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.

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

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

So this just happened

February 24, 2022

I was on a video call with Matt, talking about a project he’s working on that involves Haplocanthosaurus. A lot of his recent project involve Haplocanthosaurus which is … an OK sauropod. I mean, it’s no brachiosaur. So this is how the conversation went:

Mike: I have bad news for you, dude. Haplocanthosaurus is only one or two nodes away from being a camarasaur.

Matt: Sure, but Haplocanthosaurus is really weird, and Camarasaurus is just basic.

Mike: Your mom’s basic.

Matt: Your mom’s one or two nodes away from being a camarasaur.

 

In mammals — certainly the most-studied vertebrates — regional differentiation of the vertebral column is distinct and easy to spot. But things aren’t so simple with sauropods. We all know that the neck of any tetrapod is made up of cervical vertebrae, and that the trunk is made up of dorsal vertebrae (subdivided into thoracic and lumbar vertebrae in the case of mammals). But how do we tell whether a given verebra is a posterior cervical or an anterior dorsal?

Here two vertabrae: a dorsal vertebra (D3) and a cervical vertebra (C13) from CM 84, the holotype of Diplodocus carnegii, modified from Hatcher (1901: plates III and VII):

It’s easy to tell these apart, even when as here we have only lateral-view images: the dorsal vertebra is tall, its centrum is short, its neural spine is anteroposteriorly compressed and its parapophysis is up on the dorsal half of the centrum; but the cervical vertebra is relatively low, its centrum is elongated, its neural spine is roughly triangular and its parapophysis hangs down well below the centrum (and has a cervical rib fused to it and the diapophysis).

But things get trickier in the shoulder region because, in sauropods at least, the transition through the last few cervicals to the first few dorsals is gradual — the vertebrae become shorter, taller and broader — and tends to have no very obvious break point. In this respect, they differ from mammals, in which the regional differentiation of the spinal column is more abrupt. (Although even here, things may not be as simple as generally assumed: for example, Gunji and Endo (2016) argued that the 1st thoracic vertebra of the giraffe behaves functionally like an 8th cervical.)

So here are those two vertebrae in context: the sequence D3 D2 D1 C15 C14 C13 in CM 84, the holotype of Diplodocus carnegii, modified from Hatcher (1901: plates III and VII):

Given that the leftmost is obviously a dorsal and the rightmost obviously a cervical, where would you place the break-point?

The most usual definition seems to be that the first dorsal vertebra is the first one that has a free rib, i.e. one not fused to the vertebra: in the illustration above, you can see that the three cervicals on the right all have their cervical ribs fused to their diapophyses and parapophyses, and the three dorsals on the left do not. This definition of the cervical/dorsal distinction seems to be widely assumed, but it is rarely explicitly asserted. (Does anyone know of a paper that lays it out for sauropods, or for dinosaurs more generally?)

But wait!

Hatcher (1903:8) — the same dude — in his Haplocanthosaurus monograph, writes:

The First Dorsal (Plate I., Fig. 1). […] That the vertebra now under consideration was a dorsal is conclusively shown not by the presence of tubercular and capitular rib facets showing that it supported on either side a free rib, for there are in our collections of sauropods, skeletons of other dinosaurs fully adult but, with the posterior cervical, bearing free cervical ribs articulating by both tubercular and capitular facets as do the ribs of the dorsal region. The character in this vertebra distinguishing it as a dorsal is the broadly expanded external border of the anterior branch of the horizontal lamina [i.e. what we would now call the centroprezygapophyseal lamina]. This element has been this modified in this and the succeeding dorsal, no doubt, as is known to be the case in Diplodocus to give greater surface for the attachment of the powerful muscles necessary for the support of the scapula.

Hatcher’s illustrations show this feature, though they don’t make it particularly obvious: here are the last two cervicals and the first dorsal, modified from Hatcher (1903:plate I), with the facet in question highlighted in pink: right lateral view at the top, then anterior, and finally posterior view at the bottom. (The facet is only visible in lateral and anterior views):

Taken at face value, Hatcher’s words here seem to imply that he considers the torso to begin where the scapula first lies alongside the vertebral column. Yet if you go back to the Diplodocus transition earlier in this post, a similar scapular facet is not apparent in the vertebra that he designated D1, and seems to be present only in D2.

