Xenoposeidon week, day 4: the question everyone is asking … how big was it?

November 18, 2007

[Sorry about the late posting today: I had to leave the house at 7:15 to fly to Copenhagen for Christmas lunch — long story — and I am completing today’s post from my hotel room.]

There’s no getting away from it: everyone wants to know how big dinosaurs are. Xenoposeidon is based on a single partial vertebra, so there is no way to be at all sure about the size and shape of the whole animal; but we knew that everyone would want to know, so in the paper (Taylor and Naish 2007, natch) we made the best guesses we could. Details on how we did this follow below.

Then, a few months after the revised manuscript was accepted by Palaeontology, purely as a joke, I put together what I called “the first scientifically rigorous skeletal reconstruction of Xenoposeidon“. The joke is based on a very well-established style for skeletal reconstructions of complete or nearly complete skeletons, first popularised by Greg Paul, in which the animal is shown in left lateral view, with bones drawn in white and the soft tissue outlined as a black silhouette — as in these rather beautiful Morrison Formation diplodocids from Paul (1998: fig. 1b).  F is Diplodocus carnegii CM 84 with skull CM 3542 scaled to fit, G is Barosaurus lentus AMNH 6341 (with a fair bit of guesswork to fill in the gaps) and E is Apatosaurus louisae CM 3018 with skull CM 11162 scaled to fit:

paul1998-fig1b-diplodocids-500px.jpeg

I thought it would be funny to do this for an animal known only from a single bone, showing the bone floating in the middle of a big black silhouette. Har har. (You may not find that funny. The key point here is that Matt and Darren both did, which is all I was aiming for. And it turns out that John Hutchinson agrees, which proves it.)

xenoposeidon-skeleton-500px.jpeg

In fact the only things that are remotely scientific about this “reconstruction” are that the bone is in roughly the right place (i.e. a posterior dorsal) and the human is about the right size. The actual shape of the “reconstruction” is a total guess: given that Xenoposeidon could belong in any part of the huge clade Neosauropoda, the only reason I went with a brachiosaurid body-shape rather than, say, a diplodocid was that I like brachiosaurus more. They’re just cooler. (This is how science is done, kids! Don’t tell your parents!)

It wasn’t until much later, when the publicity was in full swing, that it occurred to me that if the media were going to use the “skeletal reconstruction” it would be better to give them one with all the bones, greyed out. I made this almost as soon as it had occurred to me, and made it available to newspapers and TV stations, but it was a bit too late in the day — hardly any of them used it. Here it is, anyway:

xenoposeidon-skeleton2-500px.jpeg

Now that all the bones are back in place, it’s easy to recognise this as a knock-off of Matt Wedel’s Brachiosaurus reconstruction, as discussed in a much-overlooked Prehistoric Times article and which has since cropped up in various places. If I’d had my wits about me, I’d have credited Matt for the original “reconstruction” that went out to newspapers, but since it was only done as a joke it didn’t occur to me. Sorry, Matt!

So how did we figure out the probable size of Xenoposeidon? Since we had only one vertebra to go on, and since even that was missing the neural spine and other processes, all we had to work with were the centrum measurements. We reconstructed the centrum to be 20 cm long, with a cotyle diameter of 16.5 cm (the average of 16 cm width and 17 cm height). Then we compared that with the dimensions of vertebrae from the same position in the dorsal column of other sauropods. For this, we chose Brachiosaurus brancai and Diplodocus carnegii, because they are both known from nearly complete skeletons, and pretty much bracket the range of neosauropod body shapes.

Guessing length is easy: we just assume that the total length of Xenoposeidon would be in the same proportion to the length of one of its posterior dorsals as in the comparison taxa. The Xenoposeidon dorsal is 60% as long as the 33 cm D7 (seventh dorsal) of the Brachiosaurus brancai type specimen HMN SII (Janensch 1950: 44). If Xeno were built like a brachiosaurid, then it would be 60 per cent as long as HMN SII, yielding a length of 15 m based on Paul’s (1988) estimate of 25 m for that specimen. Similarly, the Xenoposeidon dorsal is 74% as long as the 27 cm vertebrae in the Diplodocus carnegii type specimen CM 84 (the average of the lengths of D7 and D8 as stated in Hatcher 1901:38). Therefore, a Diplodocus-like Xenoposeidon would be about 20 m long, based on the widely quoted figure of 27 m for CM 84.

