

Fast forward to 2023

The Yale Brontosaurus has been dismounted and sent to RCI in Canada for some long overdue TLC. It’s being re-prepared, and Brian Curtice has seen the material close up. The news from Brian is not good: I quote some of his emails. First, on 26 January:

The 1980 caudal 13 it isn’t pneumatic. That whole hole is plaster. The 2 verts in front of it have similar damage but on the opposite side. It looks like they were damaged during preservation, excavation, or preparation.

Then on 27 January:

Quick caudal pneumatic update: other than the fact 1980 has a large number of what I dub nutrient foramina there isn’t any shiny surfaces, no odd sculpting, fluting, etc. the bone is exquisite in these areas but will soon be painted black.

Later that day:

It was also exceptionally difficult to sometimes tell what was actual bone. Barbour [1890 — ed.] is spot on at what Marsh had done. The preparators sometimes couldn’t be sure without acetone and an air scribe… I did the best I could but my goodness it was tough and may have errors. Thus I stayed towards what I was positive on.

On 3 February, I wrote back to Brian asking:

My question about the “pneumatic fossa” in caudal 13 is: why did they sculpt it like that? It would have been the simplest thing in the world to give it a simple flat lateral aspect, like the other caudals, so what made them put the fossa in? One possible answer is that that’s what the bone was actually like, but smashed up, and they “repaired” it. I guess we are unlikely ever to know.

He replied the same day:

There are 3 caudals (11-13, pics attached) with similarly damaged bone, punky and smashed and “beat up”, with 11 and 12 having the damage on the left and ventral and 13 on the right. I suspect they were lying close to one another. I couldn’t tell if it was trampling, but it didn’t seem like it was from being hacked from the ground.
[…]
As to why they did it? I suspect because 13’s damage wasn’t as jagged, they could plaster over it easier? We’ll never know for sure.

Brian sent a photo of the re-prepared caudal 13, showing … well, see for yourself:

Truthfully, I don’t find this especially compelling. But that’s about the inadequacy of photos for this kind of work. My inclination is to trust Brian’s interpretation, while wondering how Matt and I were both fooled back in June 2012 when we visited YPM together and spent significant time gazing at this caudal.

So what now?

The good news for us is that this doesn’t really change any of our arguments or conclusion in the 2013 paper. We said that there is previously undocumented evidence of caudal pneumaticity in apatosaurines[1] — and there still is, in the other specimen we figured, FMNH P25112, in our figure 9. And the significant conclusion of the papers was the intermittent and unpredictable pneumatization along the tails of sauropods is compelling evidence for extensive “cryptic pneumaticity” — that is, for soft-tissue pneumatization alongside vertebrae that did not penetrate the bone. That conclusion is still good.

But still: one of the data-points we relied on in making that argument no longer looks solid, and it feels like the honest thing is to document that. It probably doesn’t warrant a follow-up paper or even an erratum. But it does warrant a blog-post, and this is it.

Thanks to Brian for bringing it to our attention!

Notes

[1]. In the paper we said “in Apatosaurus“, not “in apatosaurines”. But that was back when Apatosaurus was the only recognized apatosaurine, so it amounted t0 the same thing. If we were writing it in the post-Tschopp-et-al. world of today, we’d say “in apatosaurines”.

References

• Barbour, Erwin H. 1890. Scientific News: 5. Notes on the Paleontological Laboratory of the United States Geological Survey under Professor Marsh. The American Naturalist 24(280): 388-400.
• Wedel, Mathew J., and Michael P. Taylor. 2013. Caudal pneumaticity and pneumatic hiatuses in the sauropod dinosaurs Giraffatitan and Apatosaurus.PLOS ONE 8(10):e78213. 14 pages. doi:10.1371/journal.pone.0078213 [PDF]

Sauropod vertebrae in anterior view exhibiting a spectrum of variation in the dorsoventral positions of the neurocentral joint. Wedel and Atterholt (2023: fig. 1).

As described in the last post, Jessie Atterholt is presenting our poster on this project today, at the 14th Symposium on Mesozoic Terrestrial Ecosystems and Biota (MTE14) in Salt Lake City, and the related paper is in the MTE14 volume in The Anatomical Record. Here’s the citation and a direct link to the paper:

Wedel, M.J., and Atterholt, J. 2023. Expanded neurocentral joints in the vertebrae of sauropod dinosaurs. In Hunt-Foster, R.K., Kirkland, J.I., and Loewen, M.A. (eds), 14th Symposium on Mesozoic Terrestrial Ecosystems and Biota. The Anatomical Record 306(S1):256-257.

I’ve been interested in neurocentral fusion in sauropods and other critters for a long time, especially when the neurocentral joint is shifted dorsally or ventrally relative to the neural canal. I noted some instances of those shifted joints in blog posts (one, two, three), but I didn’t know what to do with that information. The impetus to turn those observations into a paper came from two sources. First, working with Jessie got me thinking about shifted neurocentral joints as one more Batman villain in the rogue’s gallery of neural-canal-related weirdness in birds, sauropods, and other archosaurs. Jessie and I kindled the ambition to catalog that entire zoo — results of that mega-project so far are on a new sidebar page. 

Fronimos and Wilson (2017: figure 2)

Second, I read Fronimos and Wilson (2017). This is an extremely cool paper and it’s a shame I haven’t blogged about it before. The authors went through the cervical and dorsal vertebrae of the holotype skeleton of Spinophorosaurus (GCP-CV-4229) and measured the complexity of the neurocentral joints. They found that joint complexity increased toward the base of the neck, maxed out in the anterior dorsals, and decreased in posterior dorsals. That’s consistent with the idea that complex neurocentral joints were an adaptation to increasing biomechanical stress on the vertebrae, which should likewise increase toward the base of the long, cantilevered neck and decrease toward the big anchor of the sacrum. The basic idea is that the complex joints increased the joint surface area and decreased the likelihood of traumatic dislocations — disrupting the joint between the arch and centrum would tend to cause life-ending spinal cord injuries.

Available surface area for the neurocentral joint in its normal position (below) and shifted dorsally, above the neural canal (above). The lower part of the neural arch is H-shaped in cross-section, with anterior and posterior fossae below the zygapophyses. The real-life example this is based on is in the last image in this post.

Reading that paper was a lightbulb moment for me. If the neurocentral joints of sauropods were adapted to resist biomechanical stresses, anything that increased the “contact patch” between neural arch and centrum would be desirable. From the standpoint of a neural arch and centrum trying to stick together, the neural canal is a flaw, a big dumb area of forced non-union. But you can’t get rid of the neural canal, which houses the spinal cord and the developmentally important spinal arteries (see Taylor and Wedel 2021 for more on the latter). The only way to eliminate the gap caused by the neural canal is to get around it by shifting the neurocentral joint dorsally or ventrally. John Gilmore famously said that the internet interprets censorship as damage and routes around it. We hypothesize that in an evolutionary sense, sauropod neurocentral joints interpreted the neural canal as damage and routed around it.

Of course you don’t have to be a sauropod to benefit from the enlarged contact patch between neural arch and centrum, as shown by the ’boutons’ of many mammals, including humans (unfused sheep vertebra shown above). But as Fronimos and Wilson (2017) pointed out, strengthening the neurocentral joints was probably especially important for sauropods, which grew rapidly for a long time and achieved large body size with many joints still unfused (see also Wedel and Taylor 2013: table 1, Hone et al. 2016: table 2). That would also explain why some sauropods went well beyond bouton territory, into having the neurocentral joint entirely dorsal or ventral to the canal.

Hey, it only took me five and a half years to get this idea out of my notebook and into a peer-reviewed paper!

There’s still the question of why the neurocentral joints shifted dorsally in some vertebrae and ventrally in others. The ventral shift in caudal vertebrae makes intuitive sense — the neural arch narrows dorsally, so shifting the joint upward would decrease the surface area, not increase it. Also, shifting the joint ventrally allowed the neural arch to be morticed between the transverse processes, which further increased the contact patch and made the neurocentral joint even stronger.

MB.R.3823, a dorsal centrum of Giraffatitan in posterodorsal view. The neurocentral joint surfaces of the centrum come together dorsal to the neural canal, leaving only a paper-thin gap.

What about dorsal vertebrae? In dorsal vertebrae of Haplocanthosaurus, Camarasaurus, and Giraffatitan, the neurocentral joint is shifted dorsally, to the point that in some Camarasaurus dorsals the joint lies completely above the neural canal. It’s not obvious why that would be more advantageous than shifting ventrally — except possibly that shifting ventrally might have interfered with pneumatization. In some unfused Cam dorsals, like the one shown below, the lateral pneumatic cavities are so big that they excavate right up under the dorsally-shifted neurocentral joint.

MWC 3630, an unfused dorsal centrum of Camarasaurus in right lateral (top) and posterior (bottom) views.

