We jumped the gun a bit in asking How fat was Camarasaurus? a couple of years ago, or indeed How fat was Brontosaurus? last year. As always, we should have started with extant taxa, to get a sense of how to relate bones to live animals — as we did with neck posture.

So here we go. I give you a herd of Indian elephants, Elephas maximus (from here):

056-Elephant-c-Gehan-de-Silva-Wijeyeratne-Minneriya-2004-07-27-165-Gathering

You will notice, from this conveniently-close-to-anterior view, that their torsos bulge out sideways, much further than the limbs.

Now let’s take a look at the skeleton of the same animal in the Oxford University Museum of Natural History (downloaded from here but for some reason the photo has now gone away):

4795746797_575d1f0ce6_b

The rib-cage is tiny. It doesn’t even extend as far laterally as the position of the limb bones.

(And lest you think this is an oddity, do go and look at any mounted elephant skeleton of your choice, Indian or African. They’re all like this.)

What’s going on here?

Is Oxford’s elephant skeleton mounted incorrectly? More to the point, are all museums mounting their elephants incorrectly? Do elephants’ ribs project much more laterally in life?

Do elephants have a lot of body mass superficial to the rib-cage? If so, what is that mass? It’s hard to imagine they need a huge amount of muscle mass there, and it can’t be guts. Photos like this one, from the RVC’s televised elephant dissection on Inside Nature’s Giants, suggest the ribs are very close to the body surface:

01020162576700

I’m really not sure how to account for the discrepancy.

Were sauropods similarly much fatter than their mounted skeletons suggest? Either because we’re mounting their skeletons wrongly with the ribs too vertical, or because they had a lot of superficial body mass?

Consider this mounted Camarasaurus skeleton in the Dinosaur Hall at the Arizona Museum of Natural History (photo by N. Neenan Photography, CC-BY-SA):

Camarasaurus_skeleton

Compare the breadth of its ribcage with that of the elephant above, and then think about how much body bulk should be added.

This should encourage palaeoartists involved in the All Yesterdays movement to dramatically bulk up at least some of their sauropod restorations.

It should also make us think twice about our mass estimates.

I’ve recently written about my increasing disillusionment with the traditional pre-publication peer-review process [post 1, post 2, post 3]. By coincidence, it was in between writing the second and third in that series of posts that I had another negative peer-review experience — this time from the other side of the fence — which has left me even more ambivalent about the way we do things.

On 17 July I was asked to review a paper for Biology Letters. Having established that it was to be published as open access, I agreed, was sent the manuscript, and two days later sent a response that recommended acceptance after only minor revision. Eleven days later, I was sent a copy of the editor’s decision — a message that included all three reviewers’ comments. I can summarise those reviewers’ comments by directly quoting as follows:

Revewer 1: “It is good to have this data published with good histological images. I have only minor comments – I think the ms should generally be accepted as it is.”

Reviewer 2 (that’s me): “This is a strong paper that brings an important new insight into a long-running palaeobiological issue [...] and should be published in essentially its current form.”

Reviewer 3: “This manuscript reports exciting results regarding sauropod biomechanics [...] The only significant addition I feel necessary is to the concluding paragraph.”

So imagine my surprise when the decision letter said:

I am writing to inform you that your manuscript [...] has been rejected for publication in Biology Letters.

This action has been taken on the advice of referees, who have recommended that substantial revisions are necessary. With this in mind we would like to invite a resubmission, provided the comments of the referees are taken into account. This is not a provisional acceptance.

The resubmission will be treated as a new manuscript.

I can’t begin to imagine how they turned three “accept with very minor revisions” reviews into  “your manuscript has been rejected … on the advice of referees, who have recommended that substantial revisions are necessary”.

In fact, let’s dump the “I can’t imagine how” euphemism and say it how it is: “reviewers recommended substantial revisions” is an outright lie. The reviewers recommended no such thing. The rejection can only be because it’s what the editor wanted to do in spite of the reviewers’ comments not because of them. It left me wondering why I bothered to waste my time offering them an opinion that they were only ever going to ignore.

Then six days ago I heard from the lead author, who had just had a revised version of the same manuscript accepted. (It had not come back to me for review, as the editor had said would happen with any resubmission).

The author wrote to me:

The paper will be published (open access) at the 3rd of Octobre. When I had submitted the corrected version of the ms acceptance was only a formality. So [name] was right, they just want to keep time between submission and publishing date short.

