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

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

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

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

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

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

References

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The afternoon of Day 1 at TetZooCon 2018 was split into two parallel streams: downstairs, some talks that I would have loved to see; and upstairs, a palaeoart workshop that I was even keener not to miss out on.

There were talks by Luis Rey (on how palaeoart has had to be dragged kicking and screaming into accepting feathers and bright colours) and by Mark Witton (on the future of palaeoart — sadly, bereft of slides). Both fascinating.

But better still was the wide-ranging informal discussion between Luis, Mark, John Conway, Bob Nicholls and others on what palaeoart is actually all about. For Luis, it’s basically fun; for Mark, it’s primarily science communication; for John, it’s art first, and palaeontology only because that’s what he happens to be depicting; and for Bob, as well as all those things, it’s crucially important as a job of work, satisfying the requirements of those who commission that work. Obviously that’s a huge over-simplification: all of them have all these aspects going on in varying proportions. But that’s how I read it.

At the same time that all this was going on, we — maybe 60 or 70 of us? — were encouraged to create our own art, either attempting styles that are different to what we usually do, are using materials we’re not so familiar with. For the many excellent artists in the group, this challenge must have been interestingly novel. For non-artists like myself, it was just a chance to play.

I took the opportunity to try my hand with charcoal, in the hope of getting some suggestive or even impressionistic textures. Here’s my first work — an indeterminate brachiosaur with an inexplicably big head.

Aside from the head — I can’t do heads! — I’m reasonably happy with that. I got a decent sense of bulk in the torso, anyway.

Encouraged, I made a start on a second piece: a BRONTOSMASH!ing apatosaur that didn’t come out so well.

I’m happy with the forelimbs here, but something is dreadfully wrong with the torso and I can’t put a finger on what it is. If I’d had more time, I’d have put in the second hindlimb, which might have helped me figure out what was going wrong. The other thing I fluffed here was that I should have made the neck even fatter and more robust. Oh, and of course the head. I might return to this and see if I can sort out, if I can find some charcoal.

Anyway, it was a fascinating experience. And it’s left me with a new favourite art medium.

 

WOW! I knew I was dragging a bit on getting around to this vertebral orientation problem, but I didn’t realize a whole month had passed. Yikes. Thanks to everyone who has commented so far, and thanks to Mike for getting the ball rolling on this. Previous posts in this series are here and here.

First up, this may seem like a pointlessly picky thing to even worry about. Can’t we just orient the vertebrae in whichever way feels the most natural, or is easiest? Do we have to think about this?

The alarmingly 3D pelvis of the mounted brontosaur at the AMNH. Note that sauropod pubes are usually illustrated lying flat, so what usually passes for ‘lateral’ view would be roughly from the point of view of the animal’s knee.

I think we do. For sauropods, vertebrae are usually oriented for illustration purposes in one of two ways. The first is however they sit most easily on their pallets. This is similar to the problem Mike and I found for ‘lateral’ views of sauropod pelvic elements when were on our AMNH/Yale trip in 2012. In an articulated skeleton, the pubes and ischia usually lean inward by 30-45 degrees from their articulations with the ilia, so they can meet on the midline, but when people illustrate the “lateral view” of a sauropod pubis or ischium, it’s often the ventro-lateral aspect that is face-up when the element is lying on a shelf or a pallet. Photographic lateral does not equal biological lateral for those elements. Similarly, if I’m trying to answer biological questions about vertebrae (see below), I need to know something about their orientation in the body, not just how they sit comfortably on a pallet.

The other way that vertebrae are commonly oriented is according to what we might call the “visual long axis” of the centrum—so for example, dorsoventrally tall but craniocaudally short proximal caudals get oriented with the centrum ‘upright’, whereas dorsoventrally short but craniocaudally long distal caudals get oriented with the centrum ‘horizontal’, even if they’re in the same tail and doing so makes the neural canals or articular faces be oriented inconsistently down the column. (I’m not going to name names, because it seems mean to pick on people for something I just started thinking about myself, but if you go plow through a bunch of sauropod descriptions, you’ll see what I’m talking about.)