Still, pneumatic diverticula are thought to opportunistically occupy spaces that aren’t being loaded very much (Witmer 1997), so presumably they could make cavities above, below, or in any other direction from the neurocentral joint. We’re not really sure why the joint shifted dorsally in dorsal vertebrae of some sauropods. We know that the developmental program could accommodate shifts in both directions over fairly short distances in the same individual, because in the CM 879 skeleton of Haplocanthosaurus, the neurocentral joints are almost entirely above the neural canals in the dorsal vertebrae, and completely below the canals in the caudals. (The sacrals in that specimen are doing their own weird thing, about which more another time.)

DINO 4970, an unfused neural arch of Camarasaurus in the Carnegie Quarry (“the Wall”) at Dinosaur National Monument. The arch is in ventral view, with anterior toward the top. Note the butterfly-shaped neurocentral joint, with no gap for the neural canal.

Our paper is short and to the point because we don’t have a lot of data on this yet. Our sampling so far is basically limited to stuff we’ve stumbled over that made us go ‘huh!’ As with our work on paramedullary diverticula in birds, we hope that our work inspires more people to look into this weird stuff and document it — we can’t be sure about the rules until we know what all is out there.

References

• Fronimos, J.A. and Wilson, J.A., 2017. Neurocentral suture complexity and stress distribution in the vertebral column of a sauropod dinosaur. Ameghiniana, 54(1), pp.36-49.
• Hone, D.W.E., Farke, A.A., and Wedel, M.J. 2016. Ontogeny and the fossil record: what, if anything, is an adult dinosaur? Biology Letters 2016 12 20150947; DOI: 10.1098/rsbl.2015.0947.
• Taylor, Michael P., and Mathew J. Wedel. 2021. Why is vertebral pneumaticity in sauropod dinosaurs so variable? Qeios 1G6J3Q. doi:10.32388/1G6J3Q
• Wedel, Mathew J., and Michael P. Taylor. 2013. Neural spine bifurcation in sauropod dinosaurs of the Morrison Formation: ontogenetic and phylogenetic implications. Palarch’s Journal of Vertebrate Palaeontology 10(1):1-34. ISSN 1567-2158.
• Witmer, L.M. 1997. The evolution of the antorbital cavity of archosaurs: a study in soft-tissue reconstruction in the fossil record with an analysis of the function of pneumaticity. Journal of Vertebrate Paleontology 17(Supplement 1): 1-76.

Fig. 2. Rebbachisauridae indet. (MDPA-Pv 007) from the Sierra Chata locality (Candeleros Formation) Cenomanian (Upper Cretaceous). Anterior caudal vertebra in anterior (A1, A3), posterior (A4, A6), and left lateral (A7, A9) views. Close ups showing lateral spinal laminae (A2), accessory bony lamina located inside of spof (A5), foramina in the lateral surface of the centrum, arrowheads indicate the presence of foramina (A8). Abbreviations: acdl, anterior centrodiapophyseal lamina; amedl, anterior medial lamina; cdf, centrodiapophyseal fossa; cpol, centropostzygapophyseal lamina; cprl, centroprezygapophyseal laminae; nc, neural canal; pcdl, posterior centrodiapophyseal lamina; pmedl, posterior medial lamina; pocdf, postzygapophyseal centrodiapophyseal fossa; pocdf-l, postzygapophyseal centrodiapophyseal fossa lamina; posdf, postzygapophyseal spinodiapophyseal fossa; prcdf, prezygapophyseal centrodiapophyseal fossa; prcdf-l, prezygapophyseal centrodiapophyseal fossa lamina; prdl, prezygodiapophyseal lamina; prsdf, prezygapophyseal spinodiapophyseal fossa; pz, postzygapophyses; spof, spinopostzygapophyseal fossa; spdl, spinodiapophyseal lamina; spol-f, spinopostzygapophyseal lamina fossa; sprl, spinoprezygapophyseal laminae; sprl-f, spinoprezygapophyseal lamina fossa. Windholz et al. (2024: fig. 2).

I have a new paper out in Acta Paleontologica Polonica, with Guillermo Windholz, Juan Porfiri, Domenica Dos Santos, and Flavio Bellardini, on the first CT scan of a pneumatic caudal vertebra of a rebbachisaurid:

Windholz, G.J., Porfiri, J.D., Dos Santos, D., Bellardini, F., and Wedel, M.J. 2024. A well-preserved vertebra provides new insights into rebbachisaurid sauropod caudal anatomical and pneumatic features. Acta Palaeontologica Polonica 69(1):39-47. doi: 10.4202/app.01104.2023

This will be a short post because I’m on the road right now, but I’m pretty darned happy about this paper. Like many of my recent publications, this is primarily a descriptive paper, but with interesting implications.

Drawings of an Isle of Wight rebbachisaurid anterior caudal vertebra (MIWG 5384). A, anterior view; B, right lateral view; C, posterior view. Scale bar represents 200 mm. Mannion et al. (2011: fig. 2).

I’ve been interested in caudal pneumaticity in rebbachisaurids for a long time. As far as I can remember, the first paper that clued me in on the subject was Mannion et al. (2011), on Early Cretaceous rebbachisaurid material from the Isle of Wight. The deep, subdivided, often asymmetric fossae on the neural spines and transverse processes showed that at least some rebbachisaurids evolved caudal pneumaticity comparable to that of diplodocids. I’ve been wanting to see CT scans of a rebbachisaurid caudal ever since, and last summer, Guillermo Windholz wrote to offer me that very opportunity.

Fig. 4. Selected computed tomographic sections of Rebbachisauridae indet. (MDPA-Pv 007) from the Sierra Chata locality (Candeleros Formation) Cenomanian (Upper Cretaceous). Vertebra in anterior view (A1), transverse section taken at mid-length of the element (A2), parasagittal section (A3), frontal sections (A4–A10). Abbreviations: cdf, centrodiapophyseal fossa; nc, neural canal; pocdf, postzygapophyseal centrodiapophyseal fossa; prcdf, prezygapophyseal centrodiapophyseal fossa; spol-f, spinopostzygapophyseal lamina fossa; sprl-f, spinoprezygapophyseal lamina fossa. Windholz et al. (2024: fig. 4).

The scans are beautiful, but the revealed anatomy is wacky. The neural spine and transverse processes are shown to be formed of thin, intersecting laminae that bound deep fossae, which is always cool to see but also expected at this point — Osborn figured similarly-excavated neural spine cross-sections from Diplodocus back in 1899. Internally, the centrum shows a network of large, interconnected chambers, but the internal structure is wildly asymmetric. This is particularly evident in parts A2 and A10 of Figure 4, shown above.

So what’s going on here? Why is pneumatization of the neural spine and transverse processes so complete, while pneumatization of the centrum is so haphazard? I’m a big fan of asymmetric pneumatization, but this is ridiculous. And the bottom half of the centrum is basically a brick, in stark contrast to the extensive pneumatization of the upper works. I have some thoughts on this, but they’ll keep for a future post.

Also worth noting: although CT scanning fossils is becoming so common that it’s almost de rigueur these days, our global pool of CT-scanned sauropod vertebrae is tiny. Most of what we think we know — what I think I know, what I’ve built a good chunk of my career on — is connecting some very widely-spaced dots. Until last year, in all of human history we’d not managed to scan a single pneumatic caudal of a rebbachisaurid. Now we’ve scanned exactly one — which AFAIK is one more than the number of scanned vertebrae of any kind from Barosaurus, to pick an example at random. I wonder how much we’ll have learned when that number (in either category, Barosaurus vertebrae or rebbachisaurid caudals) is 5, or 10, or 50?

References

• Mannion PD, Upchurch P, Hutt S (2011) New rebbachisaurid (Dinosauria: Sauropoda) material from the Wessex Formation (Barremian, Early Cretaceous), Isle of Wight, United Kingdom. Cretaceous Research 32(6): 774–780.
• Osborn, H. F. 1899. A skeleton of Diplodocus. Memoirs of the American Museum of Natural History 1:191–214.
• Windholz, G.J., Porfiri, J.D., Dos Santos, D., Bellardini, F., and Wedel, M.J. 2024. A well-preserved vertebra provides new insights into rebbachisaurid sauropod caudal anatomical and pneumatic features. Acta Palaeontologica Polonica 69(1):39-47. doi: 10.4202/app.01104.2023

doi:10.59350/n02nv-k4z74

To answer Mike’s question from the last post, here’s a nice dorsal of Jimbo. All the material’s from the same quarry and has consistent preservation, and this dorsal is a monster. I didn’t try to measure it through the glass.

Hey guess what? It’s gonna be another really short photo post. Here are some pix of the Jimbo material on display at the Wyoming Dinosaur Center. Many thanks to Tom Moncrieffe of the WDC for taking a good chunk of his day to show me around.

Two partial cervical vertebrae, with part of a little one in between them, and a sectioned rib up on the shelf. I didn’t try to measure these through the glass either, but I’d estimate that each of the cervical centra is a meter and change in length, and both were a few cm longer when complete.

I don’t know if this pneumatic dorsal rib was too big, too dense, or too expensive to CT scan, but Dave Lovelace and colleagues did the next best thing: they sectioned it with a big rock saw. Pretty cool if you ask me.

