As I mentioned a few days ago, Matt and I have a couple of papers in the new PLOS ONE Sauropod Gigantism collection. We were each lead author on one and second author on the other, so for convenience’s sake we’ll refer to them as my paper (Taylor and Wedel 2013c on neck cartilage) and Matt’s paper (Wedel and Taylor 2013b on caudal pneumaticity.)

Mine is very simple in concept (although it ended up at 17 pages and 23 figures). It’s all about addressing one of the overlooked variables in reconstructing the postures of the necks of sauropods (and indeed of all tetrapods). That is, the spacing between consecutive vertebrae, and the effect this has on “neutral pose”.

The concept of “neutral pose” goes back to the DinoMorph work of Stevens and Parrish (1999). They defined it (p. 799) as follows: “We determined the neutral poses for each animal, wherein the paired articular facets of the postzygapophyses of each cervical vertebra were centered over the facets of the prezygapophyses of its caudally adjacent counterpart.”

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Taylor and Wedel (2013c: Figure 3). Articulated sauropod vertebrae. Representative mid-cervical vertebra of Giraffatitan brancai, articulating with its neighbours. The condyle (ball) on the front of each vertebra’s centrum fits into the cotyle (socket) at the back of the preceding one, and the prezygapophyses articulate with the preceding vertebra’s postzygapophyses. These vertebrae are in Osteological Neutral Pose, because the pre- and postzygapophyseal facets overlap fully.

One of the more fundamental flaws in Stevens and Parrish (1999) is the assumption that animals habitually rest their necks in neutral pose — an assumption that is unsupported by evidence and, as it turns out, false (Vidal et al. 1986, Taylor et al. 2009). But let’s leave that aside for the moment, and consider what neutral pose actually represents.

The fact that there is even such a thing as neutral articulation between two consecutive vertebrae is due to there being three points of contact between those vertebra: as with the legs of a tripod, three points is the minimum number you need to fix an object in three-dimensional space. Two of these points are at the zygapophyses, as noted in the original definition above. The third point is the articulation between the centra.

The centrum has been curiously overlooked in discussions of neutral pose, but needless to say its length is crucial in establishing what is neutral. In the image above, if the centrum was longer, then the angle between the consecutive vertebrae would need to be raised in order to keep the zygapophyses articulated.

And of course it was longer in life, because of the cartilage in between the consecutive centra. (The use of the more specific term “osteological neutral pose” goes some way to recognising that tissues other than bone have been overlooked, but the problem has not really been addressed or even properly acknowledged in published works before our paper.)

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Taylor and Wedel (2013c: Figure 5). Intervertebral gaps in camel necks. Head and neck of dromedary camels. Top: UMZC H.14191, in right lateral view, posed well below habitual posture, with apparently disarticulated C3/C4 and C4/C5 joints. Photograph taken of a public exhibit at University Museum of Zoology, Cambridge, UK. Bottom: OUMNH 17427, in left lateral view, reversed for consistency with Cambridge specimen. Photograph taken of a public exhibit at Oxford University Museum of Natural History, UK. Inset: detail of C4 of the Oxford specimen, showing articulations with C3 and C5. The centra are separated by thick pads of artificial ‘‘cartilage’’ to preserve spacing as in life.

You simply can’t ignore cartilage when modelling neck postures and expect to get anything resembling a meaningful result. That is, presumably, the reason why the habitual posture of rabbits in life exceeds the most extended posture we were able to obtain when manipulating dry vertebrae of a hare: compare Vidal et al. (1986: fig. 4) with Taylor et al. (2009: fig. 1).

How big is the effect? That depends on the thickness of the cartilage and the height of the zygapophyses above the center of rotation. Here is an illustration that we should have put in the paper, but which inexplicably neither of us thought of:

figNEW-angle-at-zygs

Influence of intervertebral cartilage on vertebral articulation angle. Consider the posterior vertebra (black) as fixed. The blue vertebra represents neutral pose of the preceding vertebra with centra abutting and zygapophyseal facets maximally overlapped. The red vertebra indicates neutral pose once intervertebral cartilage is added between the vertebra (where else?) The green lines show the angle by which the more anterior vertebra must be inclined in order to accommodate the cartilage, and the magenta line shows the height of the zygapophyseal articulation above the center of rotation between the two vertebrae.