But these figures are subject to a fair degree of uncertainty, and shouldn’t be taken too seriously. Suppose for example that we compared instead with D9 of Diplodocus, which is 29 cm long: the corresponding length estimate for Xenoposeidon would have been reduced to 20/29 of 27 m, which is 18.5 m.

And now to the much more handwavy problem of estimating mass. We can roughly extrapolate the mass of an animal as being proportional to the centrum volume, which in turn is proportional to centrum length times the square of its average cotyle diameter, and this is what we did in the paper. For Brachiosaurus brancai, this means that we estimate Xenoposeidon mass as (20 x 16.5 x 16.5) / (33 x 27 x 27) = 22% the mass of Brachiosaurus brancai; or as (20 x 16.5 x 16.5) / (27 x 29.5 x 29.5) = 23% the mass of Diplodocus carnegii, depending on which it most resembled.

But weight just a moment! (Har har.) What actually is the mass of Brachiosaurus brancai? An astonishingly wide range of figures have been calculated, all based on the same specimen (HMN SII). In chronological order (and do let me know if I’ve missed any):

  • 78 tonnes (Colbert 1962), based on the volume of sand displaced by a scaled plastic model
  • 15 tonnes (Russell et al. 1980) based on the dimensions of limb-bones, plotted on a best straight line through limb-bone-thickness vs. mass for extant animals
  • 47 tonnes (Alexander 1985), based on the volume of water displayed by a different model from the one that Colbert used
  • 29 tonnes (Anderson et al. 1985), using a similar though slightly more rigorous method than that of Russell et al. (1980)
  • 32 tonnes (Paul 1988), using, I think, graphic double integration or something similar (the paper is not very explicit)
  • 74 tonnes (Gunga et al. 1995), based on a computer model built using data scanned with lasers — very high-tech!
  • 37 tonnes (Christiansen 1997) by suspension of scale models
  • 26 tonnes (Henderson 2004) by measurement of computer model built by hand

We ignored the Russell et al. (1980) and Anderson et al. (1985) estimates because they are not actual measurements of anything, and depend instead on additional assumptions about scaling. We ignored the Colbert (1962) estimate, too, as it was based on a grotesquely overweight model. Worse still is the Gunga et al. (1995) estimate, which starts with ultra-precise measurements of the skeleton and then throws it away by fleshing that skeleton out in a computer model composed entirely of circular conic sections. Needless to say this makes the neck, torso and tail all hugely too wide, and the resulting volume estimate is near worthless. When they redo this work using elliptical conic sections, I will be interested to see how much their result comes down by. That leaves the more reliable estimates of Alexander, Paul, Christiansen and Henderson, and the average of their estimates 35322 kg — which seems correct using the well-it’s-way-bigger-than-an-elephant-anyway method. Using that figure (as we did in the paper), we got a probable mass of 7600 kg for Xenoposeidon — and this is course is the source of the statement, much quoted in the media, that it was “about as big as an elephant”. A big elephant.

But remember how vague this is: the lightest of the published estimates of Brachiosaurus brancai mass is 42% of the value we used, and the heaviest is 2.2 times as great. If we’d used these values in extrapolating the mass of Xenoposeidon we could have arrived at 3200 kg or 16720 kg!

For Diplodocus carnegii, we just used the estimate of Wedel 2005, 12 tonnes, and got a mass of 2800 kg for Xenoposeidon. There is rather less divergence in the various published mass estimates for this animal; but whether that’s because people’s work on it is more consistent, or just because not so many people can be bothered estimating the mass of so relatively uncharismatic a sauropod, I wouldn’t like to say.

All this means that Xenoposeidon was small — for a sauropod. In our poxy extant ecosystems, elephants are considered tolerably large, but in the Mesozoic they would hardly have raised an eyebrow, and neither would Xenoposeidon. Why the small size? Is it a juvenile? Apparently not: in archosaurs (that is, crocodiles, birds and all descendents of their most recent common ancestor, including dinosaurs), the neural arches fuse to their centra only some way into growth (Brochu 1996), so a vertebra such as that of Xenoposeidon in which the arch is fully fused and the sutures completely obliterated indicates that the animals was mostly or fully grown. Just small. Like Paul Simon. That’s nothing to be ashamed of.

