How heavy was Giraffatitan brancai? I mean, really?

June 9, 2014

We’ve 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 published mass estimates for the single specimen MB.R.2181 (formerly known as HMN SII), the paralectotype of Giraffatitan brancai, which is the basis of the awesome mounted skeleton in Berlin.

Here is the table of published estimates from my 2010 sauropod-history paper, augmented with the two more recent estimates extrapolated from limb-bone measurements:

Author and date Method Volume (l) Density (kg/l) Mass (kg)
Janensch (1938) Not specified `40 t’
Colbert (1962) Displacement of sand 86,953 0.9 78,258
Russell et al. (1980) Limb-bone allometry 13,618
Anderson et al. (1985) Limb-bone allometry 29,000
Paul (1988) Displacement of water 36,585 0.861 31,500
Alexander (1989) Weighing in air and water 46,600 1.0 46,600
Gunga et al. (1995) Computer model 74,420 1.0 74,420
Christiansen (1997) Weighing in air and water 41,556 0.9 37,400
Henderson (2004) Computer model 32,398 0.796 25,789
Henderson (2006) Computer model 25,922
Gunga et al. (2008) Computer model 47,600 0.8 38,000
Taylor (2009) Graphic double integration 29,171 0.8 23,337
Campione and Evans (2012) Limb-bone allometry 35,780
Benson et al. (2014) Limb-bone allometry 34,000

(The estimate of Russell et al. (1980) is sometimes reported as 14900 kg. However, they report their estimate only as “14.9 t”; and since they also cite “the generally accepted figure of 85 tons”, which can only be a reference to Colbert (1962)”, we must assume that Russell et al. were using US tons throughout.)

The first thing to notice is that there is no very clear trend through time, either upwards or downwards. Here’s a plot of mass (y-axis) against year of estimate (x-axis):

I’ve not even tried to put a regression line through this: the outliers are so extreme they’d render it pretty much useless.

In fact, the lowest and highest estimates differ by a factor of 5.75, which is plainly absurd.

But we can go some way to fixing this by discarding the outliers. We can dump Colbert (1962) and Alexander (1989) as they used overweight toys as their references. We more or less have to dump Russell et al. (1980) simply because it’s impossible to take seriously. (Yes, this is the argument from personal incredulity, and I don’t feel good about it; but as Pual (1988) put it, “so little flesh simply cannot be stretched over the animal’s great frame”.) And we can ignore Gunga et al. (1995) because it used circular conic sections — a bug fixed by Gunga et al. (2008) by using elliptical sections.

With these four unpalatable outliers discarded, our highest and lowest estimates are those of Gunga et al. (2008) at 38,000 kg and Taylor (2009)at 23,337. The former should be taken seriously as it was done using photogrammetrical measurements of the actual skeletal mount. And so should the latter because Hurlburt (1999) showed that GDI is generally the least inaccurate of our mass-estimation techniques. That still gives us a factor of 1.63. That’s the difference between a lightweight 66 kg man and and overweight 108 kg.

Here’s another way of thinking about that 1.63 factor. Assuming two people are the same height, one of them weighing 1.62 times as much as the other means he has to be 1.28 times as wide and deep as the first (1.28^2 = 1.63). Here is a man next to his 1.28-times-as-wide equivalent:

I would call that a very noticeable difference. You wouldn’t expect someone estimating the mass of one of these men to come up with that of the other.

So what’s going on here? I truly don’t know. We are, let’s not forget, dealing with a complete skeletal mount here, one of the very best sauropod specimens in the world, which has been extensively studied for a century. Yet even within the last six years, we’re getting masses that vary by as much as the two dudes above.

19 Responses to “How heavy was Giraffatitan brancai? I mean, really?”

1. Michael Richmond Says:

Has anyone tried applying these same methods to estimate the mass of an extant animal? Say, for example, an elephant.

Would it be worth it for some members of this community to look out for a good opportunity. Perhaps some zoo has an elderly elephant and the facilities to weigh it. One could ask the zoo to weigh the animal, and one could take some photographs of it while it’s alive. When it dies, one could ask the zoo to strip off the meat (maybe as part of a pubic dissection event), then take the bones, clean them, and make them available to teams of paleozoologists. The teams could compete in several categories: full skeleton estimates, 30% skeleton estimates, and the crowd-pleasing estimates based on a single femur.

Sure, it would take some thousands of dollars and several weeks of work, and one has to wait for an animal in the proper environment to die, but would it be worth it?

For a much easier, cheaper, and quicker contest — one that takes just a weekend and a few hundred bucks — one could do the same thing with a cow.

2. Mike Taylor Says:

That’s a great idea, Michael.

The only downside with the cow version is that strict rules govern the disposal of livestock carcasses — in general, dead cows in the UK are supposed to be incinerated within 24 hours of death unless a post-mortem is to take place. I don’t know whether there would be a way to get those rules waived in the name of science.

3. Thomas Holtz Says:

Another issue to consider: how much does the body mass of an wild individual vary over the course of a year? Particularly with regards to issues of marked seasonality?

I wouldn’t be surprised if we find the same skeletal frame of a crocodile or elephant or rhino supporting quite variable amounts of flesh between the lean season and the fat.

(Larger hibernators, obviously, go through extremes. But I don’t suggest that sauropods were hibernators.)