Here’s some elementary trigonometry. Suppose the intervertebral cartilage is x distance thick at mid-height of the centra, and that the height of the zygs above this mid-height point (the magenta line) is y. The triangle between the middle of the condyle of the posterior vertebra, the middle of the cotyle of the anterior one and the zygapophyseal articulation is near enough a right-angled triangle as makes no odds.

Consider the angle θ between the green lines. Sin(θ) = opposite/hypotenuse = x/y, and by similarity, the additional angle of inclination of the anterior vertebra is also θ.

But for small angles (and this is generally a small angle), sin(θ) ≈ θ. So the additional inclination in radians = cartilage thickness divided by zygapophyseal height. For example, in vertebrae where the zygs are 23 cm above the mid-height of the centra, adding 4 cm of intervertebral cartilage adds about 4/23 = 0.174 radians = 10 degrees of extra inclination. (That’s pretty similar to the angle in the illustration above. Eyeballing the cartilage thickness and zyg height in the illustration suggests that 23:4 ratio is about right, which is a nice sanity-check of this method.)

millionaire-stupid-contestant4

At this point, I am cursing my own stupidity for not putting this diagram, and the very simple calculation, into the paper. I guess that can happen when something is written in a hurry (which to be honest this paper was). The formula is so simple — and accurate enough within tolerances of inevitable measurement error — that we really should have used it all over the place. I guess that will have to go in a followup now. [Update, 5th November 2014. It’s long overdue, but that followup paper has finally been submitted and is available as a preprint.]

Anyway — next time, we’ll address this important related question: how thick, in fact, was the cartilage between the cervicals of sauropods?

References

Because I am preparing this paper from PLOS ONE, with its stupid numbered-references system, I am finally getting to grips with a reference-management system. Specifically, Zotero, which is both free and open source, which means it can’t be taken over by Elsevier.

As a complete Zotero n00b, I’ve run into a few issues that more experienced users will no doubt find laughable. Here are two of them. I need to cite Greg Paul’s classic 1988 paper on the skeletal reconstruction of Giraffatitan:

Paul, Gregory S. 1988. The brachiosaur giants of the Morrison and Tendaguru with a description of a new subgenus, Giraffatitan, and a comparison of the world’s largest dinosaurs. Hunteria 2(3):1-14.

When I render this using Zotero’s PLOS ONE style, it comes out as:

Paul GS (1988) The brachiosaur giants of the Morrison and Tendaguru with a description of a new subgenus, Giraffatitan, and a comparison of the world’s largest dinosaurs. Hunteria 2: 1–14.

So the first problem is, how can I get Giraffatitan to be set in italics?

And the second one, which is arguably more important, is how can I get the issue number included? I undertsand that PLOS ONE referencing style omits the issue-numbers by preference, since they are often redundant, with the pages of each volume being numbered consecutively across volumes. But Hunteria is one of those journals (PaleoBios is another) that resets page-numbers at the start of each issue. As a result, Hunteria volume 2 had at least three page 14s, one in each of its issues, so that issue number is a crucial part of the reference.

Help me, SV-POW! readers — you’re my only hope.

Given the huge amount we’ve written about open access on this blog, it may come as a surprise to realise that the blog itself has not been open access until today.  It’s been free to read, of course, but in the absence of an explicit licence statement, the default “all rights reserved” has applied, which has meant that technically you’re not supposed to do things like, for example, using SV-POW! material in course notes.

It was never our intention to be so restrictive, of course.  We always wanted what we write to be as widely useful as possible; but like most bloggers, we just didn’t think about what that entailed.

So now, belatedly, we are placing SV-POW! under the Creative Commons Attribution licence.  This means that you can do anything with our content, subject only to giving us credit.  Go nuts.  We want our work to be useful.  (Our use of this licence is indicated by the CC BY button at top right of all the pages.)

Note that SV-POW! is now compliant with the Budapest Open Access Initiative’s definition of open access — the only definition that matters, really, since it’s where the term “open access” was first coined.  That definition is rather noble and striking:

By ‘open access’ to this literature, we mean its free availability on the public internet, permitting any users to read, download, copy, distribute, print, search, or link to the full texts of these articles, crawl them for indexing, pass them as data to software, or use them for any other lawful purpose, without financial, legal, or technical barriers other than those inseparable from gaining access to the internet itself. The only constraint on reproduction and distribution, and the only role for copyright in this domain, should be to give authors control over the integrity of their work and the right to be properly acknowledged and cited.”