Coming up next on SV-POW!’s Xenoposeidon week: on day 5, Darren will talk about the joys and hazards of dealing with the media. Stay tuned. (And, folks, please do make the occasional comment. Just so we know someone’s listening.)

References

  • Alexander, R. McNeill. 1985. Mechanics of posture and gait of some large dinosaurs: Zoological Journal of the Linnean Society 83: 1-25
  • Anderson, J. F., A. Hall-Martin and Dale A. Russell. 1985. Long-bone circumference and weight in mammals, birds and dinosaurs. Journal of Zoology 207: 53-61
  • Brochu, Christopher A. 1996. Closure of neurocentral sutures during crocodilian ontogeny: implications for maturity assessment in fossil archosaurs. Journal of Vertebrate Paleontology 16: 49-62.
  • Christiansen, Per. 1997. Locomotion in sauropod dinosaurs. Gaia 14: 45-75
  • Colbert, Edwin H. 1962. The weights of dinosaurs. American Museum Novitates, 2076: 1-16
  • Gunga, Hans-Christian, K. A. Kirsch, F. Baartz, L. Röcker, Wolf-Dieter Heinrich, W. Lisowski, A. Wiedemann and J. Albertz. 1995. New Data on the Dimensions of Brachiosaurus brancai and Their Physiological Implications. Naturwissenschaften 82: 190-192
  • Hatcher, Jonathan B. 1901. Diplodocus (Marsh): its osteology, taxonomy and probable habits, with a restoration of the skeleton. Memoirs of the Carnegie Museum, 1: 1-63 and plates I-XIII
  • Henderson, Donald M. 2004. Tipsy punters: sauropod dinosaur pneumaticity, bouyancy and aquatic habits. Proceedings of the Royal Society of London, B (Supplement) 271: S180-S183. doi 10.10998/rsbl.2003.01.36
  • Janensch, Werner. 1950. Die Wirbelsaule von Brachiosaurus brancai. Palaeontographica (Suppl. 7) 3: 27-93
  • 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
  • Paul, Gregory S. 1998. Terramegathermy and Cope’s Rule in the land of titans. Modern Geology 23: 179-217
  • Russell, Dale, Pierre Béland and John S. McIntosh. 1980. Paleoecology of the dinosaurs of Tendaguru (Tanzania). Memoires de la Societe Geologique de France 139: 169-175
  • Taylor, Michael P., and Darren Naish. 2007. An unusual new neosauropod dinosaur from the Lower Cretaceous Hastings Beds Group of East Sussex, England. Palaeontology 50 (6): 1547-1564. doi: 10.1111/j.1475-4983.2007.00728.x
  • Wedel, Mathew J. 2005. Postcranial skeletal pneumaticity in sauropods and its implications for mass estimates. pp. 201-228 in: Jeffrey A. Wilson and Kristina Curry-Rogers (eds.), The Sauropods: Evolution and Paleobiology. University of California Press, Berkeley
Advertisements

28 Responses to “Xenoposeidon week, day 4: the question everyone is asking … how big was it?”

  1. Matt Wedel Says:

    If I’d had my wits about me, I’d have credited Matt for the original “reconstruction” that went out to newspapers, but since it was only done as a joke it didn’t occur to me. Sorry, Matt!

    Well, credit is important, even especially in this open-source world. Still, I forgive you. As Xenoposeidon‘s uncle, I was just happy to see my little meme image out there replicating.

  2. Darren Naish Says:

    One thing we must not mention here on SV-POW! is the word meme. I’ll say no more for risk of shaming my fellow bloggers.

  3. Darren Naish Says:

    By the way, awesome post Mike. What the hell is a Paul Simon?

  4. Sarah Says:

    Reconstructing the one bone in a big silhouette IS hilarious. It is secretly something I’ve wanted to see for a while.

  5. Allen Hazen Says:

    I remember the Alexander estimates from when the article came out… or at least I think I do. Didn’t he use models from the series of plastic critters the BMNH gift shop had commissioned (and which various of my younger friends and relatives got as Christmas presents)?