4. Ian Corfe Says:

Bryan and Tom noted the weight varying over the year in the comments on the last post, and to me the 1.63x seems fairly reasonable for this, though I’ve been looking more at small hibernators recently for which 2x plus is normal… One thought is whether proximal limb circumferences are related to the maximum mass of an individual, not necessarily it’s ‘normal’, ‘fighting’ or ‘lean season’ weight? Would the regressions on these become even tighter if we were able to measure masses of the extant taxa at their heaviest? I recall some of the Anderson et al 1985 taxa were weighed in the dry/lean season though they allowed for this somehow.

5. Sean Says:

Off Topic (But still about sauropods!): Mike (And Matt as well.), what is your opinion on the new Cretaceous Diplodocid (From South America no less.)? You would think something like this would be well covered across blogs, but nobody seems to have noticed…

6. Mike Taylor Says:

Ian — really? A seasonal mass fluctuation factor of 1.63? I weigh near enough 100 kg as makes little difference for these mass discussions. I think my wife would be unimpressed if I seasonally put on another 63 kg.

7. LeeB Says:

Yes but how much would you weigh if you nearly starved for a month?
And then how much would you weigh if you then ate steadily to prepare for a lean season the following year?

Your weight might vary from around 70 to 130kg rather than increasing to 163kg.

LeeB.

8. Sean Says:

Wait, isn’t this based off the same specimen? If so seasonal variation can’t matter anyway. If not, age and health would obviously create such variation. Or am I just stupid?

9. While sauropods aren’t whales, it’s worth pointing out that Lockyer (1981) found that the average lean and fat ratios of blue whales can vary up to 49% between the lean condition in winter (March – Sept.) and the fat condition during feeding season in the summer (Oct. – Feb.); meaning a 70 tonne animal in lean condition could be more than 100 tonnes during the peak of the feeding season.

On a personal note, I am only about 1.5% taller than my dad, yet he weighs 40% more than I do. I’m guessing that if you had only our skeletons to go from, one would estimate a mass that would be a tie statistically-speaking (I’m sure a forensic anthropologist could probably determine which of us carried more weight around; although I’m not sure if one could still do that after being buried for 65.5+ million years).

I also might point out that when I did a GDI of Paul’s 1988 skeletal of Giraffatitan a few years ago, I got an estimated mass of about 30 tonnes, which is about 25% heavier than your published estimate. The problem is no one has actually published their GDI estimates in a rigorous fashion so it can be replicated or falsified. This is also true of volumetric model-based estimates like Greg Paul’s — we have to assume that his clay models reasonably conformed to his skeletals, which is a debatable assumption, and certainly not a very scientific one, in my opinion.

Ref–

Lockyer, C. (1981) Growth and energy budgets of large baleen whales from the Southern Hemisphere. FAO Fish. Ser. (5) [Mammals in the Seas] 3:379-487.

10. Mark Robinson Says:

Mike, humans are weird. I don’t think that it’s reasonable to assume that your apparent lack of seasonal variability is roughly equivalent with that of animals that weren’t able to drive to the supermarket and stock up come rain, hail, or shine. Note that I’m not saying that a factor of 1.63 × seasonal low to high is likely or even real. In this case it simply represents different assumptions regarding how much flesh overlay the skeleton. (Can’t even put it down to differences in assumed pneumaticity since you and Gunga et al. (2008) both use a density of 0.8).

Anyway, it’s not a factor of 1.63 – it obviously should be ~1.618, the golden ratio ;-)

11. MBR Says:

@Ian Corfe
Looking at modern hunter gatherers might give an idea of normal “natural” variation in humans, do they go from thin to morbidly obese depending on the season?

Another example might be artic foxes, Prestrud & Nilssen (1992) observed that their body fat percentage ranged from 6% in the summer to up to 20% in November.

Elephants are certainly better analogues but I’m not aware of any equivalent study, the closest is Klerk (2009) which used visual body condition estimations rather than measurements, mean body condition observed in non energy stressed individuals in Addo varied from good to very good depending on the season and not a ridiculous range of very thin to obese as is seen in bears or whales.

12. John Scanlon, FCD Says:

I was just thinking it would be really cool if the dots on that graph formed a rough outline of a brachiosaur…
But getting real, surely the value of these mass estimation techniques is to apply them to as many skeletons as possible and then interpolate across populations and taxa. Not to decry the awesomeness of the Berlin Giraffatitan mount (or the importance of seasonal/individual variation in soft-tissue mass), but there ought to be lots of inferences possible about palaeoecology based even on single-bone estimates.

13. Mike Taylor Says:

Of course applying techniques to many different individuals of many different species is of interest. The value of all these estimates of a single individual of Giraffatitan is that it shows very graphically how huge our error bars are.

14. Mark Says:

It’s probably just different fatness of the reconstructions. We really don’t know how much excess flesh was draped on the skeleton.

15. Mike Taylor Says:

That is probably a part of it. I don’t think it’s the whole story, though. Matt has long had a plan to present a multi-view restoration of an animal, together with a scalebar, and invite SV-POW! readers to run their own GDI on it. It would be interesting to see how much various people’s results differed.

16. […] für Naturkunde Berlin. Peer-reviewed published estimates of the mass of that one individual have varied between 13,618 and 78,258 kg — a factor of 5.75. Even if you discard these obvious outlier estimates, recent and credible estimates vary from […]

17. […] Giraffatitan) has been subject to at least 14 estimates in the published scientific literature, as summarised here. They vary from 13,618 kg to 78,258 kg — a factor of 5.75 for the same individual. […]

18. David Marjanović Says:

BM.R.2181

MB, not BM!

19. Mike Taylor Says:

Thanks, good spot! Now fixed.

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