We are applying this licence restrospectively to all the original content on the site — not just what we write from now on.  To ensure that we’re on safe ground doing this, all three of us agreed on this measure, and we also obtained consent from the only (so far) guest-blogger on SV-POW!, Heinrich Mallison.

Finally, we should note the exceptions to the CC BY licence. When we’ve included material from other sources — most often figures from published papers — we do not own the copyright and can’t licence it.  Similarly, all photographs of fossils held by the Natural History Museum in London are copyright the museum.  If you want to re-use any of the non-original material, you’ll need to track down the copyright holders and negotiate with them.

This year, I missed The Paleo Paper Challenge over on Archosaur Musings — it was one of hundreds of blog posts I missed while I was in Cancun with my day-job and then in Bonn for the 2nd International Workshop on Sauropod Biology and Gigantism.  That means I missed out on my annual tradition of promising to get the looong-overdue Archbishop description done by the end of the year.

Brachiosauridae incertae sedis NMH R5937, "The Archbishop", dorsal neural spine C, probably from an anterior dorsal vertebra. Top row: dorsal view, anterior to top; middle row, left to right: anterior, left lateral, posterior, right lateral; bottom row: ventral view, anterior to bottom.

But this year, Matt and I are going to have our own private Palaeo Paper Challenge.  And to make sure we heap on maximum pressure to get the work done, we’re announcing it here.

Here’s the deal.  We have two manuscripts — one of them Taylor and Wedel, the other Wedel and Taylor — which have been sitting in limbo for a stupidly long time.  Both are complete, and have in fact been submitted once and gone through review.  We just need to get them sorted out, turned around, and resubmitted.

(The Taylor and Wedel one is on the anatomy of sauropod cervicals and the evolution of their long necks.  It’s based on the last remaining unpublished chapter of my dissertation, and turned up in a modified form as my SVPCA 2010 talk, Why Giraffes Have Such Short Necks.  The Wedel and Taylor one is on the occurrence and implications of intermittent pneumaticity in the tails of sauropods, and turned up as his SVPCA 2010 talk, Caudal pneumaticity and pneumatic hiatuses in the sauropod dinosaurs Giraffatitan and Apatosaurus.)

We’re going to be realistic: we both have far too much going in (incuding, you know, families) to get these done by the end of 2011.  But we have relatively clear Januaries, so our commitment is that we will submit by the end of January 2012.  If either of us fails, you all have permission to be ruthlessly derisive of that person.

… and in other news …

Some time while we were all in Bonn, the SV-POW! hit-counter rolled over the One Million mark.  Thanks to all of your for reading!

 

Back when Darren and I did the Xenoposeidon description, we were young and foolish, and only illustrated the holotype vertebra NHM R2095 in four aspects: left and right lateral, anterior and posterior.  No dorsal or ventral views.

Also, because the figure was intended for Palaeontology, which prints only in greyscale, I stupidly prepared the figure in greyscale, rather than preparing it in colour and then flattening it down at the last moment.  (Happily I’d learned that lesson by the time we did our neck-posture paper: although it was destined for Acta Palaeontologia Polonica, which also prints in greyscale, and though the PDF uses greyscale figures, the online full-resolution figures are in colour.)

As if that wasn’t dumb enough, I also composited the four featured views such that the two lateral views were adjacent, and above the anterior and posterior views — so it wasn’t easy to match up features on the sides and front/back between the views.  Since then, I have landed on a better way of presenting multi-view figures, as in my much-admire’d turkey cervical and pig skull images.

So, putting it all together, here is how we should have illustrated illustrated Xenoposeidon back in 2007 (click through for high resolution):

(Top row: dorsal view, with anterior facing left; middle row, from left to right: anterior, left lateral, posterior, right lateral; bottom row, ventral view, with anterior facing left.  As always with images of NHM-owned material, this is copyright the NHM.)

Of course, if we’d published in PLoS ONE, then this high-resolution (4775 x 4095), full colour image could have been the published one rather than an afterthought on a blog somewhere.  But we didn’t: back then, we weren’t so aware of the opportunities available to us now that we live in the Shiny Digital Future.

In other news, the boys and I all registered Xbox Live accounts a few days ago.  I chose the name “Xenoposeidon”, only to find to my amazement that someone else had already registered it.  But “Brontomerus” was free, so I used that instead.

