Sauropods were corn-on-the-cob, not shish kebabs

June 25, 2009

This is corn on the cob:

Corn on the cob, in cross section, stolen from http://www.istockphoto.com/file_thumbview_approve/214165/2/istockphoto_214165-co rn-cob-cross-section.jpg

Corn on the cob, in cross section. Stolen from http://www.istockphoto.com/file_thumbview_approve/214165/2/istockphoto_214165-co rn-cob-cross-section.jpg

This is a shish kebab:

Most tetrapods are like shish kebabs: a whole lot of meat stuck on a proportionally tiny skeleton.  If you don’t believe me, you can look at the human and cow neck torso cross-sections in Matt’s last post, or check out this ostrich-neck cross-section from his 2003 Paleobiology paper:

Ostrich neck in cross section, CT scan.  From Wedel (2003a: fig. 2)

Ostrich neck in cross section, CT scan. From Wedel (2003a: fig. 2)

Remember that this is a freakin’ ostrich — of all extant animals, one of the ones with a most extreme long, skinny neck.  And yet, if sauropods were muscled like ostriches, then their necks would have looked like this in cross section:

Putative shish kebab-style sauropod neck in cross section.  Ostrich soft-tissue from Wedel (2003a: fig. 2), Diplodocus vertebra cross-section from Paul (1997: fig. 4) scaled to match size of ostrich vertebra

Putative shish kebab-style sauropod neck in cross section. Ostrich soft-tissue from Wedel (2003a: fig. 2), Diplodocus vertebra cross-section from Paul (1997: fig. 4) scaled to match size of ostrich vertebra

And soft-tissue reconstructions would have to look like this:

Diplodocus with its neck as fat as an ostrich's.  Modified from Paul (1998: fig. 1F)

Diplodocus with its neck as fat as an ostrich's. Modified from Paul (1998: fig. 1F)

Which, happily, no-one is suggesting.  Instead, published reconstructions of sauropod neck soft-tissue are startlingly emaciated.  As exhibit A, I call this pair of Greg Paul cross-sections:

Diplodocus and Brachiosaurus neck cross-sections, showing very light musculature.  From Paul (1997: fig. 4)

Diplodocus and Brachiosaurus neck cross-sections, showing very light musculature. From Paul (1997: fig. 4)

(Yes, the Diplodocus on the left is the one I used in the photoshopped ostrich cross-section above.  It’s instructive to compare Paul’s original with the What If It Was Like A Big Ostrich version.)

Paul’s reconstructions seem to be widely considered too lightly muscled.  But even the very careful and rigorous more recent reconstructions of Daniela Schwarz and her colleague show a neck much, much thinner than that of the ostrich:

Diplodocus neck cross-sections.  From Schwarz et al. (2007: fig. 7a)

Diplodocus neck cross-sections. From Schwarz et al. (2007: fig. 7a)

Although Schwarz has put a lot more soft tissue onto the neck vertebrae than Paul did, it is still a tiny proportion of what we see in extant animals — even the ostrich, remember, which has a super-thin neck compared with pretty much anything else alive today.  If sauropod necks were muscled as heavily as those of, say, cows, then the soft tissue would pretty much reach down to the ground.  But they weren’t: they were more like corn on the cob, with a broad core of skeleton and relatively little in the way of delicious edibles festooned about it.

So why is this?  Why does everyone agree that sauropod necks were much less heavily muscled than those of any extant animal?

It’s a simple matter of scaling.  A really big ostrich might have a neck 1 m long.  (Actually, ostriches don’t get that big, but let’s pretend they do because it makes the maths easier).  If the x meter-long neck of a sauropod was just a scaled-up ostrich neck, then it would be x times longer, x times taller and x times wider, for a total of x^3 times as voluminous and therefore x^3 times as heavy.  But the cross-sectional area of the tension members that support it is only x times taller and x times wider, for a total of x^2 times the strength.  In total, then, the neck’s mass/strength is x^3/x^2 = x times as great as in the ostrich.  (The sauropod neck’s mass also acts further out from the fulcrum by an additional factor of x, but that is cancelled by the fact that the tension in the neck also acts x times higher above the fulcrum.)

