There’s almost nothing but nothing there, Sauroposeidon edition

September 23, 2008

Internal structure of a cervical vertebra of Sauroposeidon, OMNH 53062. A, parts of two vertebrae from the middle of the neck. The field crew that dug up the bones cut though one of them to divide the specimen into manageable pieces. B, cross section of C6 at the level of the break, traced from a CT image and photographs of the broken end. The left side of the specimen was facing up in the field and the bone on that side is badly weathered. Over most of the broken surface the internal structure is covered by plaster or too damaged to trace, but it is cleanly exposed on the upper right side (outlined). C, the internal structure of that part of the vertebra, traced from a photograph. The arrows indicate the thickness of the bone at several points, as measured with a pair of digital calipers. The camellae are filled with sandstone.

Image and caption recycled from fig. 14 here. Hat tip to Mike from Ottawa for the wonderful title.

Addendum (from Mike)

What Matt’s failed to mention is that this section of prezygapophyseal ramus is one of the elements for which he calculated the Air-Space Proportion (ASP) in his chapter in “The Sauropods”. As shown in his table 7.2, this calculation yielded 0.89.  Just think about that for a moment.  89% of the bone was air.  Yikes.

It’s interesting that this was the only prezygpapophyseal ramus in the survey, and that it had a way higher value that any of the other elements considered, which topped out at 0.77, i.e., more than twice as much bone as this specimen.  So maybe all prezyg rami are ridiculously pneumatic? So far (as far as I know) no-one’s measured the ASP of another ramus, so the answer remains, for now, ridiculously unknown to our planet.

Special bonus weirdness

Basal sauropodomorph wizard Adam Yates has posted an entry on his blog showing more sauropod vertebrae/ceratopsian frill convergence, as follow-up to our own recent post. Too weird.

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27 Responses to “There’s almost nothing but nothing there, Sauroposeidon edition”

  1. William Miller Says:

    89% air? Yowza.

    Are the vertebrae the only pneumatic bones, or is the whole skeleton airy? Could the lack of pneumaticity in big mammals be why none have gotten much over 10 tons on average?

  2. Mike Taylor Says:

    Two interesting questions :-)

    Plenty of animals (including you) have pneumatic bones in the skull, but if we ignore that, then skeletal pneumaticity is very rare — found only in saurischian dinosaurs (including birds) and pterosaurs. In birds, all sorts of crazy stuff gets pneumatised, including sternum, humeri, etc; but in sauropods, it’s only vertebrae and the occasional rib. BUT: not long ago, a lot of people would have said only vertebrae, and it’s really only since people started looking more carefully at ribs that their pneumatic features have been more widely recognised — from quite a few different sauropods including Apatosaurus, Supersaurus, both Brachiosaurus species and the as-yet-unnamed Hotel Mesa sauropod. Which makes me think: I wonder whether there might be other pneumatic bones out there that haven’t been recognised as such just because no-one’s looked at them while tuned to the correct wavelength? Put it this way: it would not shake my world if someone were spot, say, a pneumatic foramen in a macronarian ilium.

    Is pneumaticity what enabled sauropods to get so big? Actually, I don’t think so. It must have helped, of course, but not by that much. Matt’s 2005 book-chapter (linked above) worked though the probable volume of pneumaticity in Diplodocus (which is pretty pneumatic) and found that it only reduced total body mass by about 10% — so mammals should be able to reach 90% of sauropod size on that basis, which of course they don’t. Not even close. Perhaps not even 10%.

    So how _did_ sauropods get so big? Well, if I figure that out, I’ll submit it one of the extended-abstract tabloid journals (_Science_ ‘n’ _Nature_) rather than in a blog post :-)

  3. William Miller Says:

    Oh, sorry – I wasn’t suggesting that it made something like Brachiosaurus or Sauroposeidon as light as a mammoth or indricothere! I was just wondering if it gave them better strength-to-weight-ratio bones, and whether that might have a multiplicative effect on what the animal’s frame could hold. But if not, I suppose it remains a mystery…

  4. Nathan Myers Says:

    Actually 10% is a huge effect at that mass, because it’s multiplicative. When you don’t have to hold up that 10%, you need less muscle, and less bone to support the muscle and bone, etc. I wouldn’t be surprised to find that that 10% made it possible to be half again bigger, dimensionally, than they could have been otherwise. Without it, the crazy long neck might not have been possible at all.

    An indricothere half again bigger would be no challenge to sauropodia’s record. Perhaps whatever made it unprofitable to be a sauropod in the later Cretaceous also, analogously, made life tough for a big indricothere. This does raise (again!) the question of what advantage such hugeness ever conferred in the first place.

    When monkeyboys with sharp sticks can kill you just as easily regardless of how big you can get, the economics of size changes, as indeed it did.

  5. William Miller Says:

    As far as I know, the size problem is almost restricted to sauropods – the only non-sauropods I can find online which exceeded ten tons are, apparently, a couple big hadrosaurs – Shantungosaurus and Lambeosaurus laticaudus, and a few others, which have been estimated at 20+ tons. These are the bigger estimates, though, and numbers that big have been flung around for indricotheres and the biggest mammoths.