People who’ve been paying especially close attention may have noted than on four separate occasions in the last eighteen months, I’ve casually referred to our old buddy HMN SII as the paralectotype specimen of Giraffatitan brancai.  (Butchering a wallaby, photographing big bones, How fat was Camarasaurus, and baby giraffe neck, in case you were wondering.)

Giraffatitan brancai paralectotype HMN SII in the justly underrated left posteroventrolateral view, slightly obscured by a bit of Boring Old Diplodocus neck

But in my Big Brachiosaur Bonanza (Taylor 2009:788), I nominated HMN SII as the lectotype of this species.  So why all this paralectotype stuff?  Well, what I wrote in the paper was:

The original type specimen, “Skelett S” (Janensch, 1914:86) was subsequently found (e.g., Janensch, 1929:8) to consist of two individuals, which were designated SI (the smaller) and SII (the larger and more complete). Janensch never explicitly designated these two specimens as a syntype series or nominated either specimen as a lectotype; I therefore propose HMN SII as the lectotype specimen of Brachiosaurus brancai.

But in May last year, I got an email from Mark Konings, a dinosaur enthusiast from the Netherlands, pointing out (more politely than I deserved) that I’d got this wrong.  In fact, Janensch did nominate a lectotype — the wrong one, SI, but we’re stuck with it.  He did this in a paper on skulls (Janensch 1935-1936:151), which is why I overlooked it.  (Well, that and the fact that he rather inconsiderately wrote in German.)

Once I’d been shown my mistake, I realised that the only thing to do was formally correct it in JVP, where the original article had been, so I sent them the shortest and most boring manuscript I’ve ever written (and it is up against some pretty stiff competition in the “most boring” category).  And that manuscript was published today (Taylor 2011), fixing my dumb mistake.

Many thanks to Mark for spotting this!

References

This tutorial is based on all the things that I stupidly forgot to do along the way of tearing down the juvenile giraffe neck that Darren, John Conway and I recently got to take to pieces.  At half a dozen different points in that process, I found myself thinking “Oh, we should have done X earlier on!”  So it’s not a tutorial founded on the idea that I know how this should be done; it’s about how I am only now realising how it should be done, off the back of my dumb mistakes.

Cervical vertebra 5 of two-week-old giraffe: left column, anterior; middle column, top to bottom, dorsal, left lateral, posterior, all with anterior to the left; right column, posterior

What you want is to get the maximum possible information out of your specimen.  At each stage of preparation, information is lost — a necessary evil, because of course at the same time new information becomes available.  So don’t miss anything early on.

The whole neck

If you’re lucky, you’ll get the complete, intact neck to work with.  (Ours was not quite intact, having been skinned, and lost an indeteminate amount of superficial muscle and ligament in the process.)  So before you start cutting, photograph the neck in dorsal, ventral, lateral, anterior and posterior aspects.

Next, you want to measure the neck:

  • total mass
  • total length, front of atlas to back of last centrum.
  • maximum flexion (i.e. downwards bend)
  • maximum extension (i.e. upwards bend)
  • maximum deflection (i.e. lateral bend)

These last three are hard to do, because “maximum” flexion, extension and deflection are not exact things.  You can always push or squeeze or bend a bit harder.  These are the unpleasantly messy aspects of working with animals rather than robots — most kinds of tissue are flexible and resilient.  You just have to do the best you can, and supplement your measurements with photographs of the neck bent in each direction.

Skinning

Now you’re ready to start taking that baby apart.  Get the skin off, then redo all your photos and redo all your measurements — yes, even total length, even though you “know” removing the skin can’t affect that.  Because you don’t know what you don’t know.  Does removing the skin affect the maximum range of movement?  How much of the neck’s total mass was due to the skin?  Weigh the skin as well: does its mass added to that of the deskinned neck add up to that of the intact neck?  If not, is the discrepancy due to blood loss?

Stripping muscle

Once the skin is off, you can start removing muscles.  Ideally, you want to identify each muscle as you go, and remove them one by one, so that you leave the major ligaments behind.  In practice this is harder than it sounds, because the muscles in real necks are, inconveniently, not clearly delineated and labelled like the ones in books.  Still, going slowly and carefully, it’s often possible to avoid cutting actual muscles but just the fascia between them, which allows you remove complete muscles.  Done well, this can leave in place not only the nuchal ligament running along the top of all the neural spines, but the shorter ventral ligaments joining adjacent vertebrae.