Next cabinet going around clockwise has these dorsal vertebrae and a couple of broken neural spine tops. The vertebra on the left is the one shown in lateral view at the top of this post.

A tibia and a fibula. This is where it gets a little weird. I measured the other fibula, not on display, as being 116cm long. That sounds big, but it’s only a few cm larger than the fibulae of CM 3018 or AMNH 6341. So either Jimbo was unusually short-legged for the size of its vertebrae, or these limb bones belong to a different individual.

A proximal caudal and a huge chevron in the next cabinet.

And the rest of the caudals in that cabinet, a selection from different spots down the tail, with chevrons.

I have roughly 2376 interesting things I want to blog about, but my head is already about to split open with all the fascinating sauropod anatomy I’ve seen in the past few days, and I’m staring down the barrel of three more days of this. Stay tuned!

doi:10.59350/jp61r-esb50

BYU 11505, a caudal vertebra of a diplodocid from Dry Mesa, in posteroventral view. Note the paired pneumatic foramina on the ventral surface of the centrum.

If you want to find the paleontology and anatomy videos that Mike and I have done (plus one video about open access), they have their own sidebar page now, for your convenience and for our own. It’s, uh, just to the right of where your eyes are pointing right now. You know what, I’m sure you’ve got this.

Make a better living with extensively curated sidebar pages

In fact, we’ve added a few sidebar pages in the comparatively recent past (for a blog in its 17th year). In addition to the video page, we now have some project-specific pages, namely Mike’s Supersaurus, Ultrasaurus and Dystylosaurus in the 21st Century and Mike’s open projects pages, and my own Neural canal projects page. For now the global list of Haplocanthosaurus posts lives on the page for the Wedel et al. (2021) Haplocanthosaurus neural canal paper, but I imagine it’s only a matter of time until I add a page just to track all my business with Haplocanthosaurus. Also, ugh, I still have a few paper that I’ve blogged about, but which don’t have pages, and are therefore just that much harder to find.

And of course we still have all the old standbys: Tutorials, Things To Make and Do, The Shiny Digital Future, and so on.

It might seem kinda dumb to do a post alerting people to stuff that they can find for themselves, but the whole point of having the sidebar pages is that SV-POW! has gotten to be rather unmanageably vast, and anything that helps us — or even you! — get to the right posts quickly is a welcome assist.

The photo up top has nothing to do with any of this, I just thought it would be a fun way to meet our titular mandate.

doi:10.59350/390v5-1q318

Bony spinal cord supports (arrows) in caudal vertebrae of several specimens of Camarasaurus. (a) Right lateral view of neural canal with broken vertebral arch, clearly exposing a bony spinal cord support (MWC 5496). (b) Anterolateral oblique view of the neural canal of the third caudal vertebra (SUSA 515) with a broken vertebral arch displaying a bony spinal cord support. (c) Right lateral view into the neural canal of the fifth caudal vertebra of SUSA 515, also with a broken arch allowing clear visualization of a bony spinal cord support. (d) Posterior view showing bony spinal cord supports in profile (CM 584). All scale bars = 5 cm. Atterholt et al. (2024: fig. 5).

New paper out, er, yesterday:

Atterholt, J., Wedel, M.J., Tykoski, R., Fiorillo, A.R., Holwerda, F., Nalley, T.K., Lepore, T., and Yasmer, J. 2024. Neural canal ridges: a novel osteological correlate of postcranial neuroanatomy in dinosaurs. The Anatomical Record, 1-20. https://doi.org/10.1002/ar.25558

This one started a bit over 10 years ago, on April 9, 2014. That morning I was at the off-site storage facility of the Perot Museum in Dallas, looking at juvenile Alamosaurus material from Big Bend National Park. I found this cute little unfused caudal neural arch, BIBE 45885:

Pro tip: before you go on to the next page or the next specimen, photograph the specimen with your notes and sketch. Trust me on this.

As you can see from my notes, I clocked the little ridges on the inside of the neural canal, but I didn’t know what to make of them. (BTW I’ve used this little feller in a bunch of talks and in my MTE paper last summer with Jessie — see Wedel & Atterholt 2023 and this post.)

That afternoon I was at SMU’s Shuler Museum of Paleontology looking at the holotype of Astrophocaudia, SMU 61732, which was then a new genus, having only been named the year before by Mike D’Emic (2013). And what should I see in this nice caudal:

Now I am not always the fastest on the uptake, but if you smack me in the face twice I start paying attention. Surely it was not a coincidence that the caudal vertebrae of these two not-super-closely-related sauropods had little ridges inside their neural canals. The problem was, I had no idea what they were. For a brief period I got excited by the possibility that they might be some epiphenomenon of big spinal veins, like those of crocs, or big paramedullary diverticula, like those of birds, but they didn’t look quite right for either of those applications (more on this in a future post, maybe, and in the discussion section of the new paper, definitely). I was just flat stumped.

Fast forward to the summer of 2018, by which time I was working with Jessie Atterholt on paramedullary diverticula — laying the groundwork for what would become Atterholt & Wedel (2022) — and generally getting interested in all things neural canal related, including the weird expanded neural canals in the Snowmass Haplocanthosaurus (see Wedel et al. 2021). I wrote to David and Marvalee Wake at Berkeley, both of whom had served on my dissertation committee, and who between them knew more about vertebrate morphology than anyone else I knew, to ask of they’d ever seen similar expansions of the neural canal. To my delight, David wrote right back, “This is a mystery to me. In salamanders there are little strut-like processes from the inside of the neural canal extending inward to support the cord. These are at least partly bony.” That didn’t help with Haplocanthosaurus — at that time still the newer mystery — but it did seem to solve my then 4-year-old quest to figure out what was going on in the Alamosaurus and Astrophocaudia caudals.

We’ll come back to sauropods, I promise. But first we gotta talk about meninges for a bit.

What’s the mater?

One of the bedrock bits of the chordate body plan is a connective tissue notochord running down the body axis, with a big nerve cord sitting on top and a big artery hanging just below. In vertebrates the notochord is mostly replaced by the vertebral column, and we refer to the big nerve cord as the spinal cord and to the big artery as the aorta. The vertebral column doesn’t just give the body stiffness and flexibility and something to hang muscles on, it also has a dorsal bony loop to protect the spinal cord, which we call the neural arch, and in the tail a ventral bony loop to protect the aorta, which we call the hemal arch (the V-shaped hemal arch bones are more commonly referred to as ‘chevrons’). The spinal cord runs through the neural arches of successive vertebrae, which collectively form a protective tube: the neural canal.

(NB: in human anatomy we tend to call the hole for the spinal cord in any one vertebra the ‘vertebral foramen’, and the canal formed by the stacked vertebral foramina the ‘spinal canal’, but in comparative anatomy we tend to use ‘neural canal’ for both the neural arch passage in a single vertebra and the tube formed by all the neural arches.)

The meninges and associated tissues in a mammal.

The spinal cord isn’t just flopping around in the neural canal willy-nilly. Like the brain, the spinal cord is jacketed in a series of protective membranes collectively called the meninges (singular: meninx). Mammals and most (all?) other tetrapods have three meninges:

• outermost is the dura mater, or “tough mother” (same root as ‘durable’)
• just inside the dura is the continuous layer of the arachnoid mater, or “spider(web) mother”
• below the continuous layer of the arachnoid is the subarachnoid space, where cerebrospinal fluid (CSF) circulates; this space is crossed by numerous strands of arachnoid that reach down to the pia, and which look like spiderwebs in dissection, hence the name ‘arachnoid’ (thin blue radiating lines in the diagram above)
• innermost, sitting intimately on top of the spinal cord and spinal nerve roots, is the pia mater, or “tender mother”

In mammals the space between the dura mater and the bony walls of the neural arch is filled with epidural fat. This isn’t unhealthy fat, this is fat used as packing peanuts — the lightest, cheapest thing the body can build.

(We’re a fat-0bsessed culture so it may sound weird to hear fat described as ‘light’ and ‘cheap’, but in fact it is. The metabolic demand of keeping fat cells alive is negligible,* and every other tissue or fluid is heavier and more expensive to maintain. The yellow marrow in the shafts of your long bones is made of fat, and your body will not use that fat for energy even if you are starving to death, because it would just have to be replaced with something heavier and more costly.

*Negligible, but not zero, and the work required to push blood through the extra miles of arteries that serve the fat deposits in obese people can put a lot of extra strain on the heart.)

The human spinal cord in dorsal view, with the denticulate ligaments indicated by asterisks. From Ceylan et al. (2012).

Last but not least there are denticulate ligaments, little sideways extensions of the pia mater that anchor the spinal cord to the inside of the dura mater. I drew them in pink in the diagram, but in dissection they are shiny white or silver; ‘denticulate’ means ‘little tooth’.