Well. We have a word for this. We call it “lying”. When the editor wrote “your manuscript [...] has been rejected for publication in Biology Letters … With this in mind we would like to invite a resubmission … This is not a provisional acceptance. The resubmission will be treated as a new manuscript”, what she really meant was “your manuscript [...] has been provisionally accepted, please sent a revision. The resubmission will not be treated as a new manuscript”.

I find this lack of honesty disturbing.

Because we’re not talking here about some shady, obscure little third-world publisher that no-one’s ever heard of with fictional people on the editorial board. We’re talking about the Royal Freaking Society of London. We’re talking about a journal (Biology Letters) that was calved off a journal (Proceedings B) that emerged from the oldest continuously published academic journal in the world (Philosophical Transactions). We’re talking about nearly three and a half centuries of academic heritage.

And they’re lying to us about their publication process.

When did they get the idea that this was acceptable?

And what else are they lying to us about? Can we trust (for example) that when editors or members submit papers, they are subjected to the same degree of rigorous filtering as every other submission? I would have assumed that, yes, of course they do. But I just don’t know any more.

Sampled specimens, sampling locations and cross sections of sauropod cervical ribs. (a) Anterior neck of Brachiosaurus brancai (Museum für Naturkunde, Berlin) with hyperelongated and overlapping cervical ribs. (b) Three cross sections were taken along the proximal part of the posterior process of a left mid-neck cervical rib of Mamenchisaurus sp. (SIPB 597) in ventral view. Note the medially pointed ventral part of the cervical rib. (c) Seven cross sections were taken along the left ninth cervical rib of B. brancai (MB.R.2181.90), which is figured in lateral view. (d) Neck of Diplodocus carnegi (cast in the Museum für Naturkunde, Berlin) with short cervical ribs. (e) Six cross sections were taken along the right mid-neck cervical rib of cf. Diplodocus sp. (Sauriermuseum Aathal, Aathal HQ2), which is figured in ventral view. Note the morphological differences of this cervical rib when compared with the hyperelongated cervical rib of B. brancai. (Klein et al. 2012:figure 1)

The paper in question is Klein et al.’s (2012) histological study confirming that the bony cervical ribs of sauropods are, as we suspected, ossified tendons — as we assumed in our recently arXiv’d sauropod-neck paper. I am delighted to be able to say that it is freely available. At the bottom of the first page, it says “Received 21 August 2012; Accepted 13 September 2012″, for a submission-to-acceptance time of 23 days. But I know that the initial submission — and remember, the final published version is essentially identical to that initial submission — was made before 17 July, because that’s when I was asked to provide a peer-review. Honest reporting would give a submission-to-acceptance time of 58 days, which is two and a half times as long as the claimed figure.

Now the only reason for a journal to report dates of submission and acceptance at all is to convey the speed of turnaround, and lying about that turnaround time completely removes any utility those numbers might have. It would be better to not report them at all than to fudge the data.

This is another way that the high-impact fast-turnaround publishing system is so ridiculously gamed that it actually hurts science. We have the journal lying to authors about the status of their manuscripts so that it can then lie to the readers about its turnaround times. That’s deeply screwed up. And it’s hard for authors to blow the whistle — they don’t want to alienate the journals and the editors who have some veto power over their tenure beans, and reviewers don’t usually have all the information. The obvious solution is to make the peer-review process more open, and to make editorial decisions more transparent.

That, really, is only what we’d respect from the Royal Society. Isn’t it?

Note. Nicole Klein did not know I was going to post about this. I want to make that clear so that no-one at the Royal Society thinks that she or any of her co-authors is making trouble. All the trouble is of my making (and, more to the point, the Royal Society’s). Someone really has to shine a light on this misbehaviour.

Update (12 March 2014)

I should have noted this before, but on 10 May 2013, the Royal Society sent me an update, explaining some improvements in their process. But as noted in my write-up, it doesn’t actually solve the problem. Doing so would simply require giving three dates: Received, Revised and Accepted. But as I write this, new Proc. B articles still only show Received and Accepted dates.

