How much is our intuition about sauropod mass worth?
June 5, 2014
As promised, some thoughts on the various new brachiosaur mass estimates in recent papers and blog-posts.
Back in 2008, when I did the GDI of Giraffatitan and Brachiosaurus for my 2009 paper on those genera, I came out with estimates of 28688 and 23337 kg respectively. At the time I said to Matt that I was suspicious of those numbers because they seemed too low. He rightly told me to shut up and put my actual results in the paper.
More recently, Benson et al. (2014) used limb-bone measurements to estimate the masses of the same individuals as 56000 and 34000 kg. When Ian Corfe mentioned this in a comment, my immediate reaction was to be sceptical: “I’m amazed that the two more recent papers have got such high estimates for brachiosaurs, which have the most gracile humeri of all sauropods“.
So evidently I have a pretty strong intuition that Brachiosaurus massed somewhere in the region of 35000 kg and Giraffatitan around 30000 kg. But why? Where does that intuition come from?
I can only assume that my strongly held ideas are based only on what I’d heard before. Back when I did my 2008 estimate, I probably had in mind things like Paul’s (1998) estimate of 35000 kg for Brachiosaurus, and Christiansen’s (1997:67) estimate of 37400 for Giraffatitan. Whereas by the time the Benson et al. paper came out I’d managed to persuade myself that my own much lower estimates were right. In other words, I think my sauropod-mass intuition is based mostly on sheer mental inertia, and so should be ignored.
I’m guessing I should ignore your intuitions about sauropod masses, too.
References
- Benson Roger B. J., Nicolás E. Campione, Matthew T. Carrano, Philip D. Mannion, Corwin Sullivan, Paul Upchurch, and David C. Evans. (2014) Rates of Dinosaur Body Mass Evolution Indicate 170 Million Years of Sustained Ecological Innovation on the Avian Stem Lineage. PLoS Biology 12(5):e1001853. doi:10.1371/journal.pbio.1001853
- Christiansen, Per. 1997. Locomotion in sauropod dinosaurs. Gaia 14:45-75.
- Paul, Gregory S. 1998. Terramegathermy and Cope’s Rule in the land of titans. Modern Geology 23:179-217.
- Taylor, Michael P. 2009. A re-evaluation of Brachiosaurus altithorax Riggs 1903 (Dinosauria, Sauropoda) and its generic separation from Giraffatitan brancai (Janensch 1914). Journal of Vertebrate Paleontology 29(3):787-806.
Sauropod Vertebra Picture of the Week 
June 5, 2014 at 9:12 am
[…] More to come on this mass estimate real soon! […]
June 5, 2014 at 10:03 am
My 3D CAD model of Giraffatitan came out at ~45 metric tons, IIRC. Tweaking it from a Paul source to a Hartmann source lower this a tad, but not much.
Much of the intuitions simply is in the soft tissues…..
June 5, 2014 at 10:09 am
45 tonnes, interesting!
The underlying problem here is that most of us have no useful intuition about what any animal weighs. Show me a hippo or even a cow and I’d be hard-pressed to tell you its mass within, say 20%, maybe more. So what chance do we have of applying that intuition to fossil animals?
June 5, 2014 at 10:55 am
I’m guessing that, since most any tetrapod can vary in weight by at least fifty percent, all your intuitions are both correct and incorrect. Animals, in the wild, can starve, be well fed, be dehydrated, be well hydrated and so on. So, weight estimates by bone diameters, by displacement figured by models, by estimating the mass of various parts…lungs lighter, bones heavier, etc., are likely all within the ballpark of actual creature masses.
June 5, 2014 at 11:00 am
I certainly agree with that as a principle, Bryan. But the degree of variation in mass estimates for the same individual is sometimes so extreme that there’s no question some of them have to be complete nonsense. For example, as I showed in my sauropod history paper, published estimates for the single Giraffatitan brancai individual MB.R.2181 (= HMN SII) have varied from 13618 kg to 78258 kg, stopping at all stations in between.
June 5, 2014 at 11:11 am
Very interesting. I wonder if there is a trend resulting from how we imagine and draw dinosaur. Indeed we have heavy weight Giraffatitan in the beginning of the 20th and in the ninety skin wrapped sauropod. Does the estimation of Giraffatitan follow a temporal trend with a decrease till recently?
June 5, 2014 at 1:15 pm
I think that volumetric approaches are needed first before we can develop single-bone techniques. But these volumetric approaches absolutely need to be ground truthed in a wide sample of “knowns” of diverse body form.
June 7, 2014 at 6:09 am
78258 kg (Colbert’s estimate?) doesn’t even make sense for HMN XV2, let alone the smaller SII. Volumetric models are more predictable than bone-circumference techniques, but not all models are good. I’ve seen both extremely anorexic and extremely obese reconstructions for several sauropods. You models are only as good as your artist and their scientific knowledge.
June 8, 2014 at 8:32 am
Sounds like it’s time to reinvoke Matt’s Law of Biological Scaling.
June 8, 2014 at 11:26 pm
Sounds like it’s time to get rid of the “one estimate fits all” lunacy. IF we took a human skeleton, let’s say, an adult male, five foot ten, mesomorphic build and tried to say the guy weighed one hundred seventy pounds, then we’d probably realize that we are ignoring the fact that weights in a single individual can vary all over the map. As Mike said, some of the estimates are ridiculous, but what I myself find way more ridiculous is trying to estimate an exact weight for a fossil beast when getting exact weights for a living, breathing being is a crap shoot. Take your own self, for example; weigh yourself in the morning, afternoon, and evening and see if there’s any variance. Go on short commons for two weeks and tell me there’s no difference. Pig out when food is available and tell me there’s no difference.