Some of these terms have entered the popular lexicon from medicine, particularly ‘meningitis’ and ‘epidural’. Meningitis is an inflammation of the meninges around the brain and spinal cord, which is exactly as horrible and life-threatening as it sounds. An epidural injection is used to deposit anesthetic medication into the epidural fat, where it can soak down through the meninges and bathe the dorsal root ganglia and the dorsal half of the spinal cord, where the sensory neurons (including those that relay pain) are located. In a lumbar puncture, a needle is driven through the dura and the continuous layer of the arachnoid into the subarachnoid space, usually to draw CSF for diagnostic purposes.

The meninges and associated tissues in a non-mammal. NB: this is generalized and simplified, and many structures that may also occupy the neural canal, like spinal veins and paramedullary diverticula, are not shown.

Here’s an important fact I didn’t know in 2014, having been educated most deeply on humans: many non-mammals don’t have epidural fat. Instead, the dura mater can be in contact with or even fused with the periosteum lining the inside of the neural arch, and the denticulate ligaments don’t just go to the dura, they go through it, to contact bone. And any time there’s connective tissue anchoring to bone, there’s a possibility that it will leave an attachment scar.

How do we know this? Salamanders, baby! Bony spinal cord supports were first identified in the northern two-lined salamander, Eurycea bislineata, by Wake and Lawson (1973) — Wake here meaning David Wake, who 41 years later would give me the clue I needed to interpret what I was seeing in sauropod caudal vertebrae. The trail went cold for a while after the 70s, but Skutschas (2009) and Skutschas & Baleeva (2012) found bony spinal supports — a.k.a. neural canal ridges (NCRs) — in a host of salamanders and fish.

The Floodgates Open

When you’re used to sauropods, even “giant” salamanders are pretty dinky. Unedited photo of a vertebra of the Chinese giant salamander, Andrias davidianus, LACM 162475. See the cropped version in Figure 1c of our new paper.

Standing on shoulders of Wake & Lawson and Skutschas & Baleeva, Jessie and I started finding neural canal ridges in all kinds of critters. We visited the herpetology collections at the LACM to verify that we could find them in salamanders, and documented them for the first time in the giant salamanders Andrias japonicus and Andrias davidianus. Skutschas & Baleeva (2012: fig. 5) had figured NCRs in a salmon (Salmo); on a visit to the OMNH I found them in a tuna (Thunnus). Jessie and I visited Dinosaur Journey in Fruita, Colorado, and found examples in Camarasaurus, Diplodocus, and more Apatosaurus vertebrae than you can shake a stick at (as always, many thanks to the MWC Director of Paleontology Julia McHugh for being an awesome host!).

Then other people started finding them. Jessie gave a talk on NCRs at SVPCA in 2019, the lovely meeting on the Isle of Wight, and Femke Holwerda said she’d seen them in a cetiosaur. At the same meeting Mick Green showed us rebbachisaruid material he’d collected from the Isle of Wight, and we found them in a rebbachisaur caudal. Jessie and I went to look for NCRs in the Raymond Alf Museum right here in Claremont, California, and Tara Lepore, who was helping us that day, found them in a hadrosaur caudal.

We even started finding them in previously published papers. Here’s a caudal vertebra of a juvenile Rapetosaurus from Curry-Rogers (2009: fig. 27):

This was a watershed moment — it meant that we could potentially expand our search for NCRs using the published literature. Later Jessie visited the Field Museum and was able to confirm the presence of NCRs in all the real (not cast or reconstructed) vertebrae of the mounted Rapetosaurus.

It gets better! Back in 2009 some goober named Wedel had been an author on the paper describing Brontomerus, and whadda we have here in Figure 6 of that paper?

Brontomerus caudal vertebra OMNH 61248. Taylor et al. (2011: fig. 6).

Truly, we notice what we are primed to notice, and sometimes not a heck of a lot more. In my defense, since getting my antennae out for NCRs I have had my hopes raised and then dashed many times by slightly offset cracks that just happen to run through the midpoint of the neural arch (it makes sense, the bone is thinnest there and most likely to crack), which is presumably what I inferred back when. For a better look at the NCRs in Brontomerus, see Figure 6 in the new paper.

Averianov & Lopatin (2020: fig. 8)

In 2020, Alexander Averianov and Alexey Lopatin described neural canal ridges in the holotype of the Mongolian sauropod Abdarainurus, and they identified them as bony spinal cord supports of the kind described by Skutschas & Baleeva (2012) — correctly, in our view. They’d been unaware of our work, which is not surprising since we’d only presented it in 2019 at SVPCA, and we’d been unaware of theirs. I was, in truth, a little chagrined to have dawdled long enough to be beaten into print (he writes, four and half years later!), but I sent Alexander a congratulatory note and he sent a very gracious response. Anyway, Jessie and I were happy to have more examples, and happy that Averianov & Lopatin’s interpretation of the NCRs agreed with ours.

Ugh — Allosaurus MWC 5492 on the left, hadrosaur RAM 23434 on the right. What a dark day for SV-POW! Scale bars are not sauropod sized so who cares. Atterholt et al. (2024: fig. 8).

And yes, Colin Boisvert, your groady perverted waaaay-too-abundant Allosaurus gets a look in. I hope you’re happy. Traitor.

What now? A short NYABPQ

(Not Yet Asked But Plausible Questions)

How do we know these things in sauropods and other dinos are ossified spinal cord supports and not some other wacky thing? I’d like to write a whole post on this, but in the meantime check out section 4.1 “Alternative hypotheses” on pages 14-16 of the new paper.

But what does it all mean? Section 4.2, “Functional implications”, has some half-baked ideas, but in truth we don’t know yet! We’re hoping someone else will figure that out.

What’s your favorite table in any paper ever? What an oddly specific and specifically flattering question, fictional interlocutor! The answer is Table 3 on page 17 of the new paper, in which we categorize the zoo of neural canal weirdness that we knew of when the paper went to press.

Wait — “that we knew of when the paper went to press”? What the heck does that obvious hedge mean? It means this rabbit hole goes all the way down, and we haven’t yet hit terminal velocity.

You’re kind of a weird dork, huh? Accurate!

I found NCRs in some critter in which they haven’t been documented yet — what should I do? Publish — publish! Jessie and I just spent six years getting this damned thing done and out, and we still have a shedload of weird neural canal stuff we haven’t even touched yet. We are the opposite of territorial, we’d strongly prefer for everyone and their dog to come play in our sandbox (not really ours but you know what I mean) and find lots of cool things and publish a million awesome papers and make neural canals the next hot thing. See Section 4.3, “Directions for future work”.

Stegosaurus NHMUK PV R36730 caudal 34. Right now this one Stego and the hadrosaur pictured above are it for NCRs in Ornithischia — but probably not for long. Maidment et al. (2015: fig. 49).

I haven’t found NCRs but I’d like to — what should I do? Go look in a bunch of neural canals. Seriously. That’s the gig. You might find some in the literature, but I wouldn’t count on a lot. You know who figures dinosaur caudals (1) in AP view (2) with the neural canals fully prepped (3) at sufficient detail to spot NCRs? Very few folks. At a reviewer’s request I spent some time plowing through a bunch of dino literature, and out of all the papers I checked, Susie Maidment’s stegosaur was the only new hit (Maidment et al. 2015, and kudos to Susie for the comprehensive illustrations). But someone who had access to a collection to ‘crawl’, logging all the NCRs, could do bang-up business. I know because that’s what Jessie and I did at Dinosaur Journey in 2018 and 2022, which is why there are so many MWC specimens in the new paper. Outside of Sauropoda we’ve found NCRs in Allosaurus, Ceratosaurus, Stegosaurus, and an indeterminate hadrosaur, and I don’t need to tell you that that is hardly a comprehensive survey of Dinosauria. We didn’t do more because we’re mortal and we wanted to get our sauropod paper out before it metastasized further, not because we were done, or even started, really. So if you want to discover new anatomy in dinosaurs, here’s a path with a very high likelihood of success.

What are you going to do next? The Greater Atterholt-Wedel Neural Canal Exploration Project (GAWNCEP) is still rolling, mostly under Jessie’s direction at the moment. As promised above, more weirdness is coming, watch this space. And when I’m not GAWNCEPtualizing, I, ahem, owe some folks some work on some projects. Just a few!

Special Thanks

Because you’re not supposed to thank your own coauthors in the acknowledgements: many thanks to Ron Tykoski and Tony Fiorillo for never giving up during the entire decade that it took to get from our first coauthored conference presentation to our first coauthored paper. Thanks to Femke and Tara for finding more NCRs and joining us on the paper, to John Yasmer for CT wizardry, and to Thierra Nalley for 3D recon wizardry and for being our resident non-sauropod vertebra expert. Y’all are great folks and it’s a pleasure to share the byline with you.

Dingler (1965: fig. 12) showing the elaborate ladder-like denticulate ligament system that suspends the spinal cord inside the synsacrum of a goose. Caption and labels translated by London Wedel.

At a crucial point in this project I needed a translation of Dingler (1965), which is was only available in German. I hired my son, London Wedel, then a high school senior taking German 4, to translate it. That translation will go up on the Polyglot Paleontologist at some point, but in the meantime you can get it here (Dingler 1965 bird spinal cord paper (translation)) and at the hyperlink in the references below. London just started classes at European University Viadrina Frankfurt (Oder), pursuing his long-held dream of attending university in Germany, and I couldn’t be prouder.