Reference

Subsequent posts discuss how this issue is developing:

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:

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 view, when placed as in position in the body. Capit. capitulum; Sh. shaft; Tub. tuberculum. Reconstructed portion in outline (Osborn and Mook 1921:fig. 71)

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 — orthoganal 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

On the off chance that the postparapophyses of Shunosaurus weren’t enough to sate your appetite for Sino-pod rib-related weirdness, here are a couple of fused cervicals of Klamelisaurus, from the Middle Jurassic of China (from Zhao 1993:plate 1). These are weird for a couple of reasons. First, although fused caudals are pretty common in sauropods (see here), and fused dorsals turn up a lot (see discussion here), and the fusion of the atlas to the axis is not unheard of (see here and here), fusion of the middle or posterior cervicals is rare. Which makes intuitive sense–presumably fusing up your food-reaching organ is counterproductive. The only other example I know of is the pair of fused posterior cervicals in the AMNH 5761  Camarasaurus supremus (which, oddly enough, I don’t think we’ve covered yet on SV-POW!). If you know of others, please let me know.

Anyway, what’s really weird about the Klamelisaurus verts is not the fusion but the bar of bone connecting the cervical rib of the first vertebra back to one or more of the centra. I think that the weird pseudo-parapophysis-thingy is not the parapophysis of the second vert, which is hanging down just behind, but some kind of extra ossification off the postero-ventro-lateral corner of the first vert’s centrum. Admittedly, that’s a lot of interpretation to hang on one grainy photo of a specimen I’ve never seen. But I’ve seen something similar in some bird cervicals, where there is sometimes  a prong or hook of bone from that corner of the centrum sweeping down and out to brace against the longus colli ventralis tendon that comes  off the cervical rib. One of the Apatosaurus cervicals on the wall at Dinosaur National Monument has a similar pair of hooks on its posterior centrum. Irritatingly, I don’t have any digitized photos of the Apato vert, and I can’t find any photos at all that show what I’m talking about in birds. Sorry to tantalize, I learned it from Darren. When I get pix, I’ll post ‘em.

In the meantime, you can amuse yourself by pondering the strangeness of the fused Klamelisaurus verts, and by watching the Dinosaur National Monument Quarry Visitor Center get demolished here.

Reference
Zhao X. 1993. A new mid-Jurassic sauropod (Klamelisaurus gobiensis gen. et sp. nov.) from Xinjiang, China. Vertebrata PalAsiatica 31(2):132-138.

It’s a strange thing, but no-one seems to bother properly figuring their sauropods’ cervical ribs — that is, the long, thin, posteriorly directed ribs of the neck vertebrae.  I’ll be bucking that trend when the Archbishop paper comes out, but to get your mouth watering ahead of time, here is the head of the cervical rib that I have arbitrarily designated X1, the largest of those preserved in the Archbishop:

Brachiosauridae incertae sedis NHM R5937, "The Archbishop", cervical rib X1. Preserved portion is 32 cm long.

The top image shows the rib in anterior view, with dorsal pointing to the left; the middle row shows the rib with anterior pointing upwards, in (from left to right), lateral, dorsal, medial and ventral views; the bottom row shows posterior view, again with dorsal to the left.  Click through the image to see the full glory of the high-resolution version.  Remember folks: you only get this sort of high-resolution image published in PLoS journals!

As I mentioned, sauropod cervical ribs have been pretty comprehensively ignored in the literature.  I can’t offhand think of a single paper about them (unless you count Martin et al.’s (1998) proposal that they functioned in ventral compression-bracing of sauropods’ necks, and let’s not even start on that), and I am really struggling to think of paper that figures them.  Even the usually super-reliable Osborn and Mook (1921) dropped the ball here, with a single illustration (out of 127 figures) and single short paragraph of text (out of 141 pages).  Here it is:

Cervical rib of Camarasaurus supremus AMNH 5761-a/R-X-A-5, from Osborn and Mook (1921:fig. 36) and accompanying text

Janensch (1950) did discuss the cervical ribs of Giraffatitan in some detail, but his figures are not very informative.  If anyone knows of better treatments of sauropod cervical ribs in the literature, then please mention it in the comments!

Because of this poor coverage in the published record, it’s hard for me to compare the Archbishop cervical ribs with those of other taxa.  For example, the medial view of X1 (in the middle of the “cross” in the image above) shows that the internal face of the cervical rib loop, where the cervical rib reaches up to articulate with the diapophysis of its vertebra, has two parallel struts of bone extending vertically with a narrow groove between them.  Is that unusual?  I have no idea.

(I do have photos of some other Tendaguru cervical ribs, referred to Giraffatitan – although if I’m right that the Archbishop is not Giraffatitan, so that there are multiple brachiosaurs in the Tendaguru Formation, then who knows whether that referral is correct?)