Is this scapular-orientation based definition a widespread usage? Can anyone point me to other papers that use it?

Wilson (2002:226) mentions a genetic definition of the cervical/dorsal distinction

Vertebral segment identity may be controlled by a single Hox gene. The cervicodorsal transition in many tetrapods, for instance, appears to be defined by the expression boundary of the Hoxc-6 gene.

But this of course is no use in the case of extinct animals such as sauropods.

So what’s going on here? In 1964, United States Supreme Court Justice Potter Stewart, in describing his threshold test for obscenity, famously said “I shall not today attempt further to define the kinds of material I understand to be embraced within that shorthand description, and perhaps I could never succeed in intelligibly doing so. But I know it when I see it.” Is that all we have for the definition of what makes a vertebra cervicals as opposed to dorsal? We know it when we see it?

Help me out, folks! What should the test for cervical-vs-dorsal be?

References

  • Gunji, Mego, and Hideki Endo. 2016. Functional cervicothoracic boundary modified by anatomical shifts in the neck of giraffes. Royal Society Open Science 3:150604. doi:10.1098/rsos.150604
  • Hatcher, Jonathan B. 1901. Diplodocus (Marsh): its osteology, taxonomy and probable habits, with a restoration of the skeleton. Memoirs of the Carnegie Museum 1:1-63 and plates I-XIII.
  • Hatcher, J. B. 1903b. Osteology of Haplocanthosaurus with description of a new species, and remarks on the probable habits of the Sauropoda and the age and origin of the Atlantosaurus beds; additional remarks on Diplodocus. Memoirs of the Carnegie Museum 2:1-75 and plates I-VI.
  • Wilson, Jeffrey A. 2002. Sauropod dinosaur phylogeny: critique and cladistic analysis. Zoological Journal of the Linnean Society 136:217-276.

A. Recovered skeletal elements of Haplocanthosaurus specimen MWC 8028. B. Caudal vertebra 3 in right lateral view. C. The same vertebra in posterior view. Lines show the location of sections for D and E. D. Midsagittal CT slice. The arrow indicates the ventral expansion of the neural canal into the centrum. E. Horizontal CT slice at the level of the neural arch pedicles, with anterior toward the top. Arrows indicate the lateral expansions of the neural canal into the pedicles. B-E are shown at the same scale. Wedel et al. (2021: fig. 1).

New paper out today:

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 (link)

The paper is new, but the findings aren’t, particularly. They’re essentially identical to what we reported in our 1st Paleo Virtual Conference slide deck and preprint, and in the “Tiny Titan” exhibit at the Western Science Center, just finally out in a peer-reviewed journal, with better figures. The paper is open access and free to the world, and it’s short, about 1600 words, so this recap will be short, too.

A. Photograph of a 3D-printed model of the first three caudal vertebrae of Haplocanthosaurus specimen MWC 8028, including endocasts of the neural canal (yellow) and intervertebral joints (blue), in right lateral view, and with the neural canal horizontal. B. Diagram of the same vertebrae 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. 2).

John Foster and I described Museum of Western Colorado (MWC) specimen 8028, a partial skeleton of Haplocanthosaurus from Snowmass, Colorado, in late 2014. One weird thing about that specimen (although not the only weird thing) is that the neural canals of the tail vertebrae are bizarrely expanded. In most vertebrae of most critters, the neural canal is a cylindrical tunnel, but in these vertebrae the neural canals are more like spherical vacuities.

John and I didn’t know what to make of that back in 2014. But a few years later I started working with Jessie Atterholt on bird anatomy, which led me to do a little project on the whole freaking zoo of weird stuff that birds and other dinosaurs do with their neural canals, which led to the 1PVC presentation, which led to this. 

Caudal vertebra 3 of Haplocanthosaurus specimen MWC 8028 in left posterolateral (A), posterior (B), and right posterolateral (C) views, with close-ups (D and E). In A and B, a paintbrush is inserted into one of the lateral recesses, showing that the neural canal is wider internally than at either end. Wedel et al. (2021: fig. 3).