David Wake was the lecturer for the evolution course in my first semester at Berkeley. I invited him to serve on my qualifying exam committee because I knew he would terrify me into working my butt off — not, I must clarify, because he was a terrifying person, but because the depth and breadth of his erudition intimidated the crap out of me. I invited him to serve on my dissertation committee for the same reason. He always pushed me to think more broadly — in time, space, development, function, phylogeny, and evolution. Those seeds didn’t all germinate right away, but I can see that a lot of my intellectual range now is a result of his example and his prodding back then. I never had the opportunity to collaborate with David directly, but I get immense satisfaction from the fact that this entire project was born out of a suggestion of his. My coauthors Jessie Atterholt and Tara Lepore are also proud Berkeley grads, and we’re all happy to dedicate the new paper to the memory of David Wake.

References

• Atterholt, J., & Wedel, M. J. (2022). A computed tomography-based survey of paramedullary diverticula in extant Aves. The Anatomical Record, 306(1), 29–50. https://doi.org/10.1002/ar.24923
• Atterholt, J., Wedel, M.J., Tykoski, R., Fiorillo, A.R., Holwerda, F., Nalley, T.K., Lepore, T., and Yasmer, J. 2024. Neural canal ridges: a novel osteological correlate of postcranial neuroanatomy in dinosaurs. The Anatomical Record, 1-20. https://doi.org/10.1002/ar.25558
• Averianov, A. O., & Lopatin, A. V. (2020). An unusual new sauropod dinosaur from the Late Cretaceous of Mongolia. Journal of Systematic Palaeontology, 18(12), 1009–1032.
• Ceylan, D., Tatarlı, N., Abdullaev, T., Şeker, A., Yıldız, S. D., Kele¸s, E., Konya, D., Bayri, Y., Kılıç, T., & Çavdar, S. (2012). The denticulate ligament: Anatomical properties, functional and clinical significance. Acta Neurochirurgica, 154, 1229–1234.
• Curry Rogers, K. (2009). The postcranial osteology of Rapetosaurus krausei (Sauropoda: Titanosauria) from the Late Cretaceous of Madagascar. Journal of Vertebrate Paleontology, 29, 1046–1086.
• D’Emic, M. D. (2013). Revision of the sauropod dinosaurs of the Lower Cretaceous Trinity Group, southern USA, with
  the description of a new genus. Journal of Systematic Palaeontology, 11(6), 707–726.
• Dingler, E. C. (1965). Einbau des Rückenmarks im Wirbelkanal bei Vögeln [Positioning of the spinal cord in the vertebral canal in birds; in German]. Verhandlungen der Anatomischen Gesellschaft, 115, 71–84. (Dingler 1965 bird spinal cord paper (translation))
• Maidment, S. C. R., Brassey, C., & Barrett, P. M. (2015). The postcranial skeleton of an exceptionally complete individual of the plated dinosaur Stegosaurus (Dinosauria: Thyreophora) from the Upper Jurassic Morrison Formation of Wyoming, USA. PLoS One, 10(10), e0138352.
• Skutschas, P. P. (2009). Re-evaluation of Mynbulakia Nesov, 1981 (Lissamphibia: Caudata) and description of a new salamander genus from the Late Cretaceous of Uzbekistan. Journal of Vertebrate Paleontology, 29(3), 659–664.
• Skutschas, P. P., & Baleeva, N. V. (2012). The spinal cord supports of vertebrae in the crown-group salamanders (Caudata, Urodela). Journal of Morphology, 273(9), 1031–1041.
• Taylor, M. P., Wedel, M. J., & Cifelli, R. L. (2011). A new sauropod dinosaur from the Lower Cretaceous Cedar Mountain Formation, Utah, USA. Acta Palaeontologica Polonica, 56(1), 75–98. https://doi.org/10.4202/app.2010.0073
• Wake, D. B., & Lawson, R. (1973). Developmental and adult morphology of the vertebral column in the plethodontid salamander Eurycea bislineata, with comments on vertebral evolution in the Amphibia. Journal of Morphology, 139(3), 251–299.
• Wedel, M. J., & Atterholt, J. (2023). Expanded neurocentral joints in the vertebrae of sauropod dinosaurs. In R. K. Hunt-Foster, J. I. Kirkland, & M. A. Loewen (Eds.), 14th Symposium on Mesozoic Terrestrial Ecosystems and Biota. The Anatomical Record, 306(S1), 256–257.
• Wedel, M. J., Atterholt, J., Dooley, A. C., Jr., Farooq, S., Macalino, J., Nalley, T. K., Wisser, G., & Yasmer, J. (2021). Expanded neural canals in the caudal vertebrae of a specimen of Haplocanthosaurus. Academia Letters, 911. https://doi.org/10.20935/AL911

Trunk vertebra of a tuna (Thunnus), OMNH RE 0042, showing paired bony spinal cord supports

Here’s a grab-bag of follow-up stuff related to our new paper on neural canal ridges in dinos (Atterholt et al. 2024, see the previous post and sidebar page).

Neural canal ridges, or bony spinal cord supports?

I got into the habit of calling the inwardly-projecting bony prominences in the neural canals of sauropods and other critters “neural canal ridges” partly because I was thinking about them for literally years before I knew what they were, and I had to call them something, and partly because “neural canal ridges” is a reasonably accurate descriptive term that does not imply a specific function. NCRs became part of my internal lexicon.

Later on, thanks first to David Wake, and later to Skutschas & Baleeva (2012), we discovered that extant fishes and salamanders have bony spinal cord supports, and we think that’s the best explanation for why NCRs show up in so many dinos. “Bony spinal cord supports” is not function-neutral, it takes a stand. Since the whole point of our paper is not only to describe these things in dry terms, but to also take a stand on their associated soft tissues, it would be more coherent to cowboy up and call them “bony spinal cord supports” instead of “neural canal ridges”, and that’s exactly what Jessie Atterholt did in the tables and figure captions of the new paper. Also, sometimes the bony spinal cord supports are not ridges, but shelves or planks or spikes — check out that tuna vertebra up top, and the salamander verts in Fig. 1 of the new paper — so “neural canal ridges” doesn’t even accurately describe them all the time. If I call them NCRs in my blogging, it’s out of habit, and because — so far — that does accurately describe the appearance of the bony spinal cord supports in dinos.

Denticulate ligaments: sometimes double, sometimes absent

Here’s something that turned up late in our research on this project. Elvan et al. (2020) is a nice paper on the denticulate ligaments in developing humans (it is of course tragic when fetuses are miscarried or stillborn, but what we learn from them can help keep others alive). One of the curious things they mention, and figure, is that the denticulate ligaments that suspend the spinal cord inside the dura mater are occasionally doubled on one side, and occasionally absent.

Elvan et al. (2020: fig. 1)

This shouldn’t be super surprising. Variation exists in part because developmental programs are messy. “Asymptomatic anatomical variation”, “pathological variation”, “congenital anomaly” (“birth defect”), and “fatal malformation” are points on a spectrum — and all of us are somewhere on that spectrum. “Normal” human anatomy is normal in the statistical sense, in that the majority of folks end up in the big middle, but that middle encompasses a lot of variation, and there are long tails in lots of directions for almost every body part and body system, and things can sometimes be pretty non-standard under the hood without causing noticeable symptoms.

Here’s a whole paper on a six-legged rat (Brown 1996). Click to embiggen.

In particular, if there’s a developmental program for building structure X — whether structure X is a hair follicle, a muscle, nerve, or blood vessel, a finger or toe, a gill arch, a vertebra and its associated body segment, or an entire limb — then inevitably there will be counting errors from time to time, omissions or duplications, and embryos, fetuses, or offspring produced with fewer or more of structure X than is typical. At the small end of the scale we might not even notice, and at the large end of the scale the variation might not be viable.

In between those extremes you sometimes get a memorable villain.

ANYWAY, finding the Elvan et al. paper was an “Aha!” moment for me. Back in 2018 when I’d been photographing tuna vertebrae in the OMNH collections, I found some that had not one but two inward-pointing bony spikes on each side. I figured these were just a fancier system of bony spinal cord supports, probably indicating doubled denticulate ligaments. I didn’t know for sure that the latter existed, so in assembling figures for the paper we went with the tuna vertebra that most closely resembled the salmon vertebra figured by Skutschas & Baleeva (2012). Later on, the Elvan et al. paper confirmed for us that doubled denticulate ligaments sometimes occur, at least in humans, so it’s plausible that they happen in fish, too, and maybe regularly given that I found the quad-spike setup in multiple tuna vertebrae. But that seemed like a lot of extra yap and figures to make a rather minor point, which is why you’re hearing about this in a blog post instead of in the paper.