    So, the question is more “why did sauropods get so big?” than “why were dinosaurs so big?”. Perhaps the Jurassic ecosystem was more productive of plant food, and the warmer world was more homogeneous ecologically? Larger areas of the same biome, and a more stable climate, might have made the adaptability advatages of somewhat smaller size unnecessary?

    Now please tell me the errors in my uninformed ideas :)

  6. Nathan Myers Says:

    I can’t help thinking the neck must be a clue, so I look for an arms race, e.g. trees frantically growing taller than the sauropods could grow their necks to reach.

    Crucially, a longer spine offers more places to park defensive pterosaurs, providing an air power advantage. This would be the purpose of all those strange neural-spine structures. In other words, pterosaurs were not, as has been assumed, independent organisms at all; they were budded off the spines of sauropods as airborne long-range defensive organs. That’s why the pterosaurs declined in step with the the sauropods.

    The azhdarchids eventually dispensed with the free-walking sauropod mother stage, and grew directly from eggs, with only a vestigial sauropodesque yolk.

    Nigersaurus’s innovation was to grow light enough that its fleet of pterosaurs could carry it from place to place. Eventually it took up skimming pond muck from just above the water surface.

    Of course this establishes pterosaurs firmly within the charter of this blog, because the entire pterosaur body is properly seen, now, as part of a single sauropod vertebra.

    Now please acknowledge the superiority of my unhidebound ideas. :-)

  7. Matt Wedel Says:

    Hi, all. Your discussion got so interesting it lured me out of my hermit cell. So here goes: If you want my two cents, the two biggest limitations on mammals are food and babies.

    Elephants spend almost all of their waking time eating. Presumably as mammals get into the over fifteen-ton arena, food becomes limiting not because the environment doesn’t supply enough, but because they can’t consume it fast enough. But mammmals spend a lot of that “eating” time chewing, and big mammals chew less thoroughly than little ones. Look in elephant poop the next time you get the chance–you’ll see a LOT of undigested grass in there.

    Sauropods not only didn’t chew, they couldn’t. Their teeth didn’t occlude and they didn’t have cheeks to hold the food in anyway. Interestingly, prosauropods may have had cheeks that were later lost in sauropods, in which case sauropods might have once been capable of limiting chewing but ditched that ability on their evolution toward giant size. Anyway, no chewing = more time for packing in the chow.

    Going along with this, mammal heads tend to have big brains and big heavy teeth, and the ‘gape’ or cropping area of the mouth is actually pretty darn small. Whereas sauropods had heads like toilet seats, that were practically all mouth. Sauropod heads only look small because we’re used to seeing cropping area + chewing machinery + lotsa brains, and to a first approximation sauropod heads were just biting devices. A big brachiosaur would have had a head close to a meter long and half a meter wide, and almost all of that was mouth. If you wanted to find a mouth that big among mammals you’d have to go to a small cetacean.

    About babies. As mammals get bigger they make fewer babies and each one takes longer to produce. Elephants gestate for about two years to get a single calf. Not good for building up populations after the inevitable crashes (like the one we’re imposing on them). But as reptiles get bigger they make more eggs, so presumably the biggest sauropods made the most eggs. How that ties into sauropod paleoecology is not very well explored yet, but it was surely important.

    So to me, the question is not why did sauropods get so big, but why don’t mammals get bigger, and the answers are food and babies. That doesn’t tell us why birds don’t get bigger. It is true that eggs scale up and eventually the eggs get to be too big, but I’ve not heard an explanation for why that is true of birds even though it apparently wasn’t true of sauropods.

    Discuss.

  8. William Miller Says:

    Interesting.

    So, just to ask annoying but interesting questions: why were there no fifty-ton ceratopsians or hadrosaurs?

    As for food, would it make a difference that the Jurassic had a very different ecosystem?

  9. Matt Wedel Says:

    So, just to ask annoying but interesting questions:

    Nah, just interesting.

    why were there no fifty-ton ceratopsians or hadrosaurs?

    I say it’s because they chewed their food, and all that that implies.

    As for food, would it make a difference that the Jurassic had a very different ecosystem?

    Almost certainly! There was a talk at SVP a few years ago about how T. rex and other giant theropods couldn’t have been endotherms because they couldn’t have gotten enough food. I don’t buy it. Big predators are an epiphenomenon of big prey, and I think the big prey are at least partly explained by the probably high CO2 levels driving increased plant productivity. So trying to explain big predators by focusing on big predators is, to me, looking at the system from the wrong end.

    That’s not to say that cranking up the CO2 will necessarily produce sauropod- or even shantungosaur-sized herbivores and their attendant giant predators. But cranking up the CO2 in the presence of lineages that make more babies as they get bigger (unlike mammals) and don’t produce absurdly large eggs that rapidly become prohibitive (like birds) might explain a lot of why dinosaurs got big. For sauropods, add in the flip-top heads, no chewing, and pneumaticity to make long necks more feasible. I’d be shocked if that was the whole explanation–but I’ll be equally shocked if that handful of factors aren’t a big part of whatever the answer turns out to be.