Of course there will be more posts and more yapping, as signaled by the ‘Part 1’ in the post title. Although I am extremely satisfied with the streamlined, 1600-word missile of information and reasoning that just dropped, there are parts that I want to unpack, that haven’t been unpacked before. But the paper launched at midnight-thirty, Pacific Daylight Time, I’m up way too late finishing this first post, and I reckon the rest will keep for a few hours at least.

Anatomical features of the neural canal in birds and other dinosaurs. A. MWC 9698, a mid caudal vertebra of Apatosaurus in posterodorsal view. Arrows highlight probable vascular foramina in the ventral floor of the neural canal. B. LACM 97479, a dorsal vertebra of Rhea americana in left anterolateral view. Arrows highlight pneumatic foramina inside the neural canal. C. A hemisected partial synsacrum of a chicken, Gallus domesticus, obtained from a grocery store. Anterior is to the right. The bracket shows the extent of the dorsal recess for the glycogen body, which only spans four vertebrae. Arrows highlight the transverse grooves in the roof of the neural canal for the lumbosacral organ. D. Sagittal (left) and transverse (right) CT slices through the sacrum of a juvenile ostrich, Struthio camelus. The bracket shows the extent of the lumbosacral expansion of the spinal cord. Indentations in the roof of the neural canal house the lumbosacral organ. In contrast to the chicken, the ostrich has a small glycogen body that does not leave a distinct osteological trace. Yellow arrows show the longitudinal troughs in the ventral floor of the neural canal that house the ventral eminences of the spinal cord. Wedel et al. (2021: fig. 4).

I have a ton of people to thank. John Foster, obviously, for initiating the line of research that led here. Julia McHugh for access to the MWC collections, and for being an excellent sounding board regarding the Morrison Formation, sauropod dinosaurs, and crafting ambitious but tractable research projects. Anne Weil for helping me be methodical in thinking through the logic of the paper, and Mike Taylor for helping me get it polished. Niels Bonde, Steven Jasinski, and David Martill for constructive reviews, which were published alongside the paper. We couldn’t take all of their suggestions because of space limitations, but figures 3 and 4 were born because they asked for them, and that’s not a small thing. Vicki and London Wedel for putting up with me at various points in this project, especially in the last few days as I’ve been going bonkers correcting page proofs. And finally, because I’m the one writing this blog post, my coauthors: Jessie Atterholt, Alton Dooley, Saad Farooq, Jeff Macalino, Thierra Nalley, Gary Wisser, and John Yasmer, for their contributions and for their patience during the unusually long gestation of this very short paper.

More to say about all that in the future. For now, yay, new paper. Have fun with it. Here’s the link again.

References

 

FIGURE 7.1. Pneumatic features in dorsal vertebrae of Barapasaurus (A–D), Camarasaurus (E–G), Diplodocus (H–J), and Saltasaurus (K–N). Anterior is to the left; different elements are not to scale. A, A posterior dorsal vertebra of Barapasaurus. The opening of the neural cavity is under the transverse process. B, A midsagittal section through a middorsal vertebra of Barapasaurus showing the neural cavity above the neural canal. C, A transverse section through the posterior dorsal shown in A (position 1). In this vertebra, the neural cavities on either side are separated by a narrow median septum and do not communicate with the neural canal. The centrum bears large, shallow fossae. D, A transverse section through the middorsal shown in B. The neural cavity opens to either side beneath the transverse processes. No bony structures separate the neural cavity from the neural canal. The fossae on the centrum are smaller and deeper than in the previous example. (A–D redrawn from Jain et al. 1979:pl. 101, 102.) E, An anterior dorsal vertebra of Camarasaurus. F, A transverse section through the centrum (E, position 1) showing the large camerae that occupy most of the volume of the centrum. G, a horizontal section (E, position 2). (E–G redrawn from Ostrom and McIntosh 1966:pl. 24.) H, A posterior dorsal vertebra of Diplodocus. (Modified from Gilmore 1932:fig. 2.) I, Transverse sections through the neural spines of other Diplodocus dorsals (similar to H, position 1). The neural spine has no body or central corpus of bone for most of its length. Instead it is composed of intersecting bony laminae. This form of construction is typical for the presacral neural spines of most sauropods outside the clade Somphospondyli. (Modified from Osborn 1899:fig. 4.) J, A horizontal section through a generalized Diplodocus dorsal (similar to H, position 2). This diagram is based on several broken elements and is not intended to represent a specific specimen. The large camerae in the midcentrum connect to several smaller chambers at either end. K, A transverse section through the top of the neural spine of an anterior dorsal vertebra of Saltasaurus (L, position 1). Compare the internal pneumatic chambers in the neural spine of Saltasaurus with the external fossae in the neural spine of Diplodocus shown in J. L, An anterior dorsal vertebra of Saltasaurus. M, A transverse section through the centrum (L, position 2). N, A horizontal section (L, position 3). In most members of the clade Somphospondyli the neural spines and centra are filled with small camellae. (K–N modified from Powell 1992:fig. 16.) [Figure from Wedel 2005.]