    I suspect the basic technological limitations of plastic model-making would lead to overestimates of mass: delicate parts have to be cast at larger-than-scale diameters for strength, and narrow gaps (say between the proximal part of a limb and the body) get filled.

    (But this is mainly to let you know that someone is listening: I think this series is great!)

  6. Mike from Ottawa Says:

    To what extent does the pneumaticity of sauropods get taken into account in doing weight estimates?

  7. Nathan Myers Says:

    The only mass estimate I would trust would come from measuring the cross-sectional areas at maximally-stressed points in each of front and rear leg bones of the same creature, and scaling according to what is known of bone strength and loading in modern creatures. I.e., compare to an elephant’s bones, and adjust according to relative strength per square unit of elephant bone vs. ostriches, storks, and alligators.

    Surely this has been done… hasn’t it?

  8. Mike Taylor Says:

    Nathan, that is essentially what Anderson et al. did, although IIRC they used femur and humerus circumference rather than CSA … weird but I think true.

    Why would you trust such an estimate more than one based on the whole animal? An estimate based on leg-bone strength is only good on the assumption that all animals are equally athletic and have equal safety factors, which not only seems like a wild leap to me but is also begging the question. Studies of extant animals show that they have significantly different SI (strength indicator), and a priori I’d expect a lower value still for big sauropods. Why would an animal the size of Brachiosaurus even need to be atheletic? It wouldn’t do a lot of running away.

  9. Mike Taylor Says:

    Mike from Ottawa,

    Matt emailed me about your comment, with the pathtically self-piteous subject line “I’m busy” and commented:

    …so I’m going to let one of you answer this one. AFAIK, the only ones who have taken pneumaticity into account are Greg Paul (by modulating specific gravities of body segments, apparently by sheer guesswork), moi in 2005, and the recent Gunga paper on Plateosaurus. Anyway, I leave it in your hands (mainly because I’ve got a ton a grading to do, and I’m still pooped from the 3 or 4 dissertations’ worth of comments I’ve written on Tutorial 3).

    What a loser. He doesn’t know the meaning of the word busy.

  10. Leslie from Glasgow Says:

    Just a note of appreciation from a newcomer. Despite being biologically disabled by a medical training [nearly ejected from orthopaedics], your reports grip me completely.
    I am full of admiration for your step-by-step caution and and your great clarity.
    I thank you.

  11. Randy Says:

    I think the only decent thing to do when discussing ontogeny and neurocentral sutures would have been to cite Irmis 2007 [JVP 27(2)]! ;)

    Seriously, using neurocentral sutures as a proxy for ontogeny in taxa other than pseudosuchians are pretty problematic.

  12. Nathan Myers Says:

    I understand that there are plenty of ways to confound mass estimates based on bone cross section measurements. Still, it starts with something directly observable. Nobody can offer a defensible guess as to how much flesh these creatures had on, or its density. Considering that a broken leg would amount to a death sentence, I can’t imagine their safety margin would be too different from that of their more active peers.

    Still, the only way to have confidence in the method would be for somebody to have done a great deal of work, analyzing many samples, and comparing to many different modern species, to develop trends and determine actually observed safety factors and how they vary with size. Given that work, though, you wouldn’t be guessing any more. Anderson’s title seems to suggest they did at least some of that work.

    Measuring circumference instead of cross-sectional area makes perfect sense if you’re looking at hollow bird bones that only have, practically, a circumference, but even there you should also be measuring wall thickness, which gives you a cross-sectional area. In bones that aren’t hollow, most of the force is conducted at and near the surface anyway. You should be able to compute an “equivalent thickness” as if they really were hollow, but you can see it getting less rigorous.

    Still, Anderson’s estimates are starting to seem better to me. I would like to see an engineer — ideally, a roboticist! — involved in the investigation.

    The reason I feel confidence in this approach is that bones continuously adjust to the stresses they experience. They are a true snapshot of the mass they supported at the time of death.

  13. Mike Taylor Says:

    Dammit all, Irmis, will you please stop superseding all the papers we cite? How the heck is a guy supposed to get any work done around here?

