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

This just in from John Conway:

John doesn’t say much about it in the tweet where he unveiled this piece: just “A new #painting, of a Saltapotamus”. His website is just a little more forthcoming:

Saltapotamus

Saltasaurus was a small (for a sauropod) sauropod from the Late Cretaceous of Argentina. It had a some armour, and a lot of girth.

This reminds me very strongly of Obesethocoelicaudia, a fat restoration of Opisthocoelicaudia that John kindly did for Matt and me to use in our 2014 SVPCA talk, “Slender Giants”:

(Saltasaurus and Opisthocoelicaudia are both derived titanosaurs, and in most phylogenies they come out as pretty closely related.)

Is this kind of restoration credible? After all, it’s a long way from how we’ve been used to seeing Saltasaurus. Here, for example, is how E. Guanuco restored a group of four Saltasaurus individuals in Powell (2003: plate 78):

In this illustration they are tubby in a Normanpedia kind of way, but nothing very different from how (say) Apatosaurus was being restored not too long before then.

But the truth is that lots of animals have flesh envelopes very different from what you might predict based on the skeleton alone. Exhibit A, the inspiration for John’s new piece: the humble hippopotamus. Skeleton:

And life appearance:

It seems more than reasonable that across a clade as diverse, disparate and long-lived as the sauropods, there would have been some that were similarly heavy with flesh. In fact, I think it would be special pleading to argue that there were not.

Which specific sauropods were obese? That is much harder to tell. Hippos can be very heavy with little penalty as they spend much of their time in the water. Perhaps the same was true of some sauropods. If that’s so, then our quest must be for sauropods whose skeletons show adaptations for a semi-aquatic lifestyle, and on that basis Opisthocoelicaudia may have at least two feature supporting this interpretation: very robust limb bones and (if the interpretation of Borsuk-Bialynicka 1977: figure 5 is to be trusted) a transversely broad torso.

References

  • Powell, Jaime E. 2003. Revision of South American Titanosaurid dinosaurs: palaeobiological, palaeobiogeographical and phylogenetic aspects. Records of the Queen Victoria Museum 111:1-94.

 

When I was nine, a copy of Don Glut’s The New Dinosaur Dictionary turned up in my local Waldenbooks. It wasn’t my first dinosaur book, by far – I’d been a dinosaurophile since the age of three. But The New Dinosaur Dictionary was different.

Up to that point, I had subsisted on a heavy diet of kids’ dino books and the occasional article in National Geographic and Ranger Rick. The kids’ books were aimed at kids and the magazine articles were pitched at an engagingly popular level. I didn’t understand every word, but they were clearly written for curious layfolk, not specialists.

A typical spread from The New Dinosaur Dictionary (Glut, 1982). The armored sauropod blew my young mind.

The New Dinosaur Dictionary was something else entirely. It had photos of actual dinosaur bones and illustrations of skeletons with cryptic captions like, “Skeleton of Daspletosaurus torosus. (After Russell)”. Okay, clearly this Russell cove was out there drawing dinosaur skeletons and this book had reproduced some of them. But nobody I knew talked like that, and the books I had access to up to that point held no comparable language.

The New Dinosaur Dictionary (Glut, 1982: p. 271)

Then there was stuff like this: “The so-called Von Hughenden sauropod restored as a brachiosaurid by Mark Hallett”. A chain of fascinating and pleasurable ideas detonated in my brain. “The so-called” – say what now? Nobody even knew what to call this thing? Somehow I had inadvertently sailed right to the edge of human knowledge of dinosaurs, and was peering out into taxa incognita. “Restored as a brachiosaurid” – so this was just one of several possible ways that the animal might have looked. Even the scientists weren’t sure. This was a far cry from the bland assurances and blithely patronizing tones of all my previous dinosaur books.