Here’s figure 1 from my 2005 book chapter. I tried to cram as much pneumatic sauropod vertebra morphology into one figure as I could. All of the diagrams are traced from pre-existing published images except the horizontal section of the Diplodocus dorsal in J, which is a sort of generalized cross-section that I based on broken centra of camerate vertebrae from several taxa (like the ones shown in this post). One thing that strikes me about this figure, and about most of the CT and other cross-sections that I’ve published or used over the years (example), is that they’re more or less bilaterally symmetrical. 

We’ve talked about asymmetrical vertebrae before, actually going back to the very first post in Xenoposeidon week, when this blog was only a month and a half old. But not as much as I thought. Given how much space asymmetry takes up in my brain, it’s actually weird how little we’ve discussed it.

The fourth sacral centrum of Haplocanthosaurus CM 879, in left and right lateral view (on the left and right, respectively). Note the distinct fossa under the sacral rib attachment on the right, which is absent on the left.

Also, virtually all of our previous coverage of asymmetry has focused on external pneumatic features, like the asymmetric fossae in this sacral of Haplocanthosaurus (featured here), in the tails of Giraffatitan and Apatosaurus (from Wedel and Taylor 2013b), and in the ever-popular holotype of Xenoposeidon. This is true not just on the blog but also in our most recent paper (Taylor and Wedel 2021), which grew out of this post.

Given that cross-sectional asymmetry has barely gotten a look in before now, here are three specimens that show it, presented in ascending levels of weirdness.

First up, a dorsal centrum of Haplocanthosaurus, CM 572. This tracing appeared in Text-fig 8 in my solo prosauropod paper (Wedel 2007), and the CT scout it was traced from is in Fig 6 in my saurischian air-sac paper (Wedel 2009). The section shown here is about 13cm tall dorsoventrally. The pneumatic fossa on the left is comparatively small, shallow, and lacks very distinct overhanging lips of bone. The fossa on the right is about twice as big, it has a more distinct bar of bone forming a ventral lip, and it is separated from the neural canal by a much thinner plate of bone. The fossa on the left is more similar to the condition in dorsal vertebrae of Barapasaurus or juvenile Apatosaurus, where as the one on the right shows a somewhat more extensive and derived degree of pneumatization. The median septum isn’t quite on the midline of the centrum, but it’s pretty stout, which seems to be a consistent feature in presacral vertebrae of Haplocanthosaurus.

 

Getting weirder. Here’s a section through the mid-centrum of C6 of CM 555, which is probably Brontosaurus parvus. That specific vert has gotten a lot of SV-POW! love over the years: it appears in several posts (like this one, this one, and this one), and in Fig 19 in our neural spine bifurcation paper (Wedel and Taylor 2013a). The section shown here is about 10cm tall, dorsoventrally. In cross-section, it has the classic I-beam configuration for camerate sauropod vertebrae, only the median septum is doing something odd — rather than attaching the midline of the bony floor of the centrum, it’s angled over to the side, to attach to what would normally be the ventral lip of the camera. I suspect that it got this way because the diverticulum on the right either got to the vertebra a little ahead of the one on the left, or just pneumatized the bone faster, because the median septum isn’t just bent, even the vertical bit is displaced to the left of the midline. I also suspect that this condition was able to be maintained because the median septa weren’t that mechanically important in a lot of these vertebrae. We use “I-beam” as a convenient shorthand to describe the shape, but in a metal I-beam the upright is as thick or thicker than the cross bits. In contrast, camerate centra of sauropod vertebrae could be more accurately described as a cylinders or boxes of bone with some holes in the sides. I think the extremely thin median septum is just a sort of developmental leftover from the process of pneumatization.