    Seriously, I actually didn’t know about that paper; and of course we have the rock-solid excuse that it wasn’t even published at the time we submitted Xeno. (And none of the four reviewers or two editors pointed us to it, which while not exactly an excuse is at least an indication that Darren and I are not the only lame-ors around here.)

    Regarding the ontogenetic stage of the Xenoposeidon type specimen: what we should have said, but didn’t, is that the form of the pneumatic fossa and foramen also indicate maturity, as (Matt will correct me if I get this wrong) baby sauropods have broad, shallow fossae without distinct lips and without deep foramina, whereas the fossa of Xeno has a very distinct and defined dorsal margin, a lip really, and a deep foramen contained within it. So I am confident of our result even if the reasoning behind it was not so rock solid as it appeared at the time.

    … And now I have to read your paper.

  14. Mike Taylor Says:

    Nathan,

    It is a fact — yes, verified by detailed study — that different extant animals have SIGNIFICANTLY different strength indicators (i.e. different levels of athleticism). You simply cannot say, from a bone’s ability to bear a certain amount of stress, how much it would actually be asked to bear in life. So by their very nature, Anderson et al.’s estimates are just that: estimates. I am away from my library at the moment so I can’t check this, but I am pretty sure that they make this point themselves.

    Regarding their use of circumference rather than CSA: AFAIK they didn’t try to justify this, and I still find it … very weird. I may be missing something, but it looks Just Plain Wrong. It’s a linear measurement, and what resists bending/breakage is an area measurement. If they had used the square of the circumference and regressed against that, I’d have been more inclined to trust their results. (I keep meaning to go back and redo their work using squared circumferences, but this is looking more and more like one of those little projects that I will never do.)

    By the way, I’d just to say a big thank you to everyone who’s made kind comments about this blog. We appreciated it.

  15. Nathan Myers Says:

    One expects ostriches and cheetahs to have a much larger bone-strength safety factor than elephants or hippos. What’s interesting is how the safety factor trends with body size. The square-cube law means a big animal simply cannot afford the safety factor found in a smaller animal, so it must be correspondingly less “athletic”. “Athletic” cannot mean typical activity, but peak stress; bone must adapt to the greatest stress experienced over a long period, regardless of how much time the animal may spend wallowing the rest of the time. The good news is that the bigger the animal is, the less variation it can afford; it must restrict its activity to what the bones it can afford to grow can withstand.

    The useful measurement, then, would be if the number varies much among similarly large animals, e.g. hippo, rhino, immature elephant; and how it varies among individuals of different size within a species or between similar species (e.g. african vs. indian elephant). It’s easy to get wrong and a lot of work to get right, but it stands a chance of giving a defensible answer.

    Crushing strength along the bone’s long axis depends on cross-sectional area of actual bone mass, but (1) the middle of the bone isn’t solid, it’s spongy, so area near the center isn’t the same as area near the surface; and (2) strength under other stresses than crushing may be the limiting factor. Under bending moments, the material at the center is hardly stressed at all, while the surface on one side is compressed and the other is in tension. (I.e. the middle is spongy for good reason.)

    Hence, I think regression against raw area would yield little unless you were very picky about which bits of which bones you measured. Otherwise you would need to include a measure of how the density varies from surface to center. I don’t know how much information can be extracted about the density of a sauropod tibia; is it just undifferentiated rock, or might the marrow be replaced by one mineral and the apatite crystals remain, or be replaced by another? It may be that certain bones, or parts of bones, are not subject to bending moments, but their cross section must be minimized, so they are solid. Those that *also* bear the full weight of the animal might be the best candidates for comparison, particularly if density is hard to measure.

  16. Mike Taylor Says:

    Lots and lots to get into here, so I will be brief.

    First, yes, of course, it’s not surprise that cheetah SIs vary from those of elephants. It would be great to see a study that surveys SIs across a broad range of extant taxa: does anyone know of such a study?

    Second: I very much doubt that longitudinal crushing would ever be the failure mode of any bone in an extant animal; and, yes, the far greater effect of bending forces is why nearly all long bones are able to have cavities, whether containing marrow or air.

    Third: so you may be right that regression against raw area would not give the best fit. But I don’t see how circumference can possibly be better. What we’d expect to measure as a “good at resisting bending” value would be something like the distance of the edge from the center times the thickness of the edge … which is a linear x linear measurement, which in turn is proportional, more or less, to area. So actual CSA would probably be a better proxy for this than circumference … which is where we came in.