It seems intuitively obvious (which is is code for “I have no way to prove”) that you can’t reasonably expect the neck muscles of a giant ostrich to work ten times as hard as they do in their lesser cousins, which is what you’d need to do for the 10 m neck of, say, Sauroposeidon.  So simple isometric scaling won’t get the job done, and you need to restructure the neck.

But how?  Surely just reducing all the muscle around the vertebrae can’t help?  No indeed — but that is not really what sauropods were doing.  If you look at the typical sauropod-neck life restoration, you’ll see that the proportional thickness of the neck is actually not too dissimilar to that of an ostrich — rather thicker, in fact.  If you scaled an ostrich neck up to sauropod size and compared it with a real sauropod neck, you would find not that the soft tissue was too fat, but that the vertebrae were too thin.

And so we come to it at last: rather than thinking of sauropods as having reduced the amount of soft-tissue hanging on the cervical vertebrae, we do better to think of them as having kept a roughly similar soft-tissue profile to that of an an ostrich, but enlarging the vertebrae within the soft-tissue envelope.  Of course if you just blindly made the vertebrae taller and wider, they would become heavier in proportion, which would defeat the whole purpose of the exercise — but as everyone who reads this blog surely knows by now, sauropod cervicals were extensively lightened by pneumaticity.  By bringing air into the center of the neck, they were effectively able to displace bone, muscle and ligament away from the centre, so that they acted with greater mechanical advantage: higher epaxial tension members, lower hypaxial compression members, and more laterally positioned paraxials.

It’s a rather brilliant system — using the same volume of bone to achieve greater strength by displacing it outwards and filling the center with air (and, in doing so, also displacing soft tissue outwards).  And it will be hauntingly familiar to anyone who loves birds, because it is of course exactly what birds (and pterosaurus) have done in their long bones: the hollow humeri of flying vertebrates famously allow them to attain greater strength — specifically, resistance to bending — for the same volume and mass of bone.  It’s a neat trick when done with long bones, but it takes a truly awesome taxon to do it with the neck.

So maybe sauropods were not corn on the cob after all.  Maybe they were Hostess Twinkies.

Hostess Twinkie.  Not truly pneumatic, as the internal cavity is filled with adipose tissue rather than air, but do you have any idea how difficult it is to find good images of hollow junk food?

Hostess Twinkie. Not truly pneumatic, as the internal cavity is filled with adipose tissue rather than air, but do you have any idea how difficult it is to find good images of hollow junk food? Stolen from http://dixiedining.files.wordpress.com/2008/07/twinkie_070918_ms1.jpg

And now for something completely different

Now that I’ve finished my Ph.D at the University of Portsmouth, what am I going to do with the rest of my scientific life?  I’ve always said that I have no intention of going into palaeo full time: my knowledge is far too narrow for that, so that even if paid jobs were not in insanely short supply, I wouldn’t stand much chance of getting one.  And in any case, I’d hate to get into the all-too-common situation of being up against a friend for a position we both wanted. Throw in the fact that I really enjoy my computer-programming day-job and it seems pretty clear that what I need is an unpaid affiliation that lets me get on with lovely research.

Well: I am absolutely delighted to announce that, as of last month, I am an Honorary Research Associate in the Department of Earth Sciences at UCL.  It’s not just that UCL is such a well-respected institution — see that Wikipedia article for some details — more importantly, it’s where Paul Upchurch hangs out, as Senior Lecturer in Palaeobiology.  Sauropod fans will be familiar with Paul’s characteristically detailed and careful work, from his pioneering work on sauropod phylogeny (Upchurch 1995, 1998), through his and John Martin’s indispensible Cetiosaurus makeovers (Upchurch and Martin 2002, 2003) to the state-of-the art review that he lead-authored for Dinosauria II (Upchurch et al. 2004) and the Tokyo Apatosaurus monograph (Upchurch et al. 2005).  What many of you won’t know is what an excellent collaborator he is — quick, conscientious, insightful and diplomatic.  We’ve already collaborated on a few short papers (Upchurch et al. 2009 and a couple of Phylocode companion-volume chapters that are in press), and I hope there will be more in the future.