John (left) and Darren (right) removing muscle from the giraffe neck (in right lateral aspect), while keeping ligaments intact

As you’re doing this, you want to avoid damaging the intercentral joints and the zygapophyseal capsules, so far as possible.  You’ll probably find it easy to preserve the former, which are tough, but harder not to accidentally damage at least some of the latter.  You want to keep them intact as far as possible, so you can see how the react when you manipulate the neck.  (Do these manipulations gently, or you’ll tear those capsules.)

Now that the skin and muscles are both off — at least, so far as you can remove the muscles, which will not be completely — you can redo all your photos and redo all your measurements again.  Yes, all of them.  Because you just can’t tell what you’re going to be interested in later, and curse yourself for missing.

Stripping ligament

Go right ahead.  Remove the short ligaments, and do your best to get the nuchal ligament off all in one chunk — not quite as easy as it sounds, because it doesn’t just sit on top of the neural spines, but sort of encloses them.  Measure the nuchal ligament at rest, then stretch it out as far as you can and measure it extended.  Calculate how far it stretched as a proportion of the rest length.  Compare this with what you learned from Alexander (1989:64-65).  Hmm.  Interesting, no?

You can guess what’s coming now: redo all your photos and redo all your measurements yet again.  You should find that the total length is the same, but who knows what you might find about changing flexibility?  Also, your progressive sequence of mass measurements will tell you what proportion of the whole neck was skin, muscle, ligament, etc.

Separating the vertebrae

This sounds like it should be easy, but it’s not.  The zygapophyses will come apart very easily, but the centra will be held firmly together with very dense connective tissue which has be cut carefully away, piece by piece, with the blade of a scalpel worked between the condyle of one vertebra and the cotyle of the next.  (I’m writing here about a giraffe neck, but I’m confident the same will be true of other artiodactyls and maybe most mammals; bird necks are different.)

Once you’ve got the vertebrae separate, photograph each vertebra separately, from each of the cardinal directions. Also, measure each vertebra separately — especially for centrum length, but you may as well get all the major measurements.  These measurements will include the cartilage caps at the front and back of each centrum.  (This is the step that I most regret missing out.)

Articulate the vertebrae in “neutral pose” by keeping the centra in full contact and rotating each intercentral joint about its midpoint until the corresponding zygapophyses are maximally overlapped.  What does this pose look like?  How does it compare to the animal’s habitual pose in life?  (If possible, compare with the pose shown by an X-ray of the live animal, since necks lie.)

Articulate the vertebrae in positions of “maximal” flexion, extension and deflection by keeping the centra in full contact and rotating each intercentral joint about its midpoint until the corresponding zygapophyses are displaced to a degree of your choosing.  Try it with the zygs allowed to slide until they are 50% disarticulated, then with 75% disarticulation, then displacing until they are just past the point of contacting each other.  Photograph all these poses and measure their deflection.  Compare these variant poses with those obtained when the vertebrae were still joined together, and when the ligaments, muscles and skin were still in place.  What degree of zygapophyseal disarticulation best matches the whole-neck bending ability?  How does this vary along the neck?  How does that this compare with what you may have been led to expect in the literature.  Hmm.

Using your earlier photos of the whole neck’s bending profile, arrange the vertebrae in the exact same pose.  How much do the zygapophyses disarticulate in these poses?  As you rotate the joints about the articulation of their centra, do the zygs just slide neatly past each other, or do they move far apart from each other as the neck bends?  Interesting, yes?

Cleaning the vertebrae

Have you recorded all the information you need from the intact vertebrae with their cartilage in place?  If you’re sure, then …

Lightly simmer the vertebrae for an hour or so, then remove the excess flesh by hand and using a toothbrush.  Repeat as needed to get them clean.  If you can do this really carefully — I couldn’t — you may be able to keep the cartilage firm, and firmly articulated with the bone.  (Bugging the vertebrae is probably a better approach for this purpose, but I find it hard to be that patient.)

Once the vertebrae have dried out — and especially, once their cartilage is dry — re-measure each vertebra.  Does the drying of the cartilage affect the centrum length?

Simmer the vertebrae again and gently peel off the cartilage caps at the front and back of each centrum.  Re-measure the centra: how long are they now?  What proportion of each centrum’s length was cartilage?