    Feel free to tear all this apart. That’s apparently what the intertoobs are for. :-)

  10. William Miller Says:

    Ah, yes … that makes lots of sense.

    I think that explains the normal sauropods (is there any such thing?) quite well. Something like Amphicoelias, though … I bet there’s something else going on – that structure had to be incredibly well engineered. (If the fossil bone was *that* fragile, maybe it was incredibly pneumatic?)

  11. Matt Wedel Says:

    Yeah, maybe. The freaky thing about pneumaticity is that it can go a lot farther than you might think. That’s sort of the point of the post, but there are even weirder examples out there. There was a paper out a couple of years ago on the pneumatic “bone foam” inside a toucan’s beak, which is the lightest form of bone ever discovered. Working backward from the published density, I figure it must be upward of 95% air by volume, maybe 97-98%. That is scary.

    I really, really hope that some more of A. fragillimus comes to light some day, and if it does, I expect its level of pneumaticity to be seizure-inducing.

  12. Mike from Ottawa Says:

    ” ” why were there no fifty-ton ceratopsians or hadrosaurs? ”

    I say it’s because they chewed their food, and all that that implies. ”

    If growing big was A Good Thing and chewing gets in the way of growing big, why did large ceratopsians and hadrosaurs (and elephants and indricotheres) not give up chewing and become really, really big?

    Oh, and how pneumatic were pterosaurs by comparison? Or do I need to ask that at Pterosaur Skull Picture Of the Week?

  13. Nathan Myers Says:

    MfO: Since we’ve already established that pterosaurs were just hyperspecialized sauropod neural spines, any pterosaur topic is apropos here. (And nigersaurus was a skim-feeder.)

  14. William Miller Says:

    The question of why no giant birds is a really good one. Before I found this blog, I would have thought it was because of pneumatic bones, but obviously not.

    Maybe there has never been a time period when birds had a chance to grow without competition (flightless birds usually have trouble competing). New Zealand and Madagascar might not have been big enough to support sauropod-scale birds (I doubt that, though, because Sri Lanka has elephants). But even that wouldn’t explain why ostriches couldn’t outcompete giraffes as high browsers…

    Another uninformed question: do the pneumatic cavities in vertebrae line up when those vertebrae are articulated? If so, a sauropod spine could be structurally modeled as a pipe or hollow tube…

  15. Andreas Johansson Says:

    Might the lack of gigantic birds have something do do with bipedality? Large herbivores are mostly quadrupedal.

    Doesn’t explain why we don’t see tyrannosaur-sized killer chickens, mind. It’s a great shame, if you ask me, that there aren’t any elephantivorous mega-chickens around.

  16. Mike Taylor Says:

    The big question about elephants, for me, is why they are so pants at digesting. They have big guts — as big as some of the more negligible sauropods, so how is that they don’t do a good enough job to, for example, fully digest all the grass they eat? Talk about lame.

  17. Nathan Myers Says:

    Getting back to the subject of sauropods (if not, yet, vertebrae, but we’ll get there!), haven’t sauropod coproliths been found with fossilized grass in them? It is now well established (at least around here) that, lacking mammary glands, the sauropods had good, sound, and commendable reasons to eject partially-digested greenery, what with all the hungry little short-gutted sauropods swarming underfoot. But might not elephants have a similar motivation, on behalf of their recently weaned offspring?

    And weren’t the paleobotanists used to maintaining that grass was a post-Cretaceous development?

  18. DD Says:

    I feel like my brains are pneumatic when I enter this blogsite. I know so little about this stuff.

    A very pneumaticised bipedal dinosaur from Argentina, full of air sacs, is it comparable to the sauropod aerated vertebrae, in that a Qped had aerated vertebrae, while a biped had aerated ribs and ventral bones?

    (http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0003303)

  19. DD Says:

    Oh, I see you all did hear about it already!


  20. [...] from the US and England are especially pneumatic–the mean for all of them, including Sauroposeidon, ‘Angloposeidon’, some shards of excellence from the Isle of Wight, and assorted odds [...]


  21. [...] though, that some slices of Sauroposeidon (and ‘Angloposeidon’, as it turns out) have ASPs of 0.89, and thus had an in vivo density half that of the above slice (0.11 x 1.9 = 0.21 [...]


  22. [...] vertebra. The external bone surface would have been over on the left; it was either very thin (which happens) or a bit eroded, or both. The arrow is pointing at something weird–a plate of bone inside [...]


  23. [...] some dust off one of the verts with a vacuum cleaner hose, and watching in horror as some of the millimeter-thin external bone just flaked off and flew away. That was in the late 1990s, when the verts were still stored in the [...]


  24. […] this large and dense.) A figure derived from that work made it into a couple of papers and this post, and appears again […]


  25. […] There’s almost nothing but nothing there, Sauroposeidon edition […]


  26. […] There’s almost nothing but nothing there, Sauroposeidon edition […]


  27. […] visceral look at how much air there can be in the bones of birds, see this post, and this one and this one for […]


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