Another vertebra of OMNH RE 0042, showing (what I infer to be) paired bony spinal cord supports

I assume that these spikes and whatever attaches to them were described back in the 1800s in some obscure paper, probably published in Germany or Great Britain, but if so I’ve not yet tracked down that hypothetical publication. Even if said publication exists, I’m sure it’s illustrated with a hand-drawn diagram. It occurs to me that someone could go to a fish market, buy a chunk of tuna with the bone in, do a little careful dissecting, get some hi-res color photos, and have everything they’d need to publish a nice little paper, either describing these spikes and their soft-tissue correlates for the first time, or redescribing them and providing the first good color photos. Realistically I’m unlikely to get around to that, so if you want it, go nuts.

Science…and dinner

Citing the Deep Magic

I’m gonna geek out for a sec on the developmental underpinnings of the denticulate ligaments and the vertebrae they’re associated with. And to do that, we have to orient ourselves to the various bits sticking out of the spinal cord and how they relate to the vertebral column.

Here’s a chunk of sauropod tail in left lateral view (modified from Wedel et al. 2021: fig. 2a) — specifically, a 3D-printed section of Haplocanthosaurus tail that Alton Dooley put together for the “Tiny Titan” exhibit at the Western Science Center a few years ago, seen in medial view in the second image down in this post. The laterally-facing bony loop formed by the central and zygapophyseal articulations of two adjacent vertebrae is the intervertebral foramen, and it’s through the intervertebral foramina that the spinal nerves leave the neural canal (blood vessels enter and leave through these openings, too). Assuming that sauropods were built like reptiles rather than mammals, and lacked epidural fat, a horizontal section through this bit of tail on the black line indicated by the Xs might look something like this:

Anterior is toward the top now. There’s a lot going on in this image, so let’s take it one piece at a time. The neural arch pedicles are the paired black-and-white pillars on either side of the spinal cord, defining the lateral walls of the neural canal. (The section in the photo also went through the caudal ribs but I was too lazy to draw those.) The meninges — the dura, arachnoid, and pia mater, and the subarachnoid space — are by now old friends; this diagram is showing us the same structures as this one from the previous post, just in horizontal section rather than transverse. Bundles of spinal nerve roots come together to form the spinal nerves, which exit the neural canal at the intervertebral foramina between adjacent neural arch pedicles. The various meninges form little sideways-projecting meningeal sleeves over the first little section of each spinal nerve; imagine making 3-layer coveralls for a centipede and you’ll have a good mental model of the whole meningeal system of the spinal cord (for real geekery, past the ends of the meningeal sleeves the nerves are jacketed in a different connective tissue called epineureum). The denticulate ligaments attach the spinal cord to the dura mater (or even through the dura mater) level with the neural arch pedicles of the vertebrae, so if you’re looking at a section of the cord in dorsal or ventral view you’ll see bundles of spinal nerve roots (at the intervertebral foramina) alternating cranio-caudally with denticulate ligaments (in between intervertebral foramina). You can check that with the dorsal-view photos of human spinal cords above and in this image in the previous post.

(Note for any confused med students who might be reading this: anatomical position for humans is upright, so horizontal and transverse sections are synonymous. Most other animals carry their bodies horizontally, so a horizontal section through a sauropod would be similar to a coronal or frontal section through a human vertebral column. Also, humans do have epidural fat, unlike this sauropod, and our denticulate ligaments do not go through the dura mater to attach to bone. So don’t use these sauropod diagrams to study for your human anatomy courses! Instead, a great learning exercise would be to redraw this diagram so it was accurate for a human. If you do that, feel free to drop me a line in the comments and we can talk about your results. Standing offer, good forever.)

At the bottom of the image I labeled segmental muscles and intermuscular septum. You’ve seen these before, although you may not have known it: they make the zig-zag patterns in the meat of fishes, where we call the segmental muscles myomeres (“muscle parts”) and each intermuscular septum a myoseptum, plural myosepta (“muscle partition”).

Lateral view of the trunk muscles of a salmon, Salmo. Liem et al. (2001: fig. 10-16)

Each myomere is associated with a particular spinal level — a paired set of spinal nerves, like the C7 or T10 spinal nerves in a human — and each myoseptum is associated with a particular vertebra, like, er, C7 or T10 in a human (or a sauropod, although we’d call it D10 for dorsal 10 in a sauropod; sauropod dorsals all have big ribs that were mobile at some point, so there’s no need to separate them into thoracic [dorsals with mobile ribs] and lumbar [dorsals without mobile ribs]). Put a pin in that thought for a moment, we need to wrap up something fishy.

Myomere cones in a salmonid, Salmo (A), and a dogfish, Squalus (B, C). Liem et al. (2001: fig. 11-4).

You maybe looking at the mild zig-zaggy-ness of the myomeres in that first salmon diagram, and the target-like concentric circles in the photo of the salmon steaks up above, and thinking something doesn’t add up. And you’re right — the surface zig-zaggy-ness of the myomeres is not their full extent, they have anterior and posterior cones arranged concentrically, presumably to allow each myomere to exert force over more of the vertebral column. And that’s why fish comes apart in such interesting ways when you eat it, especially if it’s cooked.

Anyway, back to the segmental muscles and intermuscular septa in the sauropod — and in yourself, for that matter. It’s not immediately obvious that amniotes are built on the same myomere/myoseptum infrastructure as sharks and salmon, because our development involves a lot of splitting and recombining and stretching of muscles across multiple spinal levels. But if you go deep enough, we all have some single-segment muscles that bridge adjacent body segments — intercostal muscles between our ribs, and interspinales, intertransversarii, and rotatores breves between adjacent vertebrae.

The relevant slide from my lecture on deep back muscles. Rotatores aren’t shown because I’d covered them on a different slide, with the rest of the transversospinal group. I should do a whole post on them sometime.

Now here’s the part that I think is awesome, what this whole section has been building toward: the myomeres and myosepta were there from very early on in development, and the myosepta originally ran from spinal cord to skin. Denticulate ligaments are just what we call the little stretch of myoseptum between the spinal cord and the dura mater, sorta like how we use ‘Foothill Boulevard’ for the stretch of US Route 66 that runs through Claremont and adjacent townships. The pedicles of the neural arches — in fact, the entire left and right halves of each neural arch — form within the myosepta. The light gray boxes around “denticulate ligament”, “neural arch pedicle”, and “intermuscular septum” in my cross-sectional diagram above unite the different portions or aspects of the embryonic myoseptum. I didn’t work all this out myself, mind, I learned it from Skutschas & Baleeva (2012), who demonstrate it all very convincingly with developmental work on larval salamanders.

And that brings us to the weirdness of mammals.

NCRs? No thanks, we’re mammals

I’ve gotten some questions about whether mammals could have NCRs. I doubt it. Not to put too fine a point on it, but as a species we just care more about our own anatomy and that of dogs and cattle and rabbits and rats, than we do about any other critters, and I think if mammals had NCRs they’d have been found and logged by now.

Also, I don’t think we mammals have the capacity to have bony spinal cord supports, because those are the attachment scars of the denticulate ligaments to the inner walls of the neural canals, and our denticulate ligaments don’t work that way. Our denticulate ligaments connect our spinal cords to our dural sacs, but we have epidural fat between the dura and the neural arch pedicles, and apparently when in development the dura pulls away from the neural arch pedicles and epidural fat starts to be laid down in between, whatever embryonic connection existed between the denticulate ligament and the rest of the myoseptum is broken.

I said “I doubt it” rather than a flat “no” because apparently there is very little to no epidural space in the cervical region of most mammals. IF there are mammals in which the dura mater fuses to the periosteum in the cervical region, then maybe the embryonic myoseptal connection could be maintained, the resulting denticulate ligaments could be tied down to bone, and bony spinal cord supports could exist. I wouldn’t rule it out, because if there’s one thing we as a species are even worse about than caring about non-mammals, it’s peering into neural canals.

But we’re working on it.

References

• Atterholt, J., Wedel, M.J., Tykoski, R., Fiorillo, A.R., Holwerda, F., Nalley, T.K., Lepore, T., and Yasmer, J. 2024. Neural canal ridges: a novel osteological correlate of postcranial neuroanatomy in dinosaurs. The Anatomical Record, 1-20. https://doi.org/10.1002/ar.25558
• Brown, M.D., 1996, February. A Six-Legged Rattus (Todentia: Muridae) in Oklahoma. Proceedings of the Oklahoma Academy of Science 76: 91-92.
• Elvan, Ö., Kayan, G. and Aktekin, M., 2020. The anatomical features of denticulate ligament in human fetuses. Surgical and Radiologic Anatomy 42: 969-973.
• Liem, K.F., Bemis, W.E., Walker, W.F., and Grande, L. 2001. Functional Anatomy of the Vertebrates. (3rd ed.). Thomson/Brooks Cole, Belmont, CA.
• Skutschas, P. P., & Baleeva, N. V. (2012). The spinal cord supports of vertebrae in the crown-group salamanders (Caudata, Urodela). Journal of Morphology, 273(9), 1031–1041.

Luke Horton asked in a comment on a recent post:

Given the chance to examine a titanosaur cadaver with your hypothetical army of anatomists, what would you look for first?