“By Mark Hallett.” I didn’t know who this Hallett guy was, but his art was all over the book, along with William Stout and some guy named Robert T. Bakker and a host of others who were exploding my conception of what paleo art could even be. Anyway, this Mark Hallett was someone to watch, not only because he got mentioned by name a lot, but because his art had a crisp quality that teetered on some hypercanny ridge between photorealism and scribbling. His sketches looked like they might just walk off the page.

In case that line about scribbling sounds dismissive: I have always preferred sketches by my favorite artists to their finished products. The polished works are frequently inhumanly good. They seem to have descended in a state of completed perfection from some divine realm, unattainable by mere mortals. Whereas sketches give us a look under the hood, and show how a good artist can conjure light, shadow, form, weight, and texture from a few pencil strokes. Put it this way: I am anatomist by temperament first, and by training and occupation second. Of course I want to see how things are put together.

The New Dinosaur Dictionary (Glut, 1982: p. 75)

Anyway, The New Dinosaur Dictionary was something completely new in my experience. It wasn’t aimed at kids and written as if by kids, like lots of kids’ books. It wasn’t even written by adults talking down (deliberately or inadvertently) to kids, or trying to reach a wide audience that might include kids. It was written by an adult, aiming at other adults. And it was admitting in plain language that we didn’t know everything yet, that there were lots of animals trembling on the outer threshold of scientific knowledge. I didn’t understand half of it – I was down in an ontogenetic trench, looking up as these packets of information exploded like fireworks over my head.

In Seeing In the Dark, the best book about why you should go out stargazing for yourself, Timothy Ferris writes about growing up on Florida’s Space Coast in the early 1960s, and watching the first generation of artificial satellites pass overhead:

I felt like an ancient lungfish contemplating the land from the sea. We could get up there.

That’s precisely the effect that The New Dinosaur Dictionary had on me: I could get up there. Maybe not immediately. But there were steps, bodies of knowledge that could be mastered piecemeal, and most of all, mysteries to be resolved. The book itself was like a sketch, showing how from isolated and broken bones and incomplete skeletons, scientists and artists reconstructed the world of the past, one hypothesis at a time. Now I take it for granted, because I’ve been behind the curtain for a couple of decades. But to my 9-year-old self, it was revolutionary.

This has all come roaring back because of something that came in the mail this week. Or rather, something that had been waiting in the mailroom for a while, that I finally picked up this week: a package from Mark Hallett, enclosing a copy of his 2018 dinosaur calendar. And also this:

 

An original sketch, which he gave to me as a Christmas present. The published version appears on one of the final pages of our book, where we discuss the boundaries between the known – the emerging synthesis of sauropod biology that we hoped to bring to a broader audience by writing the book in the first place – and the unknown – the enduring mysteries that Mark and I think will drive research in sauropod paleobiology for the next few decades. Presented without a caption or commentary, the sketch embodies sauropods as we see them: emerging from uncertainty and ignorance one hard-won line at a time, with ever-increasing solidity.

Thank you, Mark, sincerely. That sketch, what it evokes, both for me now and for my inner 9-year-old – you couldn’t have chosen a better gift. And I couldn’t be happier. Except perhaps to someday learn that our book exploded in the mind of a curious kid the way that The New Dinosaur Dictionary did for me 34 years ago, a time that now seems as distant and romantic as the primeval forests of the Mesozoic.

This just in, from Zurriaguz and Powell’s (2015) hot-off-the-press paper describing the morphology and pneumatic features of the presacral column of the derived titanosaur Saltasaurus. (Thanks to Darren for bringing this paper to my attention.)

Now, as everyone knows, titanosaurs don’t have epipophyses. In fact, they’re the one major sauropod group where Matt has not observed them.

Until today.

Zurriaguz and Powell (2015:figure 3B). Anterior cervical vertebra PVL 4017-3 of Saltasaurus loricatus, in dorsal view (rotated 90° from the paper)

Zurriaguz and Powell (2015:figure 3B). Anterior cervical vertebra PVL 4017-3 of Saltasaurus loricatus, in dorsal view (rotated 90° from the paper)

Look at the left postzygapophysis, at top left of this image. Doesn’t that look like there’s a distinct rounded eminence sticking out towards the camera?