EDIT 3 days later: John Whitlock reminded me in the comments of Zurriaguz and Alvarez (2014), who looked at asymmetry in the lateral pneumatic foramina in cervical and dorsal vertebrae of titanosaurs, and found that consistent asymmetry along the cervical column was not unusual. They also explicitly hypothesized that the asymmetry was caused by diverticula on one side reaching the vertebrae earlier than diverticula on other other side. I believe they were the first to advance that idea in print (although I should probably take my own advice and scour the historical literature for any earlier instances), and needless to say, I think they’re absolutely correct.

Both of the previous images were traced from CTs, but the next one is traced from a photo of a specimen, OMNH 1882, that was broken transversely through the posterior centrum. To be honest, I’m not entirely certain what critter this vertebra is from. It is too long and the internal structure is too complex for it to be Camarasaurus. I think an apatosaurine identity is unlikely, too, given the proportional length of the surviving chunk of centrum, and the internal structure, which looks very different from CM 555 or any other apatosaur I’ve peered inside. Diplodocus and Brachiosaurus are also known from the Morrison quarries at Black Mesa, in the Oklahoma panhandle, which is where this specimen is from. Of those two, the swoopy ventral margin of the posterior centrum looks more Diplodocus-y than Brachiosaurus-y to me, and the specimen lacks the thick slab of bone that forms the ventral centrum in presacrals of Brachiosaurus and Giraffatitan (see Schwarz and Fritsch 2006: fig. 4, and this post). So on balance I think probably Diplodocus, but I could easily be wrong.

Incidentally, the photo is from 2003, before I knew much about how to properly photograph specimens. I really need to have another look at this specimen, for a lot of reasons.

Whatever taxon the vertebra is from, the internal structure is a wild scene. The median septum is off midline and bent, this time at the top rather than the bottom, the thick ventral rim of the lateral pneumatic foramen is hollow on the right but not on the left, and there are wacky chambers around the neural canal and one in the ventral floor of the centrum. 

I should point out that no-one has ever CT-scanned this specimen, and single slices can be misleading. Maybe the ventral rim of the lateral foramen is hollow just a little anterior or posterior to this slice. Possibly the median septum is more normally configured elsewhere in the centrum. But at least at the break point, this thing is crazy. 

What’s it all mean? Maybe the asymmetry isn’t noise, maybe it’s signal. We know that when bone and pneumatic epithelium get to play together, they tend to make weird stuff. Sometimes that weirdness gets constrained by functional demands, other times not so much. I think it’s very seductive to imagine sauropod vertebrae as these mechanically-optimized, perfect structures, but we have other evidence that that’s not always true (for example). Maybe as long as the articular surfaces, zygapophyses, epipophyses, neural spine tips, and cervical ribs — the mechanically-important bits — ended up in the right places, and the major laminae did a ‘good enough’ job of transmitting forces, the rest of each vertebra could just sorta do whatever. Maybe most of them end up looking more or less the same because of shared development, not because it was so very important that all the holes and flanges were in precisely the same places. That might explain why we occasionally get some really odd verts, like C11 of the Diplodocus carnegii holotype.

That’s all pretty hand-wavy and I haven’t yet thought of a way to test it, but someone probably will sooner or later. In the meantime, I think it’s valuable to just keep documenting the weirdness as we find it.

References

Can I really be the first one to have done this? Seems unlikely. Sing out in the comments if you’ve seen others.

Anyway, folks, here’s your new all-purpose scale silhouette. Useful fact: the standard metal folding chairs found from sea to shining sea are 29.25 inches tall, or 0.75 meters. Bernie might be in a plastic folding chair here, I dunno, I’m no expert. But folding chair seats are typically 16-17 inches off the ground, so it can’t be that far out.

Who will get Bernie into print first?

If you’re thinking that it’s about time to look at some sauropod vertebrae from the Salt Wash member of the Morrison Formation, well, you’re gol-durned right, pardner. Let’s ride.

Here’s a vertebra sticking out of the rock. For once it’s not in cross-section. We’re simply looking at the posterior surface of a dorsal vertebra and bits of its associated ribs. Let’s stand it up correctly:

And, well, heck, Alex, I’d like to go ahead and solve the puzzle:

Figure on the right from Wedel and Taylor (2013a), and composed in turn from plates in Hatcher (1901, Diplodocus), Hatcher (1903, Haplocanthosaurus), and Gilmore (1936, Apatosaurus).