*FACEPALM* How we’ve gone almost 17 years without posting about a hypothetical sauropod dissection is quite beyond my capacity. I am also contractually obligated to remind you that the TV show “Inside Nature’s Giants” shows dissections of a whale, elephant, giraffe, tiger, anaconda, giant squid, etc., so it’s probably the closest we’ll ever get. Go look up photos of Dr. Joy Reidenberg standing, um, amidst a partially-dissected whale, or just watch that episode, and your sauropod-dissection-visualizer will be properly calibrated.

To get back to Luke’s question, there are loads of interesting things that could be dissected in a sauropod, but since the remit here is Matt Wedel x titanosaur, there’s only one possible answer: the lung/air sac system and its diverticula. For several reasons:

Hypothetical reconstruction of the lungs (red) and air sacs (blue, green, and gray) in Haplocanthosaurus CM 879. I’d love to know how close this is to reality. Wedel (2009: fig. 10).

First and most obviously, I’ve spent the last quarter-century trying to infer as much as possible about the respiratory systems of sauropods based on the patterns of pneumaticity in their skeletons, and I’d kill for the opportunity to check the accuracy of my inferences — and those of all my fellow-travelers in the sauropod and dinosaur respiration biz, like Daniela Schwarz and Emma Schachner and Tito Aureliano and many others.

Sauropod respiratory system modeled on that of a bird. I’ll bet the correspondence wasn’t this close. (Also, since making this figure 20 years ago, I’ve learned that the abdominal air sacs of ostriches are actually rather small, although the perirenal, femoral, and subcutaneous diverticula of the abdominal air sacs are extensive; see Bezuidenhout et al. 1999). Wedel and Cifelli (2005: fig. 14).

Second, I am intrigued/haunted by the possibility that extant birds might not represent the apex of saurischian lung/air sac evolution. Birds survived the K-Pg disaster because they were small; respiratory efficiency had little or nothing to do with it (evidence: all the other small-bodied tetrapods that survived, like the many, many squamate and mammalian lineages). To me it would be a wild coincidence if the tiny dinosaurs that survived also just happened to be The Bestest (TM) at some anatomical/physiological thing unrelated to their survival. In fact, given how sensitive birds are to airborne dust and ash, I wonder if their fancy lungs weren’t more of a hindrance than a help in the dusty, sooty, iridium-laced post-impact world. Anyway, there are interesting clues that the air sac systems of extant birds are just one subset of a much greater original diversity, like most (all?) birds starting out embryologically with a dozen or so air sacs, which get simplified to the usual 9 or fewer by fusions. What did other dinosaurs do with their 12 (or more?) air sacs? If any dinosaurian clade was going to push the capabilities of the “avian” lung/air sac system in interesting directions and to fascinating extremes, sauropods seem like a good bet.

Rib articulation angles in the dorsal vertebrae of (a) Lufengosaurus, (b) Diplodocus, (c) Haplocanthosaurus, (d) Tyrannosaurus, and (e) an ostrich. Anterior is to the right. Diplodocus and Haplocanthosaurus are pretty wildly different considering they coexisted in the Morrison. I really gotta write a whole post about that. Boisvert et al. (2024: fig. 12).

So I’m intrigued by the idea that extant birds show us one way that a saurischian lung/air sac system can work, but don’t exhaust the territory, anymore than kangaroos show us all the ways that mammals can reproduce. Maybe sauropods had even better lungs than birds! Or maybe not. Likely they were doing their own weirdly specialized thing — or many weirdly specialized things — that left few to no diagnostic traces in their skeletons. We can be pretty confident that at least some of the pneumatic diverticula of sauropods worked essentially identically to how they do in birds (see Woodruff et al. 2022 and this post), and mid-dorsal pneumatic hiatuses in juvenile sauropods — predicted by me in 2003, found by Melstrom et al. (2016) and Hanik et al. (2017) — suggest that their air sac systems were broadly comparable. On the other hand, the variety of rib articulation angles just within Morrison sauropods tells us they weren’t all ventilating their air sacs in quite the same way (Boisvert et al. 2024), despite broad similarities with other dinos at the levels of rib osteology (Wang et al. 2023) and whole-thorax construction (Schachner et al. 2009, 2011). (Aside: why the hell didn’t I work a citation of Wang et al. 2023 into the Dry Mesa Haplo paper? I can only conclude that I am at least occasionally an idiot.) Whatever was going on, I’m pretty sure sauropods didn’t look exactly like 60-ton turkeys on the inside, but we don’t have a ton of real data on how they differed. It would be amazing to find out.

The mounted Rapetosaurus skeleton at the Field Museum, traced from a photo. Specific weird things to note: neck about twice as long as tail, cervical vertebrae about twice as tall as dorsals, and smallish pelvic bones relative to hindlimbs (= skinny posterior abdomen, at least dorsoventrally). See this post for details.

Third, if any sauropods were going to rival or exceed birds in fancy under-the-hood anatomical and physiological adaptations, my money would be on titanosaurs. They were morphologically disparate, phylogenetically diverse, geographically widespread, they independently evolved to giant size more times than any other sauropod clade, and their growth rates were wild. I’d dissect any sauropod I got access to (uh duh), but a titanosaur would be particularly appealing. Which titanosaur? Probably Rapetosaurus: we know it grew very fast early on (Curry Rogers et al. 2016, and see implications for the nervous system in Smith et al. 2022), it had a highly pneumatic vertebral column (O’Connor 2006), its body proportions were pretty wacky, and it had other features of interest to me, like expanded neurocentral joints (see Wedel and Atterholt 2023 and this post) and neural canal ridges (see Atterholt et al. 2024 and this post).

I used this photo of a Rapetosaurus caudal vertebra a few posts ago to illustrate the neural canal ridges, but — like many other sauropods — it also has very expanded neurocentral joints forming boutons. From Curry Rogers (2009: fig. 27).

Oh, and if I got to dissect more than one sauropod, the rest of my top 5 choices in order would be:

• the owner of BYU 9024 (Supersaurus? Giant ancient individual of Barosaurus? Are those even different things? Dissecting this critter could tell us!), Barosaurus being the most diplodocid-y and least titanosaur-y neosauropod I know of, and BYU 9024 being from a hellaciously big individual no matter what its classification;
• the Snowmass Haplocanthosaurus, because I have just so many questions about all the weird stuff going on with its tail (see Wedel et al. 2021 and this post for starters); 
• Omeisaurus or Xinjiangtitan, to represent a maximally derived-but-also-weird non-neosauropod;
• Sauroposeidon, for obvious emotional reasons (but not enough to dethrone the others).

After that? Probably Isanosaurus or Melanorosaurus or something else waaaay down the tree, so I could see how much of the sauropod kit was in place from the get-go (probably most of it).

Bone vs joint space in the proximal caudals of the Snowmass Haplocanthosaurus. I’d give one non-essential organ to dissect that tail!

And after the respiratory system, next up for me would be the spinal cord and any related morphological specializations of the neural canal — see Table 3 in Atterholt et al. (2024) for a running tally, and this page. Then intervertebral joints, digestive tract, and reproductive system (neither of the last two leave anything useful in the way of skeletal traces), in that order. Arguably the intervertebral joints would be a bigger score for sauropod paleobiology than spinal cord stuff, but maybe not, and having squelched my emotional pick among sauropod taxa, I’m letting my emotions rule when choosing body systems to dissect. I also am intensely interested in the possibility of protofeathers in sauropods, but you don’t have to dissect those, you can just see if any are present, so I’d cheat a little and note any integumentary specializations en passant. (Remember than an animal can have hairs without being hairy [naked mole rats, rhinos, manatees, dolphins], ditto for feathers.)

So that’s the sauropod and the body system I’d dissect first, if given the chance. What’s your answer?