    Fourth: rather than messing about with all this speculation, what someone should do take a whole shedload of measurements of extant animal limb bones (minimum diameter, minimum CSA, minimum circumference, wall thickness x diameter, etc.) and find out which one gives the best correlation with known masses of the animals they came from. Most likely we’d end up with some formula like mass =~ 4.5 x CSA ^ 0.94 + 3.1 x thickness ^ 0.561. It should be possible to find the best-fitting constants using simulated annealing, and the result would be a genuinely useful formula for estimating the masses of animals known only from limb bones. So (A) does anyone know if such a study has already been done, and (B) will anyone undertake to do it? (This was only on my Things To Do, Urgent! list, but has been buried under a stack of sauropods needing description.)

    Fifth, and most relevant: I noted earlier that “nearly all long bones are able to have cavities”. The reason for that “nearly” is of course that most sauropods have solid long bones. Why can that be? If it’s just to resist bending, then it would make more sense to distribute the same bone mass in hollow bones of greater diameter. Instead, the bones are solid … could it possibly be (and here I am speculating wildly) that sauropods got so big that their locomotion was so careful that, uniquely among animals, stresses were dominated by longitudinal crushing rather than bending? It would be great if someone were to look into this.

  17. Nathan Myers Says:

    Mike: Thank you for your detailed reply.

    The square-cube law isn’t as ferocious as the Central Limit Theorem, but for a critter substantially bigger than an elephant we should expect it to rule over everything else. (This raises the question, again, of what size benefit could have driven sauropods so far from the mainstream of practical body designs.) Solid lower limb bones must mean something, most likely the obvious thing.

    I can only add that any serious work on this subject must involve an engineer for the results to have any meaning.

    Oh, for the richness of too many sauropods needing description. If only that were true of early hominids.

  18. Randy Says:

    Oh, I didn’t mean to imply that the journal article should have cited it – obviously it was in press prior to my paper coming out. I just meant you should have cited it in the blog :)

    No excuses regarding not knowing about the article though, I assume you do subscribe to JVP. Plus, shouldn’t everyone be intimately familiar with my body of work ;)

    -R

  19. Matt Wedel Says:

    I’m coming to this late, but Re: the limb regression or volumetric mass estimate thread, the only study that I know of that compares the accuracy of the various methods is Hurlburt (1999), which used a bunch of lizards and alligators and included total length, snout-vent length, various limb-bone measurements, graphic double integration (GDI), and I think possibly also another volumetric method. The verdict: limb bone regressions suck, and they can be off by 100% or more. That’s not surprising; as Greg Paul pointed out, the Carnegie Diplodocus and Apatosaurus are roughly the same size, but limb bone regressions predict a 6-fold difference in mass. Volumetric methods predict at most a 1.5-fold difference. Of the methods Hurlburt examined, GDI is best, and even that can be off by as much as 20%.

    GDI also additional benefits, which are that it is fast, easy, and cheap. You can find a small pile of GDI refs (including Hurlburt) and a couple of examples (sans graphics, sadly) in the appendix to my latest paper.

  20. asier Says:

    Thanks Mike,

    Very interesting…

    I calculate the Xenoposeidon weight, with my personal technique jejejeje. About 15 tons…

    I have gotten this mass basing in the picture scale.

    For my calculation, I transformate Xauroposeidon Body, in a cylinder.

    First of all I take the Body + the legs(until knees, from the hips).

    The body is about 2.2 meters high, 1.8 meters wide and more than 3.5 meters long.

    We sum the height and wide 1.8 + 2.2 = 4, and then we divide by 2, = 2. So we have a cylinder of 2 meter of diameter and 3.5 meters high.

    If we fill with water this cylinder, it would weight–>

    (Pi x (2×2))x 3.5 = 44

    44/4 = 11 tons.

    The density of the dinosaur would be a bit less of water.
    So… 11 x 0.9 = 9.9 tons.

    Then we Sum the rest (the neck,tail and the rest of the four legs..) about 2 or 3 tons…

    We get a 12-13 tons Xenoposeidon.