Articulate all the centra in a straight line, and measure the total length.  How does this compare with the whole-neck length you started with?  [Crib-sheet answer for our baby giraffe: 41 cm vs. a whole-neck length of 51 cm.  Expect a closer match if you’re dealing with an adult animal,which will have proportionally less cartilage.]

Articulate the vertebrae in “neutral pose” as you did back when the individual vertebrae were complete.  How does the new “neutral pose” compare with the old one?  With habitual life posture?  Huh.  Makes you think, doesn’t it?

Nearly done …

Articulate the vertebrae in positions of “maximal” flexion, extension and deflection as you did before, and compare your results with those from when the vertebrae were complete with their cartilage caps.  Well!  Who’d have thought?

Now remember that the fossils we have of, say, sauropod cervicals are those of the dry bone only, with no cartilage.  Think about how different the “neutral pose” and range of movement would be if we had the intact vertebrae with their cartilage.

Dammit all, I’ve given the game away

As I wrote this article, I found myself giving away more and more of a paper I’ve been planning to write, in which I go through essentially this process with a couple of necks, ideally from very different clades, and write up the results.  Say, a giraffe, an ostrich and  a croc.  The extent to which the dry-bone postures and flexibility vary from those of the live animals would give us a reasonable starting point for thinking about how life postures and flexibility of sauropods might have varied from what we’d deduce from the dry bones alone.

Wouldn’t that be a great little paper?

Well, I might still write it when I find the time, but I won’t stand in the way of anyone else who wants to plough straight in and just get it done.  (You might mention me in the acknowledgements if you do.)


I’m stupid

February 20, 2011

Earlier this evening, while I was editing an SV-POW! article that we plan to release on Wednesday, I (Mike) inadvertently hit the Publish button rather than Save Draft as I’d intended.  I was able to quickly undo the posting, but it’s possible that some of you may have seen Wednesday’s article prematurely, especially if you use an RSS reader that happened to cache that page during the brief period that it was available.

I am asking you all, please, to limit the damage from my stupidity by not discussing that article or its subject at all until Wednesday.  Please don’t even say what it was about.

Thanks for understanding.

How fat was Camarasaurus?

January 16, 2011

For reasons that will soon become apparent (yes, that’s a teaser), Matt and I wanted to figure out how heavy Camarasaurus was.  This is the story of how I almost completely badgered up part of that problem.  I am publishing it as a cautionary tale because I am very secure and don’t mind everyone knowing that I’m an idiot.

Those who paid close attention to my recent paper on Brachiosaurus and Giraffatitan will remember that when I estimated their mass using Graphic Double Integration (Taylor 2009: 802-804) I listed separately the volumes of the head, neck, forelimbs, hindlimbs, torso and tail of each taxon.  In Giraffatitan, the torso accounted for 71% of the total volume (20588 of 29171 litres), and in Brachiosaurus, 74% (26469 of 35860 litres), so it’s apparent that torso volume hugely dominates that of the whole animal.  In the giant balloon-model Giraffatitan of Gunga et al.’s (1995, 1999) estimates, the torso accounted for 74% of volume (55120 of 74420 litres) so even though their fleshing out of the skeleton was morbidly obese, the relative importance of the torso came out roughly the same.  Finally, Gunga et al’.s (2008) revised, less bloated, model of the same Giraffatitan had the torso contributing 68% of volume (32400 of 47600 litres).  So far as I know, these are all of the published accounts that give the volumes of separate parts of a sauropod body, but if there are any more, please tell me in the comments!   (Odd that they should all be for brachiosaurids.)

3D “slim” version of reconstruction of the “Brachiosaurus” brancai mounted and exhibited at the Museum of Natural History in Berlin (Germany).  A. Side view, upper panel; B. top view, lower panel.  The cross in the figure of upper panel indicates the calculated center of gravity.  (Gunga et al. 2008: figure 2)

So it’s evident that, in brachiosaurs at least, the torso accounts for about 70% total body volume, and therefore for about that much of the total mass.  (The distribution of penumaticity means that it’s denser than the neck and less dense than the limbs, so that its density is probably reasonably close to the average of the whole animal.)

Now here’s the problem.  How fat is the sauropod?  Look at the top-view of Giraffatitan in the Gunga et al. figure above: it’s easy to imagine that the torso could be say 20% narrower from side to side, or 20% broader.  Those changes to breadth would affect volume in direct proportion, which would mean (if the torso is 70% of the whole animal) a change in total body volume of 14% either way.  Significant stuff.

