Sauropods were tacos, not corn dogs

June 22, 2009

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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23 Responses to “Sauropods were tacos, not corn dogs”

  1. Tor Bertin Says:

    Very much agreed on the paleo art front… for some reason, that’s always annoyed me.

    Also, a random thought (not a hypothesis, haven’t put nearly as much thinking into its possibility ;-) ). Could the design of the sauropod’s torso also have something to do with the infamous blood pressure issue?

    In other words, is it also possible that the surface area of the torso was reduced to lessen the degree of blood flow needed to keep the full animal operating?

  2. Zach Miller Says:

    Diplodocus! Go fix yourself a kesa-dilla!

  3. Nathan Myers Says:

    Here’s me predicting that agonization over (and avoidance of) the “blood pressure issue” will dissipate once it’s realized that there is no other solution to it than something like peristalsis in the cervical arteries.

  4. Tor Bertin Says:

    That’d be pretty neat.

    I’d imagine that the timing of the contractions would have to be superb to avoid any kinds of blockages (if it’s too off time with the heart’s beat, all sorts of weird things would happen).

  5. Nima Says:

    Mmmmmmm….. tacos!

    No wonder we all hate those bone-scatterin’ stinkin’ theropods so much… we’ll never get to taste such massive tacos :(

    But yeah, sauropods had some seriously reinforced backs.


  6. “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”

    Not to disparage the general point (re:don’t illustrate anorexic dinosaurs) but to try and prevent a massive over-correction by illustrators, it should be noted that mammals have a rather unusually derived form where they exploit dorsoventral movement in the vertebral column more than other organisms, and so they have particularly heavily-muscled trunks primitively. Sprawling animals also have a decent chunk or trunk muscles since they have to oppose lateral undulation when it’s unwanted, and instigate it when it is.

    Dinosaurs do not fit either of these molds, being upright organisms (sometimes graviportal) with stiffer backs than most of the animals discussed above. Birds (which are not a perfect analogy for sauropods either) even with their much shorter neural spines do show a separation between the neural spine muscles and the other trunk muscles (albeit a rather subtle one) once the feathers are removed, e.g. http://www.nextnature.net/research/wp-content/uploads/2006/10/chicken3~.jpg and http://farm2.static.flickr.com/1139/639793049_dabcb52243.jpg?v=0

    So by all means, if you haven’t all ready let’s start illustrating our dinosaurs where the illiocostalis and the cervical musculature make more obvious contours than the medial dorsal musculature, I just don’t want the reaction to be animals draped in formless flesh…that’s not what most vertebrates look like unless they have that nice “bread/adipose” layer covering their “corn dog” torsos. Even healthy humans and cows have contours from their axial musculature that are visible.

    K, sorry, soap box disengaged.

  7. Zach Miller Says:

    Sheesh, can you imagine that pain a sauropod would be if one of its disks collapsed? Ouch. I think I’M in pain…


  8. Er… so what do you think of the new JVP paper on the topic?

    Schwarz-Wings, 2009. RECONSTRUCTION OF THE THORACIC EPAXIAL MUSCULATURE OF DIPLODOCID AND DICRAEOSAURID SAUROPODS. Journal of Vertebrate Paleontology. 29(2):517–534.

  9. Nima Says:

    yeah Zach, imagine having to do surgery on one of those things! The blood loss would be crazy.

    Perhaps disk injury may be the main reason behind fused sauropod vertebrae (either that or some pathology or just old age…)

  10. Brian Beatty Says:

    I’m not sure I would make the taco comparison, as I suspect that even if sauropods had reduced trunk motility, they would still have muscles of sufficient thickness that connect their limb girdles to the axial skeleton that they’re fairly “meaty”.
    But I agree that they seem seriously, seriously weird. There was a student at KU some years ago studying sauropod rib anatomy in some depth (Jaqueline Wood), though I am not sure what she has published of it. Considering the excitement over other aspects of sauropod postcrania, I wouldn’t be surprised if someone out there is looking at their ribs now – I hope!

  11. Matt Wedel Says:

    Hi all. Mickey, I just got my JVP yesterday and I haven’t read Daniela’s paper in detail yet, but I have skimmed it and I saw her give a presentation on this work in Bonn last fall. It looks convincing to me. The obvious problem is the same one that I have with pneumatic features on the external surfaces of vertebrae: the soft tissues lateral to the verts and dorsal to the ribs are only bounded by bone on one side, and we don’t know how much they bulged up or out. So for some of these things we can reconstruct where the pneumatic diverticula or muscles were, but we have no way of knowing how fat (voluminous) they were.