References

• Atterholt, J., Wedel, M.J., Tykoski, R., Fiorillo, A.R., Holwerda, F., Nalley, T.K., Lepore, T., and Yasmer, J. 2024. Neural canal ridges: a novel osteological correlate of postcranial neuroanatomy in dinosaurs. The Anatomical Record, 1-20. https://doi.org/10.1002/ar.25558
• Bezuidenhout, A.J., H.B. Groenewald, and J.T. Soley. 1999. An anatomical study of the respiratory air sacs in ostriches. Onderstepoort Journal of Veterinary Research 66:317-325.
• Boisvert, Colin, Curtice, Brian, Wedel, Mathew, & Wilhite, Ray. 2024. Description of a new specimen of Haplocanthosaurus from the Dry Mesa Dinosaur Quarry. The Anatomical Record, 1–19. http://doi.org/10.1002/ar.25520
• Curry Rogers, Kristina. 2009. The postcranial osteology of Rapetosaurus krausei (Sauropoda: Titanosauria) from the Late Cretaceous of Madagascar. Journal of Vertebrate Paleontology 29:1046-1086.
• Curry Rogers, K., M. Whitney, M. D. D’Emic, and B. Bagley. 2016. Precocity in a tiny titanosaur from the Late Cretaceous of Madagascar. Science 352:450–454.
• Hanik, Gina M., Matthew C. Lamanna and John A. Whitlock. 2017. A juvenile specimen of Barosaurus Marsh, 1890 (Sauropoda: Diplodocidae) from the Upper Jurassic Morrison Formation of Dinosaur National Monument, Utah, USA. Annals of Carnegie Museum 84(3):253–263.
• Melstrom, Keegan M., Michael D. D’Emic, Daniel Chure and Jeffrey A. Wilson. 2016. A juvenile sauropod dinosaur from the Late Jurassic of Utah, USA, presents further evidence of an avian style air-sac system. Journal of Vertebrate Paleontology 36(4):e1111898. doi:10.1080/02724634.2016.1111898
• O’Connor, P.M. 2006. Postcranial pneumaticity: an evaluation of soft-tissue influences on the postcranial skeleton and the reconstruction of pulmonary anatomy in archosaurs. Journal of Morphology 267: 1199-1226.
• Schachner, E.R., Lyson, T.R. and Dodson, P., 2009. Evolution of the respiratory system in nonavian theropods: evidence from rib and vertebral morphology. The Anatomical Record 292(9): 1501-1513.
• Schachner, E.R., Farmer, C.G., McDonald, A.T. and Dodson, P., 2011. Evolution of the dinosauriform respiratory apparatus: new evidence from the postcranial axial skeleton. The Anatomical Record 294(9): 1532-1547.
• Smith, Douglas H., Rodgers, Jeffrey M., Dollé, Jean-Pierre, and Wedel, Mathew J. 2022. Giraffes vs. blue whales vs. dinosaurs: contest reveals which one builds its nervous system fastest to evade predators. Scientific American, https://www.scientificamerican.com/article/giraffes-vs-blue-whales-vs-dinosaurs-contest-reveals-which-one-builds-its-nervous-system-fastest-to-evade-predators/
• Wang, Y.Y., Claessens, L.P. and Sullivan, C., 2023. Deep reptilian evolutionary roots of a major avian respiratory adaptation. Communications Biology, 6(1), p.3.
• Wedel, M.J. 2003a. Vertebral pneumaticity, air sacs, and the physiology of sauropod dinosaurs. Paleobiology 29:243-255.
• Wedel, M.J. 2009. Evidence for bird-like air sacs in saurischian dinosaurs. Journal of Experimental Zoology 311A:611-628.
• Wedel, M.J., and Atterholt, J. 2023. Expanded neurocentral joints in the vertebrae of sauropod dinosaurs. In Hunt-Foster, R.K., Kirkland, J.I., and Loewen, M.A. (eds), 14th Symposium on Mesozoic Terrestrial Ecosystems and Biota. The Anatomical Record 306(S1):256-257.
• Wedel, M.J., and Cifelli, R.L. 2005. Sauroposeidon: Oklahoma’s native giant. Oklahoma Geology Notes 65 (2):40-57.
• Wedel, Mathew; Atterholt, Jessie; Dooley, Jr., Alton C.; Farooq, Saad; Macalino, Jeff; Nalley, Thierra K.; Wisser, Gary; and Yasmer, John. 2021. Expanded neural canals in the caudal vertebrae of a specimen of Haplocanthosaurus. Academia Letters, Article 911, 10pp.
• Woodruff, D. Cary, Wolff, Ewan D.S., Wedel, Mathew J., Dennison, Sophie, and Witmer, Lawrence M. 2022. The first occurrence of an avian-style respiratory infection in a non-avian dinosaur. Scientific Reports 12, 1954. https://doi.org/10.1038/s41598-022-05761-3

doi:10.59350/ajsh7-42642

A middle caudal vertebra of a diplodocid, presumably Tornieria africana, on display at the Museum fur Naturkunde Berlin, in left lateral view.

Quick backstory: this post at Adam Mastroianni’s Experimental History led me to this post at Nothing Human, and poking around there led me to another good’un: “Shallow feedback hollows you out”. That post really hit for me, and it made me think about SV-POW! Especially this bit:

Suppose you don’t want to lose your ability to think new thoughts and see new things. What are your options?

The best remedy is to write to the single smartest person you know who cares a lot about your topic of interest.

I have two thoughts about this. The first, which dovetails nicely with the thesis of that post, is that SV-POW! staying relatively small is probably a good thing. We’ve never written with the goal of growing our readership, and I think that’s kept us from being tempted by a lot of bad habits whose deleterious effects you can see play out over and over again across the whole internet. Our habit of posting on a completely irregular schedule on whatever topics we like has been doubly beneficial: it’s kept us sane (for reasons explored in this post), and it’s probably kept our readership low,* which has kept the temptation to write for marginal readers from ever getting off the ground. In case that sounds insulting or dismissive to our readers, let me clarify: we love our readers, and we’d rather have our little community of dedicated weirdos than any other set.

(Don’t get me wrong, I like it when one of our posts goes viral, but I like it in the same sense that I like watching a comet: it’s a cool phenomenon that I feel is beyond my influence. I enjoy it, but it doesn’t affect how I conduct myself.)

*Having written that, I wonder now if our irregular posting schedule has possibly deepened the dedication of those readers who can tolerate it — it could be a form of intermittent reinforcement, which has been implicated in gambling addiction.

That leads to my second thought: at any given time in the 17-year history of this blog, we’ve had a small but dedicated cadre of commenters, but the makeup of that group has changed over time. This has also had a salutary effect: for every post I’ve ever written here, I could be pretty sure that at least some of the regulars would see it and comment, but the one thing of which I could be absolutely certain is that the post would be seen and read by Mike. For most posts, Mike probably cares as much or more about what I’m writing than anyone else in the world, he will absolutely call me to account if he catches any weaknesses of evidence or reasoning, and he’ll do it publicly, in our own comment section. These are all good things! As my Constant Reader, Mike’s helped enforce the good habits of mind and of writing that are the subject of that Nothing Human “Shallow feedback” post.

The same Tornieria vertebra in dorsolateral oblique view, showing some pneumatic features on the lateral aspect of the neural spine. The pocks on the centrum are also raising my pneumaticity antennae, but I can’t be sure from my limited set of 16-year-old photos. When Diplodocus caudals have pneumatic features this far back in the tail, they’re more commonly on the centrum than the arch, but diverticula gonna diverticulate.

Speaking of, I also really liked this bit from the first comment on that post, by Mo Nastri:

…the details change but the general pattern is the same. In each case the [once great] intellectual in question is years removed from not just the insights that delivered fame, but *the activities that delivered insight*.

To the extent that this blog has escaped enshittification, it’s probably because Mike and I are not removed from the activities that deliver insight. We care more about sauropod vertebrae (and pig skulls, etc.) than we do about clicks. And at this point, I’m confident that we always will. If we were ever in danger of click-maximizing behavior, it was probably back in the early days, and even then the risk was minimal. We love our weird little niche blog just as it is, weird and niche-y and little.

The possibly-surprising conclusion I’m building toward is that we’ve probably made SV-POW! a better experience for our readers (minimally, in that it still exists to be read) by not caring about our readership, and by not writing to please or impress anyone other than ourselves and each other. And that in turn has kept SV-POW! viable for us as well.

So if you’re here, great! We’re happy to have you — as an interested person, rather than a click. If you like what we’re doing, stay tuned. We’re gonna do a lot more of the same.

When our paper on neural canal ridges came out last year (Atterholt et al. 2024), I hoped that it would inspire other people to go peer inside neural canals and discover a lot more of them. My wish was granted, and quickly. In early October I was contacted by William Jude Hart, then an undergrad at Hofstra University in New York (he graduated in December). He was making a poster for the upcoming SVP meeting on a specimen of the large tomistomine crocodilian Thecachampsa, specifically an anterior caudal vertebra with pretty darned unambiguous neural canal ridges:

Since then we’ve found more examples, in both extinct and extant crocodilians, and William invited me to be his coauthor on the description. Our first salvo, Hart and Wedel (2025), is a slide presentation at the 5th Palaeontological Virtual Congress, which is going on right now. Find us in the thematic session, “Unraveling crocodylomorph evolution: insights from fossils and new methodologies“. All of the 5PVC presentations will be up for another week, and registration is measly 5 Euros, so if you’re curious about our findings — and a great many other fascinating paleo things — go check it out.

More 5PVC news shortly. And if you’re interested in neural canal ridges, or neural canal anything, or pretty much any kind of anatomy whatsoever, I have good news: there are tons of things waiting to be discovered by curious folks. I mean, heck, the first neural canal ridges in crocs — not an obscure or understudied clade — were found by an observant undergrad.

Come play.

References

• Atterholt, J., Wedel, M.J., Tykoski, R., Fiorillo, A.R., Holwerda, F., Nalley, T.K., Lepore, T., and Yasmer, J. 2024. Neural canal ridges: a novel osteological correlate of postcranial neuroanatomy in dinosaurs. The Anatomical Record, 1-20. https://doi.org/10.1002/ar.25558
• Hart, W.J., and Wedel, M.J. 2025. First report of neural canal ridges in fossil crocodilians. 5th Palaeontological Virtual Congress. [NB: you will probably need to be registered for 5PVC to follow that link.]