So what do we know about the torso breadth in sauropods?  It obviously dependant primarily on the orientation of the ribs and their articulation to the dorsal vertebrae.  And what do we know about that?

Nothing.

Well, OK, I am over-simplifying a little.  It’s been mentioned in passing in a few papers, but it’s never been discussed in any detail in a published paper that I know of.  (There’s a Masters thesis out there that starts to grapple with the subject, but I don’t know whether I should talk about that while it’s still being prepared for publication, so I won’t say anything more.)  The most important published contribution is more than a century old — Holland’s (1910) smackdown of Tornier’s and Hay’s comical Diplodocus postures, which included the following cross-sections of the torsos of several animals at the seventh dorsal vertebra:

(This figure previously appeared on SV-POW! in Matt’s post, Sauropods were tacos, not corn dogs, which as far as I am aware is the only existing non-technical treatment of sauropod torso-shape.)

Holland unfortunately did not discuss the torso shape that he illustrated, merely asserting it.  Presumably it is based on the mounted skeleton of the Diplodocus carnegii holotype CM 84, which is at the Carnegie Museum in Pittsburgh, where Holland was based.  I have no reason to doubt it; just noting that it wasn’t discussed.

All right then — what about Camarasaurus?  I think it’s fair to say that it’s generally considered to be fairly rotund among sauropods, as for example this skeletal reconstruction by Greg Paul shows:

Camarasaurus lentus skeletal reconstruction, in dorsal and right lateral views. (Paul 2010:197)

Measuring off the height and width of the torso at the seventh dorsal vertebra, using GIMP, I find that they are 341 and 292 pixels respectively, so that the eccentricity is 341/292 = 1.17.  This compares with 1760/916 = 1.92 for Holland’s Diplodocus above, so if both figures are accurate, then Camarasaurus is much fatter than Diplodocus.

But is Paul’s Camarasaurus ribcage right?  To answer that, I went back to my all-time favourite sauropod paper, Osborn and Mook’s (1921) epic descriptive monograph of Camarasaurus (and Cope’s other sauropods).  I knew that this awesomely comprehensive piece of work would include plates illustrating the ribs; and in fact there are four plates that each illustrate a complete set of dorsal ribs (although the associations are doubtful).  Here they all are:

Left dorsal ribs of Camarasaurus (Osborn and Mook 1921:pl. LXXVIII)

Left dorsal ribs of Camarasaurus (Osborn and Mook 1921:pl. LXXIX)

Left dorsal ribs of Camarasaurus (Osborn and Mook 1921:pl. LXXX)

Left dorsal ribs of Camarasaurus (Osborn and Mook 1921:pl. LXXXI)

But hang on a minute — what do you get if you articulate these ribs with the dorsal vertebrae?  Osborn and Mook also provided four plates of sequences of dorsal vertebrae, and the best D7 of the four they illustrate is probably the one from plate  LXX.  And of the four 7th ribs illustrated above, the best preserved is from plate LXXIX.  So I GIMPed them together, rotated the ribs to fit as best I could and …

What on earth?!

I spent a bit of time last night feeling everything from revulsion to excitement about this bizarre vertebra-and-rib combination.  Until I happened to look again Osborn and Mook — earlier on, in the body of the paper, in the section about the ribs.  And here’s what I saw:

(Note that this is the vertebra and ribs at D4, not D7; but that’s close enough that there’s no way there could be a transition across three vertebrae like the change between this and the horrible sight that I presented above.)

What’s going on here?  In the plates above, the ribs do not curve inwards as in this cross-section: they are mostly straight, and in many case seem to curve negatively — away from the torso.  So why do O&M draw the ribs in this position that looks perfectly reasonable?

And figure 70, a few pages earlier, makes things even weirder: it clearly shows a pair of ribs curving medially, as you’d expect them to:

So why do these ribs look so totally different from those in the plates above?

I’ll give you a moment to think about that before I tell you the answer.

Seriously, think about it for yourself.  While you’re turning it over in your mind, here is a picture of the beautiful Lego kit #10198, the Blockade Runner from the original Star Wars movie.  (I deeply admire the photography here: clear as a bell.)

OK, welcome back.

Got it?  I bet most of you have.