UPDATE: I had the discovery sequence wrong–this is one of the bones that was first found by photographer Guy Tal, who then put ReBecca Hunt-Foster onto the area. ReBecca has since gone on to become Monument Paleontologist at Dinosaur National Monument, but at the time she was working as a BLM paleontologist out of the Moab office. ReBecca then brought out some more of us out to take a look, and that was the genesis of my work with her and John in the Salt Wash.

John Foster and Cary Woodruff were both there when I saw this vertebra for the first time. I think we set a new record for a consensus among paleontologists in concluding that this vertebra belongs to Haplocanthosaurus. The super-tall, cathedral-esque laminae arching over the neural canal and the up-tilted transverse processes are absolutely diagnostic, and not present in any other Morrison sauropods. Haplocanthosaurus is one of the rarer sauropods in the Morrison, so it’s nice to have one in our Salt Wash fauna. Not least because of all the other awesome sauropods out there, it’s this weird little duck that my destiny seems to have become intertwingled with (exhibits A, B, C, D, E, and counting).

Speaking of: did you remember that the Western Science Center exhibit on the Snowmass Haplocanthosaurus is still up for a couple more months? Have you seen it? Go see it!

Life restoration of Haplocanthosaurus by Brian Engh, for the Western Science Center exhibit.

So, hey, rock and roll, we have Haplocanthosaurus, and that is legitimately exciting. Between that and Camarasaurus (covered here) we have the primitive-and-unspecialized end of the Morrison sauropods sewn up. Anything bigger or more exotic? Why, yes, in fact. Stay tuned.

This is another “Road to Jurassic Reimagined, Part 2″ post. You know the drill: Part 1 is here, Part 2 will be going up here in the near future, Part 3 will be along sometime after that.

References

A life-size silhouette of the Snowmass Haplocanthosaurus, with Thierra Nalley, me, and Jessie Atterholt for scale. Photo by Jeremiah Scott.

Tiny Titan, a temporary exhibit about the Snowmass Haplocanthosaurus project, opened at the Western Science Center in Hemet, California, last night. How? Why? Read on.

Things have been quieter this year on the Haplo front than they were in 2018, for many reasons. My attention was pulled away by a lot of teaching and other day-job work–we’re launching a new curriculum at the med school, and that’s eaten an immense amount of time–and by some very exciting news from the field that I can’t tell you about quite yet (but watch this space). Things are still moving, and there will be a paper redescribing MWC 8028 and all the weird and cool things we’ve learned about it, but there are a few more timely things ahead of it in the queue.

One of the things going on behind the scenes this year is that Jessie Atterholt, Thierra Nalley, and I have been working with Alton Dooley, the director of the Western Science Center, on this exhibit. Alton has had a gleam in his eye for a long time of using the WSC’s temporary exhibit space to promote the work of local scientists, and we had the honor of being his first example. He also was not fazed by the fact that the project isn’t done–he wants to show the public the process of science in all of its serendipitous and non-linear glory, and not just the polished results that get communicated at the end.

Everything’s better cut in half. Photo by Jessie Atterholt.

Which is not to say that the exhibit isn’t polished. On the contrary, it looks phenomenal. Thanks to a loan from Julia McHugh at Dinosaur Journey in Colorado, most of the real fossils are on display. We’re only missing the ribs and most of the sacrum, which is too fragmentary and fragile to come out of its jacket. As you can see from the photo up top, there is a life-size vinyl silhouette of the Snowmass Haplo, with 3D prints of the vertebrae in approximate life position. Other 3D prints show the vertebrae before and after the process of sculpting, rescanning, and retrodeformation, as described in our presentation for the 1st Palaeontological Virtual Congress last year (that slideshow is a PeerJ Preprint, here). The exhibit also includes panels on “What is Haplocanthosaurus” and its relationships, on pneumaticity in sauropods, on the process of CT scanning and 3D modeling, and on the unusual anatomical features of the Snowmass specimen. The awesome display shown above, with the possibly-bumpy spinal cord and giant intervertebral discs reconstructed, was all Alton–he did the modeling, printing, and assembly himself.