No? Not convinced? All right, then, how about this?

Zurriaguz and Powell (2015:figure 4B). Mid-anterior cervical PVL 4017-138 of Saltasaurus loricatus in right lateral view.

Zurriaguz and Powell (2015:figure 4B). Mid-anterior cervical PVL 4017-138 of Saltasaurus loricatus in right lateral view.

This time, look at the right postzyg (again at top left in the image). Doesn’t that look like there are two separate bony structures up there separated by a notch? A postzygapophyseal facet below, and an epipophysis above? Right?

Huh? What’s that? Just damage, you say?

All right. Let’s bring out the smoking gun.

Zurriaguz and Powell (2015:figure 5). Last anterior cervical vertebra (PVL 4017-5) of Saltasaurus loricatus in right lateral view. (Ignore the inset square for our purposes: it's in the original.)

Zurriaguz and Powell (2015:figure 5). Last anterior cervical vertebra (PVL 4017-5) of Saltasaurus loricatus in right lateral view. (Ignore the inset square for our purposes: it’s in the original.)

Again up at top left, we seem to have a clear case of a ventrally directed postzygapophyseal facet surmounted by a separate eminence which can only be an epipophysis. It even seems to be roughened for tendon attachment.

What does this mean? Only the same thing we said last time: The more we look for epipophyses, the more we find them. Amazing how often that turns out to be true of various things.

We seem to be headed towards the conclusion that epipophyses, while never ubiquitous, pop up in all sorts of places scattered all across the ornithodiran tree, encompassing birds, other theropods, sauropods, prosauropods, several groups of ornithischians, and both pterodactyloid and “rhamphorhynchoid” pterosaurs.

But what about outside Ornithodira?

Can we find epipophyses even out there, in the wilderness?

Stay tuned!

References

Caudal pneumaticity in saltasaurines. Cerda et al. (2012: fig. 1).

Earlier this month I was amazed to see the new paper by Cerda et al. (2012), “Extreme postcranial pneumaticity in sauropod dinosaurs from South America.” The title is dramatic, but the paper delivers the promised extremeness in spades. Almost every figure in the paper is a gobsmacker, starting with Figure 1, which shows pneumatic foramina and cavities in the middle and even distal caudals of Rocasaurus, Neuquensaurus, and Saltasaurus. This is most welcome. Since the 1990s there have been reports of saltasaurs with “spongy bone” in their tail vertebrae, but it hasn’t been clear until now whether that “spongy bone” meant pneumatic air cells or just normal marrow-filled trabecular bone. The answer is air cells, loads of ’em, way farther down the tail than I expected.

Caudal pneumaticity in diplodocines. Top, transverse cross-section through an anterior caudal of Tornieria, from Janensch (1947: fig. 9). Bottom, caudals of Diplodocus, from Osborn (1899: fig. 13).

Here’s why this is awesome. Lateral fossae occur in the proximal caudals of lots of neosauropods, maybe most, but only a few taxa go in for really invasive caudal pneumaticity with big internal chambers. In fact, the only other sauropod clade with such extensive pneumaticity so far down the tail are the diplodocines, including Diplodocus, Barosaurus, and Tornieria. But they do things differently, with BIG, “pleurocoel”-type foramina on the lateral surfaces of the centra, leading to BIG–but simple–camerae inside, and vertebral cross-sections that look like I-beams. In contrast, the saltasaurines have numerous small foramina on the centrum and neural arch that lead to complexes of small pneumatic camellae, giving their vertebrae honeycomb cross-sections. So caudal pneumaticity in diplodocines and saltsaurines is convergent in its presence and extent but clade-specific in its development. Pneumaticity doesn’t get much cooler than that.