Are there biological questions where this matters? You bet! There are some questions that we can’t answer unless we have the vertebrae correctly oriented first. One that comes to mind is measuring the cross-sectional area of the neural canal, which Emily Giffin did a lot of back in the 90s. Especially for the Snowmass Haplocanthosaurus, what counts as the cross-sectional area of the neural canal depends on whether we are looking at the verts orthogonal to their articular faces, or in alignment with the course of the canal. I think the latter is pretty obviously the way to go if we are measuring the cross-sectional area of the canal to try and infer the diameter of the spinal cord—we’d want to see the canal the same way the cord ‘sees’ it as it passes through—but it’s less obvious if we’re measuring, say, the surface area of the articular face of the vertebra to figure out, say, cartilage stress. It doesn’t seem unreasonable to me that we might want to define a ‘neural axis’ for dealing with spinal-cord-related questions, and a ‘biomechanical axis’ for dealing with articulation-related questions.

Caudal 3 of the Snowmass Haplocanthosaurus, hemisected 3D model.

With all that in mind, here are some points.

To me, asking “how do we know if a vertebra is horizontal” is an odd phrasing of the problem, because “horizontal” doesn’t have any biological meaning. I think it makes more sense to couch the question as, “how do we define cranial and caudal for a vertebra?” Normally both the articular surfaces and the neural canal are “aimed” head- and tail-wards, so the question doesn’t come up. Our question is, how do we deal with vertebrae for which the articular surfaces and neural canal give different answers?

For example. Varanus komodoensis caudal.

(And by the way, I’m totally fine using “anterior” and “posterior” for quadrupedal animals like sauropods. I don’t think it causes any confusion, any more than people are confused by “superior” and “inferior” for human vertebrae. But precisely because we’re angling for a universal solution here, I think using “cranial” and “caudal” makes the most sense, just this once. That said, when I made the image above, I used anterior and posterior, and I’m too lazy now to change it.)

I think if we couch the question as “how do we define cranial and caudal”, it sets up a different set of possible answers than Mike proposed in the first post in this series: (1) define cranial and caudal according to the neural canal, and then describe the articular surfaces as inclined or tilted relative to that axis; (2) vice versa—realizing that using the articular surfaces to define the anatomical directions may admit a range of possible solutions, which might resurrect some of the array of possible methods from our first-draft abstract; (3) define cranial and caudal along the long axis of the centrum, which is potentially different from either of the above; (4) we can imagine a range of other possibilities, like “use the zygs” or “make the transverse processes horizontal” (both of which are subsets of Mike’s method C) but I don’t think most of those other possibilities are sufficiently compelling to be worthy of lengthy discussion.

IF we accept “neural canal”, “articular surfaces”, and “centrum long axis” as our strongest contenders, I think it makes most sense to go with the neural canal, for several reasons:

  • In a causative sense, the neural tube/spinal cord does define the cranial/caudal axis for the developing skeleton. EDIT: Actually, that’s a bit backwards. It’s the notochord, which is later replaced by the vertebral column, that induces the formation of the brain and spinal cord from the neural plate. But it’s still true that the vertebrae form around the spinal cord, so it’s not wrong to talk about the spinal cord as a defining bit of soft tissue for the developing vertebrae to accommodate.
  • The neural canal works equally well for isolated vertebrae and for articulated series. Regardless of how the vertebral column is oriented in life, the neural canal is relatively smooth—it may bend, but it doesn’t kink. So if we line up a series of vertebrae so that their neural canals are aligned, we’re probably pretty close to the actual alignment in life, even before we look at the articular surfaces or zygs.
  • The articulated tails of Opisthocoelicaudia and big varanids show that sometimes the articular surfaces simply are tilted to anything that we might reasonably consider to be the cranio-caudal axis or long axis of the vertebra. In those cases, the articular surfaces aren’t orthogonal to horizontal OR to cranio-caudal. So I think articular surfaces are ruled out because they break down in the kinds of edge cases that led us to ask the question in the first places.

Opistocoelicaudia caudals 6-8, stereopair, Borsuk-Bialynicka (1977:plate 5).

“Orient vertebrae, isolated or in series, so that their neural canals define the cranio-caudal axis” may seem like kind of a ‘duh’ conclusion (if you accept that it’s correct; you may not!), but as discussed up top, often vertebrae from a single individual are oriented inconsistently in descriptive works, and orientation does actually matter for answering some kinds of questions. So regardless of which conclusion we settle on, there is a need to sort out this problem.

That’s where I’m at with my thinking. A lot of this has been percolating in my hindbrain over the last few weeks—I figured out most of this while I was writing this very post. Is it compelling? Am I talking nonsense? Let me know in the comments.