    PD: answering the other question matt(brachiosaurus weight…).
    I don´t think that brachiosaurus has only 18 feet to the shoulders, because like I said, Mammuthus sungari has nearly 17 feet shoulder height.

    I refuse to think that a big mammoth is nearly as big as brachiosaurus.

  21. Matt Wedel Says:

    I don´t think that brachiosaurus has only 18 feet to the shoulders,

    You could be onto something here. Janensch’s skeletal reconstruction shows the shoulder at a bit over 6 meters, just a few inches over 20 feet. On the other hand, I have a hard time believing that our “stack of Mike” method, crude as it is, could be off by 2 whole feet. To further complicate matters, the photogrammetric measurement of the mounted Berlin skeleton by Gunga et al. (1995) shows the shoulder at about 5.8 meters, or 19.3 feet. So Janensch’s drawing, Gunga’s photos, and our (admittedly wacky) measurement of the Chicago mount all give different answers. And not trivially different, either–20 is a tenth greater than 18, which translates to a 33% greater mass. Mike, Darren, you guys want to weigh in (ha ha!) here?

    because like I said, Mammuthus sungari has nearly 17 feet shoulder height.

    Do you have a reference for this? I thought mammoths topped out at 14 or 15 feet in shoulder height. My information could be out of date. I’d be grateful for an update.

    I refuse to think that a big mammoth is nearly as big as brachiosaurus.

    I confess that I don’t follow your logic here. Even if Brachiosaurus was 20 feet at the shoulder, a 17-foot-tall mammoth would be nearly as big anyway. Refusal to believe doesn’t come into it. Hence my question about how secure the 17-foot height measurement for M. sungari is.

    Thanks for the interesting discussion.

  22. Mike Taylor Says:

    On the different shoulder-height measurements of Brachiosaurus

    First, what exactly do we mean by “shoulder height” here? And are we measuring the same thing in each case?

    Second, the Chicago mount is made up of an interesting combination of B. altithorax element casts, B. brancai casts for some of the missing elements, and out-of-thin-air sculpture for others, as discussed at http://scienceblogs.com/tetrapodzoology/2007/06/tet_zoo_picture_of_the_day_12.php

    So the humerus used in the Chicago mount is the 203 cm unreconstructed eroded humerus from the type material, which is 12 cm shorter than that of the Berlin specimen. If they reconstructed the other forelimb elements similarly shorter, that might go some way to explaining the mere 18-foot shoulder height.

    (Actually I quite like that idea, since it would also go some way to explain why the Chicago mount has a nearly horizontal mount whereas that of the Berlin mount slopes steeply upwards from the hip. Or at least, it did before Kristian Remes’s remount, I don’t know if it still does.)

  23. asier Says:

    Hi Matt,

    Here… Mammuthus sungari photo:

    .

    You can show it, in Ibaraki Nature museum (Japan). It was discovered in 1980. I´m pretty sure that is the biggest mammoth ever found.

    The webpage tells that the mammoth mesured 5.3 meters high and 9 meters long.

    PD: the 5.3 meters high, I don´t know if they are to the top of the head, or to th shoulders… Anyway is very gigantinc mammoth.

  24. asier Says:

    Sorry,

    I´ve had problems withj the server and it´s posted my post 2 times, please delete one of them.

    Sorry matt, I use the “<img src …” to show the photo but…
    Here a link to the giant mammoth.

    http://www.pref.ibaraki.lg.jp/bukyoku/seikan/kokuko/en/introduction/1994_1.html

    Mike,

    “shoulder height”,

    for me, is the distance from the floor to the top of the back before the neck..
    Not exctly to th shoulder…
    Is correct????

    Thanks.


  25. […] of the most complete 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 […]


  26. […] pick favourites. But from my own very biased perspective, I particularly enjoyed all eight days of the extended Xenoposeidon week, a rather exhausting series of posts that may make Xeno the most blogged […]


  27. […] including — finally — the publication of the table of brachiosaur mass-estimates that I alluded to back in Xenoposeidon week.  [Executive summary: published estimates for the single individual HMN SII have varied by a […]


  28. […] touched on this several times in various posts and comment threads, but it’s worth taking a moment to think in detail about the various […]


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: