Brachiosaurus: both bigger and smaller than you think

March 16, 2009

I made this, just for the heck of it.

big-brachiosaurids-and-pathetic-mammals-480

The critters are, from left to right:

  • OMNH 53062, the holotype of Sauroposeidon proteles, with a reconstructed skeleton grayed in;
  • HM XV2, a fibula of Brachiosaurus brancai, which represents the largest known individual of Brachiosaurus;
  • HM SII, the nearly complete mounted composite skeleton of Brachiosaurus brancai in Berlin;
  • a 20-foot-tall, world record giraffe;
  • a 6’2″ human being, such as myself.

The vertebrae of Sauroposeidon are about a third longer than their counterparts in HM SII, but only about 15% larger in diameter. I have therefore always scaled up the body of Sauroposeidon by only 15% relative to HM SII. It may have been bigger or smaller, I’m just trying to follow what few numbers I have to go on as slavishly, and conservatively, as possible. Sauroposeidon is shown here with a more vertical neck than Brachiosaurus because that’s how I had the necks posed in the  two separate skeleton reconstructions before I decided to combine them, and I’m lazy, and that’s not the point of the post anyway.

The point of the post, or the first point anyway, is that almost everyone, everywhere, at all times underestimates the size of Brachiosaurus. This is because of the immense influence of the HM SII mounted skeleton. Practically every estimate of length or neck length or browsing height or mass or anything else for Brachiosaurus is based on that one skeleton. But we know that there were bigger individuals of Brachiosaurus roaming around, like HM XV2, which was 12-13% larger. Not only that, but we can be pretty certain that HM SII was not fully mature because the scapula and coracoid are unfused, and we know these elements are fused into a single scapulocoracoid in mature brachiosaurids. So between SII being not all grown up and XV2 being considerably bigger, we ought to think of XV2 and not SII when we think about big Brachiosaurus was.

Now, 12-13% might not seem like much, but it’s considerable. It’s the difference between me (6’2″) and someone seven feet tall. HM SII has a neck 8.5 meters long; that of XV2 would have been 9.5 meters long, which is longer than the neck of the holotype of Mamenchisaurus hochuanensis (9 m), but shorter than the estimated neck length of Mamenchisaurus sinocanadorum (~12m).

Crucially, XV2 would have massed 1.4 times as much as SII (1.125^3, because mass depends on volume, which scales with the cube of length). That holds true no matter how much you think SII weighed. If SII had a mass of 40 tons, then XV2 was 56 tons; if SII was 30 tons, XV2 was still 42 tons.

Maybe the most interesting thing about this is that, so far as we can tell, XV2 was almost exactly the same size as the holotype individual of Sauroposeidon. So anything I or anyone else has written about Sauroposeidon being bigger, absolutely, than Brachiosaurus, is bobbins. Sauroposeidon still had a considerably longer neck, 11.5 meters to XV2′s 9.5, but the cervical skeleton weighed about the same thanks to the higher air space proportion in Sauroposeidon. In fact, if the higher ASP of Sauroposeidon applied to the rest of the vertebral column, then the holotype individual of Sauroposeidon might have weighed less than XV2!

The evolutionary upshot is that, as far as we can tell, big brachiosaurids stayed about the same size from the Kimmeridgian-Tithonian (Late Jurassic) to the Aptian-Albian (Early Cretaceous). Maybe they hit some kind of limit, but I doubt it, because Argentinosaurus was probably a lot heavier and Bruhathkayosaurus and Amphicoelias would have knocked any known brachiosaurid right out of the park. I think it is more likely that the debits imposed by large body size finally caught up with the selective advantages of same, within that lineage (but not at the same point within other lineages). Whatever the reason, the biggest known brachiosaurid didn’t get any bigger than Brachiosaurus. Which puts the evolution of the longer, more pneumatic neck in Sauroposeidon into a new light. It might have been a cheat, an evolutionary hack to overcome a limit on whole-body growth, even if that limit was a ‘soft’ one imposed by balanced selection pressures in both directions. That’s sort of assuming that Sauroposeidon was just Brachiosaurus with a redesigned front end, but the weirdness we see in the vertebrae might have extended to the rest of the animal. We won’t know until someone digs up some more specimens. Sigh.

The second point of the post is that, as indicated by the title, Brachiosaurus might have been smaller than we commonly think. Since the 1980s there have been a couple of ~30 ton estimates out there for HM SII, one by Anderson et al. (1985) based on limb bone allometry and one by Paul [1988] based on volumetrics (I have to put 1988 publication dates in brackets rather than parentheses or mrrfin’ frrfin’ WordPress automatically changes the 8 and the ) to a smiley, dammit). I think that by and large people have gotten pretty comfortable with the idea that SII was a 30 ton  critter.

But it might–might–have been quite a bit lighter. Paul (1997) assigned the neck a density of 0.6 g/cm^3 and the torso a density of 0.9 g/cm^3. Those are probably too dense. Some birds have necks as un-dense (sparse?) as 0.3 g/cm^3, and that does not strike me as unreasonable for sauropod necks given the amount of pneumaticity indicated by the skeleton. The lungs and air sacs of birds can account for up to 20% of the volume of the body. Not of the torso, of the whole body. And based on my calculations for derived theropods and sauropods, up to 10% of the whole-body volume was occupied by air in the pneumatic bones. That’s 10% in addition to the 20% for the lungs and air sacs, or 30% of the whole body  volume. That would give a whole-body density of about 0.7 g/cm^3, which is in fact what has been found for some birds.

I got 0.8 g/cm^3 for the whole-body density of Diplodocus in my 2005 paper, and other authors have since used that number for other sauropodomorphs. That’s gratifying, but it’s probably wrong. I erred conservatively at every possible point in that calculation and just flat left out some known air spaces whose volume I could not reliably estimate (e.g., vertebral diverticula outside the vertebrae). I also used 10% rather than 20% for the part of the whole-body volume occupied by the lungs and air sacs, because values as low as 10% have been reported for some birds and I was being conservative. But I don’t think that bird-like densities around 0.7 g/cm^3 are unrealistic for sauropods; in fact, I’d be surprised if the really pneumatic ones–like big brachiosaurids–weren’t about that sparse.

And speaking of big brachiosaurids, Henderson (2004) used computerized volumetrics and a density of 0.8 and got a mass of 25.8 tons for HM SII. If the density was really 0.7 that would shave off an additional 10% and bring the mass down to 22.7 tons. That’s getting crazy light; it’s about half of what Bakker and Alexander were proposing for Brachiosaurus in the mid-80s. And it’s still a quarter lighter than what Anderson (1985) and Paul [1988] got.

So, for the sake of argument, let’s say that HM SII did mass only 22.7 tons. That would give XV2 a mass of 32 tons, and Sauroposeidon a mass of only 34.5 tons without taking any additional pneumaticity into account.

That seems totally nuts. But every step is defensible*, and it might even be true.

* That means if you want to tear me a new one in the comments because teh Brachiosaurus wuz 50 tons!!!1!!111!, please be sure to specify which links in the chain of inference you disagree with, and why.

References

  • Anderson, J. F., A. Hall-Martin, and D. A. Russell. 1985. Long-bone circumference and weight in mammals, birds and dinosaurs. Journal of Zoology 207:53-61.

  • Henderson, D. M. 2004. Tipsy punters: sauropod dinosaur pneumaticity, buoyancy and aquatic habits. Proceedings: Biological Sciences 271 (Supplement):S180-S183.

  • Paul, G. 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.
  • Paul, G. S. 1997. Dinosaur models: the good, the bad, and using them to estimate the mass of dinosaurs; pp. 129-154 in Wolberg, D. L., Stump, E., and Rosenberg, G. (eds.). Dinofest International: Proceedings of a Symposium Sponsored by Arizona State University. Academy of Natural Sciences, Philadelphia, 587 pp.
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58 Responses to “Brachiosaurus: both bigger and smaller than you think”

  1. Allen Hazen Says:

    About the 8 and the ) being converted to a smily face: I don’t know about the WordPress software, but I have encountered similar annoyances elsewhere. One thing that seems to work sometimes is: leave a space before the ), then type some more words, then go back and delete the space.

    As for content: working estimates of pn~ity back into the calculations for mass has been suggested before, but I’m not sure I’ve seen it done with actual numbers before: neat! (I’m not a professional, so I could easily miss the umpteen previous publications doing this calculation if there are umpteen.)
    Mind you, even 34 tons is big: given incompleteness of specimens and uncertainty about body form, ALL numbers for Paraceratherium are soft, but current thinking (am I right about this?) is that even very big ones were probably <20.

  2. David Hone Says:

    All sounds good Matt. I wonder what has inspired you to think about brachiosaur sizes of late? ;-) By the way, while in Berlin I was told of a humerus in the collections that was around 2.5 m long, and I measured that of the mount at about 2.2. Does that put it in the range of the largest? It is less than 12% bigger than the other, but then given the chimeric nature of the Berlin mount, I assume some bits are a bit big and some a bit small compared to what they should be…

  3. Mike Taylor Says:

    Hi, Dave. The Berlin mount is not _that_ chimeric — it is substantially based on a single individual, and in particular the much-admired right humerus is from that individual. Janensch (1961:187) measured it at 213 cm, so if there really is a 2.5 m humerus in the collections, then it’s a whacking 17% longer than that of SII, and so 4% longer than we’d extrapolate for XV2. Which would be awesome.

    But. Who did you hear that from? Because I am highly doubtful. For one thing, the super-detailed Janensch monograph on Tendaguru sauropod limb and girdles doesn’t mention this element; for another, I’ve not seen it in my own passes through the Humboldt Museum collections. And in all my adventures with apocryphal brachiosaur elements, I’ve not heard mention of it before. All that said — I would LOVE you to be right :-)

  4. Nathan Myers Says:

    All I’ll add is that if you want this thing to fly, you’ve got to get the weight down further.

    I’m reminded of the historical progress of estimates of the charge on the electron. The published figures crept very gradually downward from Millikan’s original measurement, always on the high side. Nobody wanted (or, perhaps, was permitted) to publish a value that was very far from his, so it took a long time to converge on the present value.

  5. Matt Wedel Says:

    Interesting you should mention that. There is a table in an upcoming sauropod paper that illustrates something very similar…I can say no more.

  6. Mike Taylor Says:

    Oh, you tease!

  7. Philip Kahn Says:

    Your illustration prompted me to stitch it all together into a nice widescreen-background sized piece:

    http://imagehost.revealedsingularity.net/sauropod_heights.png

    Teeny little mammals.

  8. David Hone Says:

    Mike, re: a giant humerus I think it was Wolf Dieter Henirich. I didn’t get to see or measure said supposed humerus, so it could be in error, misremembered (by me or him) mismeasured, reconstruted wrong, who know what, and even in the Berlin basement, that should be hard to miss. I was definately told there was a much bigger one out there, whether or not that is true is another matter!

  9. erwin Says:

    I have a lame question – how long is HM SII?
    I connot find it anywhere…

  10. Matt Wedel Says:

    We need to get to the bottom of this. A 2.5-meter humerus…whew. That would be as long as the longest-known femur of Argentinosaurus. And it would be from an animal 1.6 times as massive as HM SII. That’s a little scary.

    As a scientist, I have to say I doubt it’s true. It’s not mentioned by Janensch, and Mike and I didn’t see any sign of a humerus that big.

    But as a sauropod fan, of course I hope it’s the real deal.

  11. Matt Wedel Says:

    erwin–I have seen 74 feet mentioned for SII, but I can’t recall where. Funny, I am always worried about how tall things are, it is good to be reminded that they have other dimensions as well.

  12. Mike Taylor Says:

    Janensch (1950b) gives the “length along the neural canal” for the HMN SII mount as 22.46 m. It’s not completely clear whether that includes the skull, but the sum of the lengths given for the skull (0.77), neck (8.78), torso (3.92), sacrum (1.07) and tail (7.62) is 22.16 m, which is a good enough match for the whole-length figure that I guess it must indeed include the skull, plus a little slop.

    Those booger-heads Naish et al. (2004:793) cite a length of 25 m from Paul (1988) but don’t give a page number. At any rate, Paul (1988:table 1), which gives many measurements of several important sauropod specimens, gives 22.2 m for SII, which is Janensch’s figure rounded to the nearest 0.1 m. I wonder whether Naish et al. used Paul’s 25 m estimate for XV2; if so, that’s sneaky, as they use it as a baseline for estimating the length of “Angloposeidon”, but they’ve been comparing that animal’s cervical with those of SII. Explain yourself, Dr. Naish!

    [It's surprising that Paul's SII length estimate corresponds with Janensch's, since most of that paper consists of Paul's criticisms (justified and unjustified) of Janensch's reconstruction, but he argues that his version's shorter torso and longer tail cancel out.]

    References:

    Janensch, Werner. 1950. Die Skelettrekonstruktion von Brachiosaurus brancai. Palaeontographica (Suppl. 7) 3:97-103.

    Naish, Darren, David M. Martill, David Cooper and Kent A. Stevens. 2004. Europe’s largest dinosaur? A giant brachiosaurid cervical vertebra from the Wessex Formation (Early Cretaceous) of southern England. Cretaceous Research 25:787-795.

    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.

  13. erwin Says:

    Thank you very much! :)

    I saw 22 m in Wedel et al (2005)* and 25 (!) in english Wikipedia, so I was a lil bit confused…

    * Wedel, Mathew J.; Cifelli, Richard L. (Summer 2005). “Sauroposeidon: Oklahoma’s Native Giant” (PDF). Oklahoma Geology Notes 65 (2): 40–57.

  14. Zach Armstrong Says:

    Does anyone have a copy of Paul’s papers on the subject that they could send me if I gave you my email address?

    Thanks…

  15. Zach Miller Says:

    Hellooooo new wallpaper!

  16. Nathan Myers Says:

    I wonder if magnetite could be preserved in a sauropod skull… Picture herds of B. aligned north/south.

  17. Graham King Says:

    awe-some!

    Nathan Myers wrote:

    I wonder if magnetite could be preserved in a sauropod skull… Picture herds of B. aligned north/south.

    How about picturing all the sauropods there ever were (snatched from time at the moment of their maximum size before demise) marching in a procession, arranged in order of size… the camera swoops down from far above, you see the long snaking line of necks and tails, swaying backs and rippling muscle, sun low in the sky, individuals casting their shadows off to one side so you see their marching silhouettes, a la Fantasia… camera swoops down to eye-level then chest-level of smallest individual in line, zooms in for first close-up then tracks back along the ever-larger majestic throng… rising and drawing back to show their full awesomeness (a row of standard trees or double-decker buses or boxcars or something running parallel to give a consistent sense of scale)…

    Sigh…

  18. Richard Says:

    20 feet tall giraffe? Holy smokes! Isn’t the world record 5.87m?

  19. David Hone Says:

    I have heard of giraffes in zoos that top 20 feet. There could be a measuring issue here depengin on where people measrue to (the back or top of the head, top of the horns, when reaching) and of course the general fact that even in captivity it’s hard to measure them accurately.

  20. Matt Wedel Says:

    About the 20-foot-tall giraffe…the number is from the awesomely comprehensive Wood (1982), which I strongly urge everyone to pick up a copy of while they can still be had. The short version, probably copied from Wood, is here. Beware that the 7m “between the pegs” measurement mentioned on that page might be legit but does not represent the height of the standing animal. It is well known that big animals are taller laying down than standing up, and big game records and savvy zoologists take this into account. As usual, see Wood for a fuller discussion.

    Wood, G.L. 1982. The Guinness Book of Animals Facts & Feats. Guinness Superlatives Ltd., Enfield, Middlesex. 252 pp.

  21. Nima Says:

    Matt, I am both shocked and impressed! Every step indeed looks defensible – but something there strikes me as odd… who exactly is Henderson, and what sort of computer model did he use? (are we speaking of Douglas Henderson, the skin texture-averse pastel artist of Maiasaura fame?)

    That looks to be the main weak link in the 22 ton brachiosaurus argument. In Paul’s paper, there is a skeletal illustration for the 32 ton version of HMN SII where the flesh looks about the right amount for the skeleton to support without fat deposits. I doubt Henderson’s computer model was based on this. Did he actually publish images of that model in his paper? Visuals are critical here. The thing can’t just be skin and bone. The illustrated size of the pneumatic bones also affects the estimated amount of air inside them. For example, the skeletals I see here look far too similar to Janensch’s overly long-bodied version (yes I know you fixed the tail, but the rib cage and dorsals are still a whale).

    One of the problems I’ve seen with most weight estimates is that either no model is used (just math, as with Russell, Anderson and Alexander) or the model is never described or published (as with Colbert’s estimate). In other words, visual and structural fidelity and anatomy are apparently not important to some of these authors, and the science suffers as a result.

    Another issue is the diverticulae outside the neck verts. If they were too big, there would be no place for the neck muscles to attach. And somehow a 22 ton Brachiosaurus with big diverticulae all over its body just below the skin, seems like a very fragile creature. One bite from a predator and the air sacs would be pierced or ruptured, opening the way for simultaneously internal AND external infections that seem incapable of healing. I don’t deny that Brachiosaurs were very pneumatic, that’s evident from the bones. But with diverticulae and air sacs NOT recorded in the bones, it is very easy to be over-speculative to go too far.

  22. Mike Taylor Says:

    Hi, Nima. No, we speak not of palaeoartist Doug Henderson but of biomodelling guru Don Henderson, whose papers on this subject you really ought to read. Henderson’s work is meticulous and well documented — even when you disagree with his results, his reasons for asserting them are explicit. I certainly wouldn’t call his involvement “the main weak link in the 22 ton brachiosaurus argument”!

    For what it’s worth, I did my own GDI on Giraffatitan based on Paul’s (1988) skeletal reconstruction, and obtained a total body volume of 29171 l, corresponding to a mass of 23337 kg. I found that very difficult to believe, but couldn’t find a legitimate reason not to include it in the paper other than personal incredulity, so it’s in (and currently in press at JVP).

    I think part of the problem is that we don’t have a good handle on what a given tonnage looks like. I see the Giraffatitan skeleton in Berlin, and think, that thing has to weight more than 23 tonnes. But that conviction is largely based on the idea that elephants weight six or seven tonnes, whereas in fact most of the elephants we see in zoos mass closer to two or three tonnes. To put it another way, it may simply be that we’re underestimating what a huge thing a 23-tonne animal is.

    By the way, Colbert’s (very fat) model was published; you can go and buy an exact duplicate yourself on eBay and replicate his experiment, if you want — he used a commercial toy.

    Matt Wedel and Daniela Schwarz-Wings have (separately) done a lot of well-founded (i.e. not speculative) work on cervical diverticula. They’re not just blowing smoke. In fact, I am if anything inclined to think that both Matt and Daniela restore too much neck muscle — much less than Greg Paul, anyway.

  23. Matt Wedel Says:

    In Paul’s paper, there is a skeletal illustration for the 32 ton version of HMN SII where the flesh looks about the right amount for the skeleton to support without fat deposits. I doubt Henderson’s computer model was based on this. Did he actually publish images of that model in his paper? Visuals are critical here.

    To follow up on what Mike wrote: Don Henderson did base his digital model on Paul’s skeletal reconstruction, and he has published images of the model in multiple views, which makes it even better documented than Paul’s work. (Paul published the drawing but no photos the half-model based on the drawing that he used for the actual volumetric measurement).

    Another issue is the diverticulae outside the neck verts. If they were too big, there would be no place for the neck muscles to attach.

    I had no good way of estimating their dimensions, so I didn’t include them in my 2005 paper, which is one of the reasons the 0.8 g/cm^3 I got in that paper is probably too high.

    And somehow a 22 ton Brachiosaurus with big diverticulae all over its body just below the skin, seems like a very fragile creature.

    Pelicans have extensive subcutaneous diverticula, like bubble wrap between the skin and the muscles, and extremely light bones, with ASPs up in the Sauroposeidon/pterosaur range. And yet they lead boisterous lives, diving into the water from great heights to catch fish, eating pigeons, and biting tourists on the head.

    Mike made the good point that none of us has a good intuitive sense of what a 10- or 20-ton animal looks like. Someone who did have a good gut level impression of how big a 10-ton elephant ought to be might still be terrible at estimating the masses of sauropods, if sauropods really were as sparse as 0.7 g/cm^3. I would further submit that most of us have no idea how light big birds really are, with the exception of ratite ranchers, falconers, and zookeepers. So going with “what seems reasonable” is a poor guide here.

    The illustrated size of the pneumatic bones also affects the estimated amount of air inside them. For example, the skeletals I see here look far too similar to Janensch’s overly long-bodied version (yes I know you fixed the tail, but the rib cage and dorsals are still a whale).

    The dorsal column might be too long, but the vertebrae are not drawn any taller than they actually are (and of course width cannot be assessed in a lateral view reconstruction). Shortening the torso would actually increase the proportion of air in the entire animal as estimated from the vertebrae. I’ll explain that.

    Let’s say that at an any given transverse slice through the torso, the dorsal vertebra makes up 10% of the cross-sectional area, so the dorsal column makes up 10% of the volume of the torso. If we shorten the torso, that’s just throwing out slices; the vertebral column is still 10% of the torso pie, it’s just that the pie has gotten smaller. But as the torso gets shorter the neck gets to be a bigger proportion of the total body volume. And the neck is probably between 40% and 70% air, based on real published data from real birds. So basically shrinking the torso actually decreases the density of the reconstructed animal, because the torso was denser than average to start with.

  24. William Miller Says:

    If sauropods had such low densities, they would have floated quite easily. Could a sauropod propel itself through the water by kicking? Elephants can swim fairly well, and they have big blocky round feet too.

    I’m not claiming the old ‘aquatic sauropod’ junk, but it occurs to me that sauropods could have crossed ocean straits, huge Amazon-like rivers, or large lakes this way. A sauropod was big enough that it could probably be OK without eating while swimming something the size of the English Channel…

    Could sauropods have reached near-shore islands in this way?

  25. Nathan Myers Says:

    What, with all those pliosaurs zooming around? Good luck.

  26. erwin Says:

    Hi,
    I have another question. Is it POSSIBLE that Sauroposeidon weight much more – even 60 tonnes?
    My reasons:
    1) Matt Wedel and Richard Richard wrote in 2005 (page 52):
    “Whereas Brachiosaurus is estimated to have weighed 30 metric tons, Sauroposeidon may have tipped the scales at 50 tons.”
    So, Sauroposeidon is 1,(6) times more massive. When we put a different mass estimation for Brachiosaurus – e.g. 38 tonnes obtained in Gunga et al. (2008) – we can estimate mass of Sauroposeidon as ca. 63 tonnes.

    2) Matt Wedel and Richard Richard wrote in 2005 (page 52):
    “Despite their great length, the vertebrae of Sauroposeidon are only slightly larger in diameter than those of Brachiosaurus, and we estimate that its body was only 10% to 15% larger than that of its Jurassic cousin.”
    So, if we assume that Sauroposeidon can be 15% bigger than Brachiosaurus, it’s mass will be 1,52 times bigger. When we take Brachiosaurus’s mass from Gunga et al., we can calculate Sauroposeidon’s mass as 58 tonnes.

    Do you think my reasons are good? Of course i demonstrated maximum mass of Sauroposeidon a nd it can weight much less.

    References:

    Wedel, Mathew J.; Cifelli, Richard L. (Summer 2005). “Sauroposeidon: Oklahoma’s Native Giant” (PDF). Oklahoma Geology Notes 65 (2): 40–57.

    Gunga, H.-C., Suthau, T., Bellmann, A., Stoinski, S., Friedrich, A., Trippel, T., Kirsch, K., and Hellwich, O. 2008. A new body mass estimation of Brachiosaurus brancai Janensch, 1914 mounted and exhibited at the Museum of Natural History (Berlin, Germany). Fossil Record 11(1):28-33. doi: 10.1002/mmng.200700011.

  27. erwin Says:

    PS Of course there should be Richard Cifelli, not Richard Richard… My apologises…

  28. Mike Taylor Says:

    Hi, Erwin. Yes, I think it is POSSIBLE that Sauroposeidon reached 60 tonnes, at least when healthy and fat. Remember that ALL we have from that animal is a sequence of three-and-a-bit cervicals. Matt and his buddies had to use a lot of guesswork about the torso (as they make clear in the paper), and as the torso accounts for 70% of the body volume in Giraffatitan, reconstructing it differently could have a big effect.

    But I would not put too much trust in the Gunga et al. estimate: even though they use a new “slim” version of their computer model, it is still pretty darned fat — literally twice the body volume that I got from using GDI on Greg Paul’s (1988) multiview restoration (Taylor in press.)

    (Not that I am 100% convinced about my own estimate either!)

  29. Mike Taylor Says:

    (Erwin: 50 tonnes was a typo in my comment, I meant 60 tonnes. I’ve now fixed that, and deleted your comment where you pointed it out.)


  30. [...] large titanosaurs would be  invaluable for those of us who are interested in body proportions, neck elongation, mass estimation, and all that good stuff. But sadly the second paper contains no table and almost [...]

  31. William Miller Says:

    Kind of a late comment, but one question: would a Sauroposeidon-size neck with a density of only 0.3 g/cm^3 still be able to support its weight and that of a head? I always thought the bones would be surrounded by enormous muscles… is that wrong?

  32. Matt Wedel Says:

    Good questions. AFAIK, no one knows the answers. On the one hand, you ask if such a sparse neck could support itself. On the other hand, I would ask if a denser neck could support itself. If the neck of a brachiosaurid was built like that of a giraffe, it would be 3x heavier than if it was built like that of a goose. The lighter the cervical vertebrae are, the less muscle mass you need to support them, and the less muscle mass you need to support that muscle mass, and so on. Any model that examined the effects of pneumatization on neck support would need to work through things iteratively to take those sorts of things into account.

    For a while I entertained the idea that you could estimate the neck muscle volume by looking at the surface area of the vertebrae available for muscle insertion, but now I’m pretty sure that would be a waste of time. More than one muscle can insert on a common tendon–this happens in bird necks, and it happens in your calves (gastrocnemius and soleus muscles insert via Achilles tendon). I think that means that measuring insertion area is only going to give a VERY broad estimate of muscle volume or cross-section, probably with uncertainty of 2-3x at best. I can do that well just interpolating between giraffes and geese, and save myself a lot of math.

    If anyone has a solution, please publish it!

  33. Matt Says:

    One thing I’m always intriqued about with sauropods are the way the necks are now reconstructed. I agree with Stevens and Parrish reconstructions on the neck posture of Apatosaurus and Diplodocus. However think they are wrong on how Brachiosaurs held their necks.
    The front part of Brachiosaur body morphology is just the opposite of diplodocids. Brachiosaurs have long front front legs and short back legs. The only modern analog is indeed the Giraffe. So I would have to agree with Greg Paul that Brachiosaurs would be high browsers, where Diplodocids would be low to mid level feeders. What is your position on this idea?

  34. Mike Taylor Says:

    Hi, Matt. I wish, I wish, I reall wish I could give your question an answer in the detail it deserves. But you wouldn’t want me to steal the thunder from our forthcoming paper, would you? I’ll give you a hint, though: we agree with you about brachiosaurs.

    :-)

  35. Matt Says:

    Hi Mike,

  36. Matt Says:

    Hi Mike, sorry about the last post.I Hit the wrong button. I meant to say thanks for the reply, and I look foward to reading the paper. Sauropods are very intersting animals, and brachiosurs in particular are fascinating in both functional morphology and systematics.

  37. William Miller Says:

    Yeah, would be interesting to know…

    I know hollow bones can be very strong – I’m just thinking that as small as they were relative to the bodies, brachiosaur heads were still pretty big, and the neck would have to have enough muscles to move it. Maybe the air sacs were smaller in sauropods than birds – would there be any way to test that?

  38. Matt Wedel Says:

    brachiosaur heads were still pretty big

    True dat.

    Maybe the air sacs were smaller in sauropods than birds – would there be any way to test that?

    Depends on whether you mean the respiratory air sacs in the torso, or their diverticula in the neck. From what I’ve seen, the neck vertebrae of Brachiosaurus were almost totally jacketed in diverticula, with only the apophyses and some of the laminae sticking out for muscle and ligament attachment. Bird cervicals usually have diverticula around them but not to the extent that I have seen in sauropods. So based on the osteological evidence, I think sauropod necks were at least as pneumatic as those of birds, and maybe more so.

    For the thoracoabdominal air sacs, who knows? Many authors have assumed that the air sacs of non-avian dinosaurs must have been less extensive than those of birds, but this is really just a guess about the presumed pace of evolution and when the author thinks the air sac system evolved. Given the persuasive evidence for respiratory air sacs in pterosaurs and saurischians, I’m guessing it’s pretty darn old.

  39. William Miller Says:

    OK, thanks. That’s interesting.

    It’s also kind of odd: in birds, the air sacs are obviously useful for flight, and they might have been useful for weight lightening in sauropods: but the common ancestor would have been flightless and too small to need the lightening. So what drove their evolution in the first place, I wonder?

  40. Matt Wedel Says:

    William, that is such a good question that I’m going to answer it in a separate post. I started writing it as a comment but it’s definitely post-worthy. Stand by.

  41. William Miller Says:

    Thank you very, very much!


  42. [...] it, William Miller has been asking some great questions over in the comment thread for “Brachiosaurus: both bigger and smaller than you think“. Here’s his most recent, which is so good that the answer required a post of its own: [...]


  43. [...] This post on the wonderfully nichey Sauropod Vertebra of the Week Blog has an interesting story about size in Brachiosaurs.  What it underlines is the influence the mounted skeleton of Brachiosaurus brancai in the [...]


  44. [...] These numbers are like pieces of legislation, or sausages: the results are more pleasant to contemplate than the process that produced them. They’re ugly, and possibly wrong. But they give us someplace to start from in considering the possible sizes of the biggest sauropod trackmakers. Something with a hindfoot track 1.5 meters wide would be, using these numbers, conservatively more than twice as big as (2.11x) the mounted Carnegie Diplodocus or 170% the size of the mounted Berlin Giraffatitan. That’s right into Amphicoelias fragillimus/Bruhathkayosaurus territory. The diplo-Diplodocus would have been 150 feet long, and even assuming a very conservative 10 tons for Vanilla Dippy (14,000L x 0.7 kg/L = 9800 kg), would have had a mass of 94 metric tons (104 short tons). The monster Giraffatitan-like critter would have been “only” 130 feet long, but with a 14.5 meter neck and a mass of 113 metric tons (125 short tons; starting from a conservative 23 metric tons for HM SII). [...]

  45. William Miller Says:

    The vertebrae of Sauroposeidon are about a third longer than their counterparts in HM SII, but only about 15% larger in diameter.

    If Sauroposeidon was 33% bigger linearly rather than 15%, it would weigh more than 50 tons, right? (1.33 cubed x 22.7 = 53.4). Is there something about Sauroposeidon’s vertebrae that suggests the diameter is a better guide than the length to the animal’s total size? To my admittedly unskilled first glance, it doesn’t seem obvious why one would be more accurate than the other.

  46. Matt Wedel Says:

    Is there something about Sauroposeidon’s vertebrae that suggests the diameter is a better guide than the length to the animal’s total size?

    I thought, and still think, that diameter is probably a better guide to size because neck length can change a lot without changing the size of the animal. Barosaurus is about the same size as Diplodocuss, only with a longer neck. There are lots of examples of this sort of thing both within and outside of sauropods.

    On the other hand, diameter is almost certainly directly related to the “bigness” of the body, which is the driving factor in mass estimation.

    Obviously this is only true for cervicals; if all we had were isolated dorsals, the length difference would be crucial because it would mean the body was longer and therefore heavier, just as Mike found for Brachiosaurus vs Giraffatitan in his new paper.

    To take just one of many possible examples, the dorsal vertebrae of Mamenchisaurus are no longer, proportionally, than those of other basal eusauropods. If we found a wicked long cervical, say from Mamenchisaurus youngi, and extrapolated a wicked big animal, we’d be way off. We’d be much closer if we noted the modest diameter of the cervical and reconstructed a similarly modest body.

    In sum, I can’t think of any reason why cervical length would be a good indicator of body size. I admit that diameter might be an imprecise, but I can’t see how it could be less accurate than length.

  47. William Miller Says:

    Oh, OK, that makes sense … I probably should have known that.


  48. [...] to those of birds, 0.75 or even 0.7 is not beyond the bounds of possibility (as discussed here and also covered by Zach in his [...]


  49. [...] Now, scroll back up to the diagram of the giant moa, which had a mass of 257.5 kg “assuming a specific gravity of 1″. If the moa was as light as an extant bird–and its skeleton is highly pneumatic–then it might have had a mass of only 188 kg (257.5*0.73). Or perhaps its density was higher, like that of a lizard or a croc. Without a living moa to play with, we may never know. Two points here: first, the common assumption of whole-body densities of 1.0 is demonstrably incorrect* for many animals, and second, since it’s hard to be certain about the densities of extinct animals, maybe the best thing is to try the calculation with several densities and see what results we get. (My thoughts on the plausible densities of sauropods are here.) [...]


  50. [...] by sauropod representations, both 2D and 3D, including those made by others and a few that I have generated myself. How could I possibly be surprised [...]


  51. [...] they’re Vanessa-sized or smaller; the big ones are taller than I am…and they’re still from subadults. Must blog sometime about the awesomeness of the basement full o’ sauropods at the MfN, but [...]


  52. [...] The mounted Giraffatitan is a pretty damn big animal by anyone’s standards, but it’s demonstrably smaller than another individual from Tendaguru, and the scap-coracoid joint is unfused. On the other hand, [...]


  53. [...] (although B.a. had a longer torso). But we know that brachiosaurids got bigger, as evidenced by the XV2 specimen of Giraffatitan, and based on the lack of scapulocoracoid fusion in both FMNH P25107 and the mounted Giraffatitan. [...]


  54. [...] Dinosaurusten toisessa suuressa päälinjassa, liskonlantioisissa, johon linnutkin kuuluvat ilmapussien merkitys on vielä suurempi. Lintujen luutkin ovat täynnä ilmapussien onkaloita, samoin olivat petodinosaurusten ja jättimäisten sauropodien luut. Ilma tekee eläimistä kevyitä. Lintujen on hyvä lentää ilmatäytteisillä luilla ja sauropodit olivat kokoonsa nähden yllättävän kevyitä. [...]


  55. […] result has cast a long shadow over discussions of sauropod masses, as in this paper and these posts, so it’s nice to see similar results from an independent analysis.  If you’re curious, […]

  56. djlivus Says:

    Brachiosaurids are by far the most beautiful dinosaurs. Too bad that Sauroposeidon may not be a brachiosaurid. Any news about Brachiosarur Nougaredi?

  57. Mike Taylor Says:

    Nothing much on “B.” nougaredi, beyond what’s in the recent Mannion et al. paper. (We really must blog about that.)


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