Pneumatic ilia in saltasaurines. Cerda et al. (2012: fig. 3).

But it does get a little cooler. Because the stuff in the rest of the paper is even more mind-blowing. Cerda et al. (2012) go on to describe and illustrate–compellingly, with photos–pneumatic cavities in the ilia, scapulae, and coracoids of saltasaurines. And, crucially, these cavities are connected to the outside by pneumatic foramina. This is important. Chambers have been reported in the ilia of several sauropods, mostly somphospondyls but also in the diplodocoid Amazonsaurus. But it hasn’t been clear until now whether those chambers connected to the outside. No patent foramen, no pneumaticity. It seemed unlikely that these sauropods had big marrow-filled vacuities in their ilia–as far as I know, all of the non-pneumatic ilia out there in Tetrapoda are filled with trabecular bone, and big open marrow spaces only occur in the long bones of the limbs. And, as I noted in my 2009 paper, the phylogenetic distribution of iliac chambers is consistent with pneumaticity, in that the chambers are only found in those sauropods that already have sacral pneumaticity (showing that pneumatic diverticula were already loose in their rear ends). But it’s nice to have confirmation.

So, the pneumatic ilia in Rocasaurus, Neuquensaurus, and Saltasaurus are cool because they suggest that all the other big chambers in sauropod ilia were pneumatic as well. And for those of you keeping score at home, that’s another parallel acquisition in Diplodocoidea and Somphospondyli (given the apparent absence of iliac chambers in Camarasaurus and the brachiosaurids, although maybe we should bust open a few brachiosaur ilia just to be sure*).

* I kid, I kid.**

** Seriously, though, if you “drop” one and find some chambers, call me!

Pectoral pneumaticity in saltasaurines. Cerda et al. (2012: fig. 2).

But that’s not all. The possibility of pneumatic ilia has been floating around for a while now, and most of us who were aware of the iliac chambers in sauropods probably assumed that eventually someone would find the specimens that would show that they were pneumatic. At least, that was my assumption, and as far as I know no-one ever floated an alternative hypothesis to explain the chambers. But I certainly did not expect pneumaticity in the shoulder girdle. And yet there they are: chambers with associated foramina in the scap and coracoid of Saltasaurus and in the coracoid of Neuquensaurus. Wacky. And extremely important, because this is the first evidence that sauropods had clavicular air sacs like those of theropods and pterosaurs. So either all three clades evolved a shedload of air sacs independently, or the basic layout of the avian respiratory system was already present in the ancestral ornithodiran. I know where I’d put my money.

There’s loads more interesting stuff to talk about, like the fact that the ultra-pneumatic saltasaurines are among the smallest sauropods, or the way that fossae and camerae are evolutionary antecedent to camellae in the vertebrae of sauropods, so maybe we should start looking for fossae and camerae in the girdle bones of other sauropods, or further macroevolutionary parallels in the evolution of pneumaticity in pterosaurs, sauropods, and theropods. Each one of those things could be a blog post or maybe a whole dissertation. But my mind is already thoroughly blown. I’m going to go lie down for a while. Congratulations to Cerda et al. on what is probably the most important paper ever written on sauropod pneumaticity.

References

  • Cerda, I.A., Salgado, L., and Powell, J.E. 2012. Extreme postcranial pneumaticity in sauropod dinosaurs from South America. Palaeontologische Zeitschrift. DOI 10.1007/s12542-012-0140-6
  • Janensch, W. 1947. Pneumatizitat bei Wirbeln von Sauropoden und anderen Saurischien. Palaeontographica, Supplement 7, 3:1–25.
  • Osborn, H. F. 1899. A skeleton of Diplodocus. Memoirs of the American Museum of Natural History 1:191–214.