    Which ties in with Scott’s point–which is well taken–about the likely differences in back muscles between dinosaurs and mammals. It’s worth remembering that the deep, compact torsos of sauropods evolved from the longer, skinnier, more flexible (and more corn-doggy) torsos of prosauropods. AFAIK there has been little or no work done on the evolution of the torso as a unit in sauropodomorphs, and all too little work on the torso in dinosaurs in general.

    Which brings us to Brian’s comment. Yes, Jacqueline Wood is still working on sauropod torsos, and in fact she has a couple of papers in the works, so hopefully we’ll have some new and useful information in this area soon.

  12. Nathan Myers Says:

    Maybe Dr. Wood and a couple of like-minded colleagues can be persuaded to start a Sauropod Torso Picture of the Week blog, sister to this august body. Who will start the Sauropod Pelvis of the Week blog, though? Clearly it could not properly be sister to the others; I suppose it would have to be a sort of rump blog.

    But on to technical matters… keeping peristalsis in cervical arteries synchronized with the cardiac pulse ought to be easy enough, considering that the hydrostatic pressure pulses are easily sensed, operating at a very different frequency than the peristaltic waves.

    The hypertrophy and pneumatization of sauropod thoracic vertebrae seem a natural response to the incredible loads they carried. We may analogize that they expanded to form a space frame.

  13. Nima Says:

    Good point Nathan. A lot of these laminae were basically like natural I-beams. A strong spine is always essential for bigger animals. And a weight-saving strong spine, even more so.

    Sauropod pelvis? I think there just might be an audience for that! (if there were more solid ones to photograph besides the really common species).

  14. Matt Wedel Says:

    I’m not sure I would make the taco comparison, as I suspect that even if sauropods had reduced trunk motility, they would still have muscles of sufficient thickness that connect their limb girdles to the axial skeleton that they’re fairly “meaty”.

    I’m sorry, I wasn’t very clear in the post. My taco/corn dog comparison is intended to be about the shape of the torso as defined by the vertebrae and ribs, not about meatiness. Sauropod ribs pointed mostly down and a little out to side, whereas the ribs of most (all?) other tetrapods are more laterally or even dorsally directed where they come off the vertebral column.

    Can anyone think of another tetrapod group in which this is the case?


  15. “Can anyone think of another tetrapod group in which this is the case?”

    Theropods? Sure a few a few derived tetanurans have mid-dorsal ribs that stick out more to the side, but not primitiver theropods and never with the anterior ribs.

    Also, don’t derived macronarians have mid and posterior dorsal ribs that are oriented a lot more to the side rather than down (by sauropod standards, anyways)?

  16. DDeden Says:

    Question: Sauropods have large pneumantic vetrebrae, manatees have big super dense ribs, bony fish have mucho thin bones; so did early vertebrates (way before dinos) swim upside down with dense vertebrae as part-ossified ballast (like early turtle plastron), making them inverted invertebrates, then after developing an air sac flipped back right side up, then sauropods further lightened the vertebrae due to occasional (upright) shallow water wading and swimming? (I know ‘semi-aquatic dinos’ are old school, but I figure more primitive dinos were more water dependent, later ones much less so.)

    Corn dogs & tacos… awsum skwared!


  17. […] skeleton.  If you don’t believe me, you can look at the human and cow neck cross-sections in Matt’s last post, or check out this ostrich-neck cross-section from his 2003 Palaeobiology paper: Ostrich neck in […]

  18. David Marjanović Says:

    did early vertebrates (way before dinos) swim upside down with dense vertebrae as part-ossified ballast (like early turtle plastron), making them inverted invertebrates, then after developing an air sac flipped back right side up

    One word: Chondrichthyes.

    I figure more primitive dinos were more water dependent, later ones much less so

    You don’t figure. You pull out of thin air.

    And you don’t even notice how much you’re contradicting the fossil record.

  19. leopold Says:

    don’t know what you’re talking about, but “cows are, and often become, corndogs.” is great!


  20. […] 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 […]


  21. […] they were unusually deep and slab-sided, more so than in most other tetrapods (see this and this, and for a more pessimistic take, this). This is something that is easy to get wrong; we are used […]


  22. […] buts involved. The first is that a lot of sauropods had distinctly non-round body cross-sections (Diplodocus, Camarasaurus). So assuming circular cross-sections might inflate the body well beyond its likely […]


  23. […] (Previously: Sauropods were tacos, not corn dogs; and Sauropods were corn-on-the-cob, not shish kebabs.) […]


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