Finally, we come to the matter of your cervical ribs.  I would have liked to do this post as one in the Your Noun Is Adjective series, but the brutal truth is, you don’t even have any cervical ribs — unless you are one of the lucky 0.2% that, according to the Wikipedia article, have a supernumary rib which is frankly just an additional dorsal rib (uh, thoracic rib I guess) that’s growing out of your last cervical vertebra by mistake.  (Wikipedia’s horrible humanist bias is apparent here, in that the article doesn’t even mention the fact that plenty of other animals have cervical ribs and love them.)

Anyway, here’s how human cervical ribs look, stolen from Do You Really Need Back Surgery? A Surgeon’s Guide to Neck and Back Pain and How to Choose Your Treatment:

Cervical ribs in humans

References

  • Janensch, Werner.  1950.  Die Wirbelsaule von Brachiosaurus brancai.  Palaeontographica (Suppl. 7) 3:27-93.
  • Martin, John, Valérie Martin-Rolland, and Eberhard (Dino) Frey.  1998.  Not cranes or masts, but beams: the biomechanics of sauropod necks.  Oryctos 1:113-120.
  • Osborn, Henry Fairfield, and Charles C. Mook.  1921.  Camarasaurus, Amphicoelias and other sauropods of Cope.  Memoirs of the American Museum of Natural History, n.s. 3:247-387, and plates LX-LXXXV.

Taco

This is a taco.

Corndog

This is a corn dog.

Vertebra outlined in green. Click for unmarked original.

Vertebra outlined in green. Click for unmarked original.

Here’s a cross-section of a human. In the terms of fast food, people are corndogs. Most of us even have an outer ring of yellow adipose ‘breading’.

Vertebra oulined in red. Click for unmarked original.

Vertebra oulined in red. Click for unmarked original.

Here’s a cross-section of a cow. In an example of function following form, cows are, and often become, corndogs.

Note that in both the human and the cow the spaces between the neural spine and transverse processes are completely filled with back muscles, which in fact bulge out beyond the tips of the neural spine, as we also saw here. This despite the common paleoart convention of presenting dinosaurs as thin layers of skin conforming perfectly to the underlying skeleton. Just Say No to shrink-wrapped sauropods!

Diplodocus torso xs

Here is Figure 17 from Holland (1910), one of the most badass scientific smackdowns ever published, in which Holland wiped the floor with Hay, Tornier, and the idea of sprawling sauropods. On the left are torso skeletons of three lizards and a croc; on the right is an anterior dorsal with articulated ribs from Diplodocus. As you can see, it’s a taco, and its taconic form would be perfected if it could roll supine.

The point of the post is not that sauropods had deep, slab-sided bodies. We’ve covered that before. The point is that sauropod torsos are seriously weird. In mammals, the dorsal ribs arch up and out, away from the vertebra, before sweeping around to define the anterior body wall.  In lizards, the proximal part of each rib sticks out sideways. In sauropods, the ribs point down. This is mainly because the vertebrae are FREAKIN’ HUGE compared to the size of the body. Whereas in the mammals and lizards the dorsal vertebrae are titchy little things that span a small fraction of the width of the torso, in Diplodocus and other sauropods the dorsal vertebrae account for about half. (The cow cross-section missed the transverse processes, so that vert looks narrower than it actually is.)

This is relevant when we think about the function of pneumaticity. When I write that pneumaticity lightened vertebrae, I usually mean relative to that same vertebra if it wasn’t pneumatized. But we could also ask if the pneumatic vertebra is lighter than a vertebra from a similar-sized animal that lacks pneumaticity–except that, for big sauropods, there are no similar-sized terrestrial animals without pneumaticity to compare.

Imagine that in a big sauropod the dorsal vertebrae are three times as wide and three times as tall as they would be in a similar-sized mammal. They should weigh nine times more. But let’s also assume that the vertebrae of the sauropod are 85% air by volume, which is in fact pretty typical for Early Cretaceous brachiosaurids. The mass of the dorsal column relative to that of the mammal is then 9 x 0.15 = 1.35, a little heavier, but not much (I’m assuming the length of the torso is the same in the two animals). Bigger bones mean better lever arms for the muscles and lower bending stresses on the ribs, which can function more like curtains and less like cantilevered beams.

I can’t think of much published discussion of this stuff as it relates to sauropods, but it seems like it might be important.

Reference

Holland, W.J. 1910. A review of some recent criticisms of the restorations of sauropod dinosaurs existing in the museums of the United States, with special reference to that of Diplodocus carnegiei [sic] in the Carnegie Museum. American Naturalist 44:259-283.

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