Over at his truly unique blog Paleo Errata, Jeff Martz is claiming that Stereopairs Are Cool. This assertion he supports with the following figure that he put together, showing a set of five stereopairs of a Longosuchus braincase:

Unfortunately, I am one of those who can’t “see” stereopairs, so these images are uninformative to me — or, at least, no more informative than your average inch-wide braincase photo.

So how else can we envisage the stereo information in these pairs of photos that Jeff took?  My favourite way is using red-cyan anaglyphs — those goofy 3d images that you look at through 3d glasses.  To compare, I did this to Jeff’s image.  The process is simple: take two copies of the stereopair image, cut out all the right-eye views from one set and all the left-eye views from the other, then edit the colour levels of both layers.  In one, take the red right down to zero, so you only have blue+green=cyan; in the other take the green and blue down so you only have red.  Then stack one layer on top of the other and change its mode to “Lighten only”.  Export the result as a JPEG and you get this result:

Armed with my red-cyan glasses (which, remember, I got as a freebie with a Lego catalogue), I can now make out the 3d structure really easily.  Positives for the anaglyph approach:

  • The 3D image is much easier to see
  • The result takes up less space on the page
  • Most importantly, the size limitation is removed: I have some beautiful whole-screen anaglyphs (e.g. Archbishop cervical, wallaby skull), whereas stereograms are restricted to a couple of inches’ separation.

The downside is, of course, that you need special equipment to see them –albeit equipment so laughably minimal that Amazon.com will sell you THREE PAIRS for $1.39, you cheap gits.  But for those of who who are too poor to find $1.39, and who don’t have two friends with whom you can form an ad-hoc 3D-glasses buying consortium at a cost of $0.47 each, there is one further approach: a low-rent technique that I call a “wigglegram” for want of a better term.  Here it is:

I discovered this approach by accident, when flipping through a bunch of photographs that I’d taken of, I think, the Archbishop.  As a matter of policy, I take most of my photos twice, so that if I shake slightly or the auto exposure gets it wrong, I have a good copy that I can retain.  I was trying to decide which of two nearly identical pictures to keep.  But as it happened, I’d moved the camera slightly to the side between taking the first and the second, so as I skipped back and forth between them, I was seeing two slightly different perspectives.

So there you have it: three different ways to visualise 3d structure, each built from the same basic set of photos.  They each have their merits, and I hope we’ll increasingly see more of all three of them, as we move into the Shiny Digital Future, and arbitrary limits on manuscript length and numbers of figures get lifted.

I leave y0u with an actual application of all this.  Matt and I have, for some time, been working on a manuscript about caudal pneumaticity in sauropods, and we wanted to include a brief survey of which genera it’s been reported in.  Among the candidates was Saltasaurus, which has a candidate pneumatic caudal vertebra that was illustrated thus by Powell (2003: plate 53, part 3):

Matt can “see” stereograms, and insisted that the dark patch on the side of the centrum is a pneumatic fossa.  I wasn’t so sure, and in fact we got into quite an argument over whether or not to include this specimen in our list.  The argument was neatly concluded when I had the obvious idea of converting Powell’s stereogram into an anaglyph:

As soon as I saw this, I recognised what the structure is: the crescent moon-shaped dark patch is indeed a deep, invasive fossa, and the broad, roughly circular object above it and to the right is a lumpen lateral process sticking right out into the camera (and partially hiding the fossa).  So Matt was right, the vertebra is pneumatic, and a beautiful friendship was saved by the power of red-cyan anaglyphys.  Yay!

References

  • Powell, Jaime E.  2003.  Revision of South American Titanosaurid dinosaurs: palaeobiological, palaeobiogeographical and phylogenetic aspects.  Records of the Queen Victoria Museum 111: 1-94.

A section of the cotyle of a presacral vertebra of Alamosaurus (Woodward and Lehman 2009:fig. 6A).