References

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25 Responses to “Sauropods were corn-on-the-cob, not shish kebabs”

  1. Heinrich Mallison Says:

    Good post :) It’s what the FOR 533 in general and Preuschoft, Christian and I have been saying (but not writing, us lazy ba*tards) for a while: the trick about sauropods is that they use air to increase size (thus, in this case, moment arms) without increasing mass. Allows them to ignore the old ‘cube of the root’ problem of scaling. This is not only true of the neck, but also of the guts: doubling the length, width and height of the trunk does NOT result in the cube of the mass, but only in something slightly bigger than the square, so that the volume of the guts can expand proportionally more than the mass of all the other tissues (verts, ribs, muscles). Thus, overall, energy gain from digestion per kg of total animal mass is proportionally higher than it would be without air sacs and pneumaticity. That may be the key factor behind the extreme size of sauropods!

  2. Mike from Ottawa Says:

    “It’s a rather brilliant system …”

    And a rather brilliant explanation, bearing the hallmark of brilliance: seeming glaringly obvious once someone else has pointed it out.

    And, congratulations on landing the gig at UCL. Looks ideal for someone who is the epitome of the best sense possible of the word “amateur”.

    BTW, did you try looking for pictures of a Nestle Aero bar?

  3. Nathan Myers Says:

    First, I thought Matt’s cross-sections were of torsos, not necks. Don’t I spy kidneys and guts in there?

    Second, surely you could find some shots of half-eaten croissants? (Mmmm, croissants.)

    Finally, one way we see animals operate extremities where, for whatever reason, muscles would be inconvenient is to extend tendons out there and put the muscles somewhere else. For an example, look to your hand, with the muscles mostly bunched, Popeye-like, in your forearm. In your hand, the muscles would get in the way and be exposed to damage. In the sauropod neck, the problem with muscles is weight, weight easily accommodated centrally.

    If the sauropod neck worked like your hand, we might expect the sauropod to channel bundles of tendons up the neck, with the muscles to operate them bunched mostly above the thorax. It could operate, instead, with one big tendon extending the length of the neck, gripped at each flex point. A given neck posture would be obtained by fixing the distal points first, proceeding proximally. (Does a flamingo neck work this way?) Probably using two (or a few) tendons, one for distal adjustments, another for proximal motion, would yield more practical results.

    Congratulations on your appointment at UCL. It’s amazingly hard to find from their website, by the way, what the “UCL” stands for, so I will reveal here that it means “University College London”.

  4. Julia Says:

    Nice one Mike – so we might see a bit more of you in London, and even perhaps the odd appearance at Journal Club? ;-)

    And you now have access to the Housman Room, which is the closest thing to a London club that most academics will ever have!

  5. Mark Evans Says:

    Congratulations Mike, UCL was a fun place (I’m sure it still is).

  6. Heinrich Mallison Says:

    >>Nathan Myers Says:

    >>If the sauropod neck worked like your hand, we might expect the sauropod to channel bundles of tendons up the neck, with the muscles to operate them bunched mostly above the thorax. It could operate, instead, with one big tendon extending the length of the neck, gripped at each flex point. A given neck posture would be obtained by fixing the distal points first, proceeding proximally. (Does a flamingo neck work this way?) Probably using two (or a few) tendons, one for distal adjustments, another for proximal motion, would yield more practical results.<<

    Sorry, Nathan, as nice and effective as that sounds, it would make the neck totally useless. How, after all, would you create a S-curve? And if you can't do so, how would you feed effectively? (wait for my paper…) ;)

  7. Nick Gardner Says:

    “First, I thought Matt’s cross-sections were of torsos, not necks. Don’t I spy kidneys and guts in there?”

    No. You don’t.

  8. Nathan Myers Says:

    Nick: “First, I thought Matt’s cross-sections were of torsos, not necks. Don’t I spy kidneys and guts in there?” No. You don’t.

    Still, that’s a torso, not a neck, and what is that stuff if not guts? The image is labeled “human-abdomen-xs.jpg”. Anyway, what are those matched light-brown ovals?

    Heinrich: How would you create an S-curve? I addressed that with the remark about two tendons. (With one tendon I suppose it would have to start by laying its neck over the back of a fellow sauropod, or be clever with peristaltic operation of the clamps.) I have long been waiting eagerly for your paper, without even knowing of it.

  9. Matt Wedel Says:

    Nick: “First, I thought Matt’s cross-sections were of torsos, not necks. Don’t I spy kidneys and guts in there?” No. You don’t.