Well, that didn’t take long. Earlier today, my subterranean hacker collective released thousands of emails exchanged by Mike Taylor and Brian Engh, which touched on numerous issues of national and global security. Of most interest to SV-POW! readers will be this correspondence from just a few hours ago:

– – – – – – – – – – – – – – – – – – – – – – – –

Mike: Artwork attached. [Scroll down to see Mike’s submission.–MJW]

Brian: NAILED IT.

I haven’t been responding here to entrants but i feel pretty safe calling this one the winner already. Thank you for submitting. We can now sit back and laugh as all the other feeble entrants squabble knowing that you’ve already got this one in the bag.

Mike: Thanks, Brian. I hesitated before submitting this, thinking it might not be fair to up-and-coming artists who need the win more than I do; but in the end, I decided that was patronising. If they’re going to win the prize, they have to beat me on merit. You never know: it could happen.

– – – – – – – – – – – – – – – – – – – – – – – –

So, it looks like Brian has made his decision and the contest is effectively over. Although Mike says that someone else winning the contest “could happen”, Brian’s already signaled his intention to “laugh as all the other feeble entrants squabble”, which hardly sounds like he’s going to be giving anyone else a fair shake.

In Brian’s defense, the art that Mike submitted is glorious:

So complex and subtle is this work, so playful in its blending of traditional and cutting-edge thinking, so packed with detail, life history, and sheer emotion, that I feel certain that it will usher in a new era of paleoart as the dominant aesthetic expression on this planet.

Still, I don’t see how #TheSummonENGH2018 is going to survive the inevitable scandal of having a winner secretly chosen on the second day of the contest. I’m torn between towering admiration for my friends and colleagues, and fear for the rifts this may cause in the paleoart community.

I’ve reached out to representatives of both Mike and Brian for comment, and I’ll keep you updated on this developing story as more information becomes available.

Diplodocus goes digital

August 21, 2018

No time for a proper post, so here’s a screenshot from Amira of Diplodocus caudal MWC 8239 (the one you saw being CT scanned last post) about to be digitally hemisected. Trust me, you’ll want to click through for the big version. Many thanks to Thierra Nalley for the Amira help.

Further bulletins as time and opportunity allow.

John Yasmer, DO (right) and me getting ready to scan MWC 8239, a caudal vertebra of Diplodocus on loan from Dinosaur Journey, at Hemet Valley Imaging yesterday.

Alignment lasers – it’s always fun watching them flow over the bone as a specimen slides through the tube (for alignment purposes, obviously, not scanning – nobody’s in the room for that).

Lateral scout. I wonder, who will be the first to correctly identify the genus and species of the two stinkin’ mammals trailing the Diplo caudal?

A model we generated at the imaging center. This is just a cell phone photo of a single window on a big monitor. The actual model is much better, but I am in a brief temporal lacuna where I can’t screenshot it.

What am I doing with this thing? All will be revealed soon.

I was back in Utah the week before last, looking for monsters with Brian Engh and Jessie Atterholt. It was a successful hunt – more about that another time.

We made a run to Fruita, Colorado, to visit Dinosaur Journey. I was just there in May, picking up Haplocanthosaurus caudals for CT scanning (and other fun things). We picked up another specimen this time, for a different project – more on that in another post, too.

Not this one, but like this one. An apatosaurine middle caudal vertebra, MWC 5742, in left lateral view.

There’s a nice ceratopsian exhibit up at Dinosaur Journey right now, with cast skulls from many of the new ceratopsians that have been described in the past couple of decades. My near-favorites were Zuniceratops and Diabloceratops, both of which are small enough that they must have been adorable in life (think pony-sized and big-horse-sized, respectively).

My absolute favorite, of course, was this little thing:

I can tell you exactly how Aquilops came to be on display there. Julia McHugh printed a copy of the holotype, because it’s freely available to the world. And she used Brian’s Aquilops head recon in the signage (correctly, with attribution), because it’s also freely available to the world. In fact, I’ve seen Aquilops on display at several museums now for just those reasons. So, folks, if you want your critters to be seen, make them open. Hiring a paleoartist to do some awesome artwork that can be released under a CC-BY license (because you paid them, not because you asked them to give their art away for “exposure”) is a huge help.

We had to geek out a little about unexpectedly finding ‘our’ dinosaur on display:

But of course it is not our dinosaur anymore – that’s the whole point. Aquilops belongs to the world.

For more on our trip, see Jessie’s posts herehere, and here.