The last time we talked about Alamosaurus, I promised to explain what the arrow in the above image is all about. The image above is a section through the cotyle (the bony socket of a ball-and-socket joint) at the end of one of the presacral vertebra. The external bone surface would have been over on the left; it was either very thin (which happens) or a bit eroded, or both. The arrow is pointing at something weird–a plate of bone inside the vertebra that forms a sort of shadow cotyle deep to the articular surface.

This is weird for a couple of reasons. First, once camellate (small-chambered) vertebrae get above a certain level of complexity, it’s hard to make any sense of the orientation of individual bony struts. Possibly I haven’t seen enough vertebrae, or played with enough 3D models, to figure it out. You would certainly expect that the struts would be oriented to resist biomechanical loads, just like the struts in the long bones of your limbs; the fact that sauropod verts were filled with air whereas your long bones are filled with marrow shouldn’t make any difference. Back in the day, Kent Sanders–who is second author on that super-important paper on unidirectional air flow in croc lungs that you’ve probably heard about (Farmer and Sanders 2010)–speculated to me that the complex of laminae we see in the vertebrae of most sauropods are still there in the inflated-looking vertebrae of titanosaurs and birds, they’re just incarnated in internal struts rather than external laminae. Cool hypothesis for somebody to test.

The other reason that this is weird is that the plate of bone is parallel to the articular surface. One place where I have seen some regularity in terms of strut orientation is in zygapophyses, where in both camerae and camellate vertebrae the internal struts are oriented at right angles to the articular surfaces of the zygs, like beams propping up a wall. In this Alamosaurus section, there are indeed smaller struts that run at right angles to both the cotyle and the internal plate, but I have no idea why they’re so wimpy and the plate is so thick; a priori I would have expected the reverse.

It turns out that this isn’t even the first time that an internal “shadow” of the cotyle has been figured–check out this figure that I redrew from Powell’s (1992:fig. 16) Saltasaurus osteology. But don’t credit me with the discovery. I’d looked at this section a hundred times and even drawn it and never noticed the shadow cotyle, until it was pointed out by Woodward and Lehman (2009)–another reason to read that paper if you haven’t yet. Kudos to Holly Woodward for spotting this and making the connection.

Now that I’ve drawn attention to the weirdness and given credit where it’s due, this is one of those times I’m going to throw up my hands in confusion and open the floor for comments.

References

  • Farmer, C.G., and Sanders, K. 2010. Unidirectional airflow in the lungs of alligators. Science 327:338-340.
  • Powell, J.E. 1992. Osteologia de Saltasaurus loricatus (Sauropoda – Titanosauridae) del Cretacico Superior del noroeste Argentino; pp. 165-230 in J.L. Sanz and A.D. Buscalioni (editors), Los Dinosaurios y Su Entorno Biotico: Actas del Segundo Curso de Paleontologia in Cuenca. Institutio Juan de Valdes.
  • Woodward, H.N.,  and Lehman, T.M. 2009. Bone histology and microanatomy of Alamosaurus sanjuanensis (Sauropoda: Titanosauria) from the Maastrichtian of Big Bend National Park, Texas. Journal of Vertebrate Paleontology 29(3):807-821.

ASPs for Alamosaurus

January 4, 2010

A section of the cotyle of a presacral vertebra of Alamosaurus (Woodward and Lehman 2009:fig. 6A). The arrow will be explained in a future post!

Last year was good for sauropod pneumaticity. In the past few months we’ve had the publication of the first FEA of pneumatic sauropod vertebrae by Schwarz-Wings et al (2009), as well as a substantial section on pneumaticity in the big Alamosaurus histology paper by Woodward and Lehman (2009). I won’t repeat here everything that Woodward and Lehman have to say about pneumaticity, I just want to draw attention to a little piece of it. Their work is observant, up-to-date, and worth reading, so if you can get access to the paper, read it.