    I didn’t follow that either. Perhaps there is some confusion about which cross-sections were talking about? The ones in my post (tacos not corn dogs) definitely are torso sections and show guts. Good spot on the kidneys in particular.

  10. Heinrich Mallison Says:

    Nathan:

    for an S-curve you need bundles of tendons – not just two. If that’s what you meant (and now, reading your post again, I see that you probably did) I take everything I said back and assert the opposite :)

  11. Zach Miller Says:

    Mmmm…twinkie-pods.

  12. Caitlan Says:

    “higher epaxial tension members, lower hypaxial compression members, and more laterally positioned paraxials.” Ooooh myyy godddd. 10 minutes ago I would not have been able to come up with even one word ending in “axial”.

  13. Nima Says:

    I have a funny hunch you guys have another food-related sauropod post coming up… if so, this would make a good series to link to (sort of the “your noun is adjective” series)

    One thing that looks a bit odd (aside from the crazy-tall ligament stippled that Paul stippled in for Brachiosaurus) is the esophagus and the trachea being side by side (instead of one behind the other)in Paul’s cross sections. This side-by-side configuration certainly LOOKS like it would make sense for space efficiency, but does it actually happen in living animals?

  14. Matt Wedel Says:

    All right, I finally figured out the source of the torso/neck confusion: I hadn’t realized that Mike referred to the cross sections in the last post as neck sections, when in fact they are from the torso in both cases. He also misspelled the title of the journal Paleobiology with an extra ‘a’, and didn’t include links to any of the freely available references (all these problems are now fixed). That’s three strikes, good buddy–you’re out!

    Nima, in birds the trachea is very mobile and can slide around all over the place. Sometimes it is ventral to the esophagus, but it is just as likely to be lateral or even dorsolateral to the esophagus and even the vertebral column. See the budgie from the “Necks Lie” post for an example. There are loads of radiographs of birds that show this, too–I’ll try to remember to post one soonish. Anyway, it’s not unreasonable to depict sauropod tracheas displaced away from the midline, although it’s certainly jarring to our mammalian sensibilities!

  15. Nick Gardner Says:

    http://svpow.wordpress.com/2009/06/25/sauropods-were-corn-on-the-cob-not-shish-kebabs/#comment-3466

    Yes, I thought we were talking about the cross sections in this post, not the other one. ;-)

  16. Nathan Myers Says:

    Nick, you have a lot to answer for. I doubt you can get off without producing a full-on guest article.

  17. Casey Holliday Says:

    The emaciated/meatless dinosaur phenomenon is common in head reconstructions too where one can undoubtedly make out fenestrae, bony orbit margins, etc. in many artistic renditions. The skin and underlying soft tissue often cover over those bony features leaving more or less a smooth surface across landmarks.

  18. David Marjanović Says:

    The emaciated/meatless dinosaur phenomenon is common in head reconstructions too where one can undoubtedly make out fenestrae, bony orbit margins, etc. in many artistic renditions.

    Worse yet: if at all, all those features should bulge out, yet they do the opposite in most artistic restorations.


  19. [...] a strange thing: although I’ve been affiliated with UCL for eighteen months now, I’ve never got around to setting up my off-campus institutional [...]


  20. [...] we’ve discussed before, the necks of most sauropods were not round in cross section (see here and here). The cervical ribs stuck out far enough ventrolaterally that even with a lot of muscle, [...]


  21. [...] of fun and very productive. But they did mean that between the scheduled activities and getting a big manuscript finally submitted, I’ve been very much out of touch, and I’m only now catching up with [...]


  22. [...] paper incorporates some material from SV-POW! posts, including Sauropods were corn-on-the-cob, not shish kebabs. In fact, come to think of it, we should have cited that post as a source. Oh well. We do cite one [...]


  23. [...] of historical SV-POW! posts that could have been PeerJ articles on their own — for example, the shish-kebab post that ended up as part of Why Giraffes Have Short [...]


  24. […] at #34, “corn dog” at #42 and “corn on the cob” at #77 (probably all due to the same post on sauropod neck fatness). Rather sadly, “big ass” comes in at #89. I doubt that the 602 people who came here by […]


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