The answer was right there in figure 71:

Osborn and Mook 1921:fig. 71. Left rib of Camarasaurus supremus Cope. Rib 4 (Amer. Mus. Cope Coll. No. 5761/R-A-24). (A) direct external view when placed as in position in the body; (B) direct anterior when placed as in position in the body. Capit. capitulum; Sh. shaft; Tub. tuberculum. Reconstructed view, portion in outline.

Osborn and Mook 1921:fig. 71. Left rib of Camarasaurus supremus Cope. Rib 4 (Amer. Mus. Cope Coll. No. 5761/R-A-24). (A) direct external view when placed as in position in the body; (B) direct anterior when placed as in position in the body. Capit. capitulum; Sh. shaft; Tub. tuberculum. Reconstructed view, portion in outline.

And, my word, isn’t it embarrassingly obvious once you see it?  I’d been blithely assuming that the ribs in O&M’s plates were illustrated in anterior view, with the capitula (which articulate with the parapophyses) located more medially, as well as more ventrally, than the tubercula (which articulate with the diapophyses).  But no: as in fact the captions of the plates state perfectly clearly — if I’d only had the wits to read them — the ribs are shown in “external” (i.e. lateral) view.  Although it’s true that the capitula in life would indeed have been more medially positioned than the tubercula, it’s also true that they were more anteriorly positioned, and that’s what the plates show at the rib heads.  And the curvature that I’d been stupidly interpreting as outward, away from the midline, is in fact posteriorly directed: the ribs are “swept back”.  The ventral portions of the ribs also curve medially, away from the viewer and into the page … but of course you can’t see that in the plates.

The important truth — and if you take away nothing else from this post, take this — is that I am dumb bones are complex three-dimensional objects, and it’s impossible to fully understand their shape from single-view illustrations.  It’s for this reason that I make an effort, when I can, to illustrate complex bones from all cardinal directions — in particular, with the Archbishop bones, as for example “Cervical S” in the Brachiosaurus coracoid post.

Because ribs, in particular, are such complex shapes — because their curvature is so unpredictable, and because their articulation with the dorsal vertebrae is via two points which are located differently on successive vertebrae, and because this articulation still allows a degree of freedom of movement — orthogonal views, even from all cardinal directions, are of limited value.  Compositing figures will give misleading results … as demonstrated above.  PhotoShop is no more use here.  Fly, you fools!

Paradoxically, our best source of information on the shapes of saurpod torsos is: mounted skeletons.  I say “paradoxically” because we’ve all grown used to the idea that mounts are not much use to us as scientists, and are really there only as objects of awe.  As Brian Curtice once said, “A mounted skeleton is not science.  It’s art.  Its purpose is to entertain the public, not to be a scientifically accurate specimen”.  In many respects, that’s true — especially in skeletons like that of the “Brontosaurus” holotype, YPM 1980, where the bones are restored with, and in some cases encased in, plaster so you can’t tell what’s what.  But until digital scanning and modelling make some big steps forward, actual mounted skeletons are the best reference we have for the complex articulations of ribs.

Giraffatitan brancai paralectotype HMN SII, composite mounted skeleton, torso in left posteroventrolateral view (photograph by Mike Taylor)

And I finish this very long (sorry!) post with yet another note of caution.  Ribs are long and thin and very prone to damage and distortion.  It’s rare to find complete sauropod ribs (look closely at the O&M plates above for evidence), but even when we do, we shouldn’t be quick to assume that the shape in which they are preserved is necessarily the same as the shape they had in life.  (If you doubt this, take another look at rib #6 in the third of the four O&M plates above.)  And as if that weren’t enough to discourage us, we should also remember that the vertebra-rib joints would have involved a lot of cartilage, and we don’t know its extent or shape.

So bearing in mind the complicated 3D shape of ribs and of dorsal vertebrae, the tendency for both to distort during and after fossilisation, and the complex and imperfectly known nature of the joints between them, I think that maybe I wasn’t too far wrong earlier when I said that what we know about sauropod torso shape is: nothing.

It’s a sobering thought.

References

I do not dare behold it

January 14, 2011

By a curious coincidence, today’s Bob The Angry Flower cartoon is all about the Archbishop description.

Enjoy.

But, hey, at least I got my confession in early — I was officially the first participant to fail the 2010 Paleo Project Challenge.

THIS year, for sure!