Haplo vs Bronto. Thierra usually works on the evolution and development of the vertebral column in primates, so I had to show her how awesome vertebrae can be when they’re done right. Photo by Brittney Stoneburg.

My favorite thing in the exhibit is this striking comparison of one the Snowmass Haplo caudals with a proximal caudal from the big Oklahoma apatosaurine. This was Alton’s idea. He asked me if I had any photos of caudal vertebrae from really big sauropods that we could print at life size to compare to MWC 8028, and my mind went immediately to OMNH 1331, which is probably the second-largest-diameter vertebra of anything from all of North America (see the list here). It was also Alton’s idea to fill in the missing bits using one of Marsh’s plates of Brontosaurus excelsus from Como Bluff in Wyoming. It’s a pretty amazing display, and it turns out to have been a vehicle for discovery, too–I didn’t realize until I saw the verts side-by-side that the neural canal of the Snowmass Haplo caudal is almost as big as the neural canal from the giant apatosaurine caudal. It’s not a perfect comparison, because the OMNH fossil doesn’t preserve the neural canal, and the Como specimen isn’t that big, but proportionally, the Snowmass Haplo seems to have big honkin’ neural canals, not just at the midpoint (which we already knew), but all the way through. Looks like I have some measuring and comparing to do.

(Oh, about the title: we don’t know if the Snowmass Haplo was fully grown or not, but not all haplocanthosaurs were small. The mounted H. delfsi in Cleveland is huge, getting into Apatosaurus and Diplodocus territory. Everything we can assess in the Snowmass Haplo is fused, for what that’s worth. We have some rib chunks and Jessie will be doing histo on them to see if we can get ontogenetic information. I’ll keep you posted.)

Brian’s new Haplocanthosaurus restoration, along with some stinkin’ mammals. Photo by Jessie Atterholt.

Brian Engh contributed a fantastic life restoration of Haplocanthosaurus pro bono, thanks to this conversation, which took place in John Foster’s and ReBecca Hunt-Foster’s dining room about a month ago:

Brian: What are you drawing?

Me: Haplocanthosaurus.

Brian: Is that for the exhibit?

Me: Yup.

Brian (intense): Dude, I will draw you a Haplocanthosaurus.

Me: I know, but you’re a pro, and pros get paid, and we didn’t include a budget for paleoart.

Brian (fired up): I’m offended that you didn’t just ask me to draw you a Haplocanthosaurus.

Then he went to the Fosters’ couch, sat down with his sketchbook, and drew a Haplocanthosaurus. Not only is it a stunning piece on display in the exhibit, there are black-and-white printouts for kids to take and color (or for adults to take to their favorite tattoo artists, just sayin’). [Obligatory: this is not how things are supposed to work. We should all support original paleoart by supporting the artists who create it. But Brian just makes so damn many monsters that occasionally he has to kick one out for the heck of it. Also, I support him on Patreon, and you can, too, so at a stretch you could consider this the mother of all backer rewards.]

One special perk from the opening last night: Jessica Bramson was able to attend. Who’s that, you ask? Jessica’s son, Mike Gordon, found the first piece of bone from the Snowmass Haplo on their property in Colorado over a decade ago. Jessica and her family spent two years uncovering the fossils and trying to get paleontologists interested. In time she got in touch with John Foster, and the rest is history. Jessica lives in California now, and thanks to John’s efforts we were able to invite her to the exhibit opening to see her dinosaur meet the world. Stupidly, I did not get any photos with her, but I did thank her profusely.

A restored, retrodeformed caudal of the Snowmass Haplocanthosaurus, 3D-printed at life size for the exhibit. Photo swiped from the WSC Facebook page.

I owe a huge thanks to Alton Dooley for taking an interest in our work, and to the whole WSC crew for their hard work creating and promoting the exhibit. You all rock.

The exhibit will run through the end of March, 2020, at least. I deliberately did not show most of it, partly because I was too busy having fun last night to be diligent about taking photos, but mostly because I want you to go see it for yourself (I will do a retrospective post with more info after the exhibit comes down, for people who weren’t able to see it in person). If you make it out to Hemet, I hope you have half as much fun going through the exhibit as we did making it.