The major brake on the growth of our knowledge and understanding of pneumaticity is sample size. I harped on this in 2005 (Wedel 2005), and Mike just brought it up again in a comment on a previous post. In fact, what he had to say is so relevant that I’m going to just cut and paste it here:

How does degree of pneumatisation vary between individuals? Here are three more: how does it vary along the neck, how does it vary long the length of an individual vertebra, and how does it vary through ontogeny? Then of course there is variation between taxa across the tree. So what we have here is a five-and-half-dimensional space that we want to fill with observations so that we can start to deduce conclusions. Trouble is, there are, so far, 22 published observations (neatly summarised by Wedel 2005:table 7.2), which is not really enough to let us map out 5.5-space! That’s one reason why, at the moment, each observation is valuable — it adds 4% to the total knowledge in the world.

To be fair, there are a few more published observations. Schwarz and Fritsch (2006) published ASPs for cervicals of Giraffatitan and Dicraeosaurus, and I have a gnawing feeling that there are a couple here and there that I’ve seen but not remembered. I’ve got some more of my own data in the as-yet-unpublished fourth chapter of my diss, which I failed to get out as part of the Paleo Paper Challenge. And, getting back to the subject of the post, Woodward and Lehman (2009:819) have some tasty new data to report:

Digital images of sections of vertebrae and ribs were imported into ArcGIS 8.1 (Dangermond, 2001; for methods see Woodward, 2005). A unitless value for the total area of the image was calculated, using the outline of the bone as a perimeter. Subtracted from this was the area value taken up by bone, as determined by color differences (lighter areas are camellate cavities, darker areas are bone). Using this method, longitudinal sections of centra are estimated to be roughly 65% air filled. The amount of open space similarly calculated for the pneumatic proximal and medial rib sections is about 52%, whereas the cancellous spongiosa in distal rib transverse sections yields an average estimate of about 44% of their cross sectional area. Hence, the camellate cavities result in an appreciably lower bone volume compared to spongiosa.

The ASP of 0.65 for centra is right in line with the numbers I’ve gotten for neosauropods, and with the results of Schwarz and Fritsch (2006) for Giraffatitan (Dicraosaurus had a much lower ASP, around 0.2 IIRC). The stuff about the ribs is particularly interesting. Using densities of 0.95 for bone marrow, 1.8 for avian (and sauropod) compact bone, and 1.9 for mammalian compact bone we get the following:

  • Pneumatic Alamosaurus vertebrae – ASP of 0.65, density of 0.63 g/cm^3.
  • Pneumatic Alamosaurus ribs – ASP of 0.52, density of 0.86 g/cm^3.
  • Apneumatic Alamosaurus ribs – MSP (marrow space proportion) of 0.44, density of 1.43 g/cm^3.
  • Pneumatic bird long bones – ASP of 0.59, density of 0.74 g/cm^3.
  • Apneumatic bird long bones – MSP of 0.42, density of 1.44 g/cm^3.
  • Apneumatic mammal long bones – MSP of 0.28, density of 1.63 g/cm^3.

ASPs and MSPs of bird and mammal bones are calculated from K values reported by Cubo and Casinos (2000) for birds and Currey and Alexander (1985) for mammals. I don’t know what the in vivo density of sauropod compact bone was; changing it from the avian value of 1.8 to the mammalian value of 1.9 would have a negligible effect on the outcome.

At least with the data in hand, we can make the following generalizations:

  • The apneumatic bones of birds are thinner-walled than those of mammals, on average. (This has been known for a long time.)
  • The apneumatic ribs of Alamosaurus were more similar in density to apneumatic bird bones than to apneumatic mammal bones.
  • In both birds and Alamosaurus, pneumatization reduces the amount of bone tissue present by 15-30% in the same elements (long bones for birds, ribs for Alamosaurus). Pneumatic bones are light not just because the marrow is replaced by air, but because there is less bone tissue than in apneumatic bones, as bird people have been observing for ages.

There’s loads more work to be done on this sort of thing, so I’m going to stop blogging now and get back to it. Stay tuned!

References