How big was Futalognkosaurus?
January 16, 2008
Futalognkosaurus dukei, just described last year, may be the most complete giant dinosaur ever discovered. Maybe. Depends on what you compare it to, and it also depends on how it’s measured. It’s hard to say right now because only one short paper on it has been published to date (Calvo et al. 2007), and it only includes one figure of the beast. Let’s take a look.
Figure 2 from Calvo et al. (2007)
Now, according to the skeletal reconstruction and the 2 meter scale bar, the total length of the cervical series is 10.6 meters, the dorsal column is 4.85 meters long, and the sacrum is 1.75 meters long. By way of comparison, the complete cervical series of the HM SII skeleton of Brachiosaurus brancai is 8.5 meters (or would be, with the two missing cervicals included), and the really complete, articulated neck of Mamenchisaurus hochuanensis is 9.5 meters. So Futalognkosaurus indeed looks like a whopper.
But hang on a second. The figure also includes scale photos of several of the elements. It’s a cinch to use those scale bars to figure the size of the photographed elements, and compare the measurements obtained that way to the size of the same elements in the skeletal reconstruction. I made all the measurements using the ruler tool in Photoshop, and here’s what I got (feel free to do your own and compare). In each line, the first number is the one I get from the scaled skeletal reconstruction, the second is the number I get from the scaled photograph, and in parentheses is the second as a percentage of the first.
- C2 is 18 cm … or 29 cm (161%)
- C6 is 79 cm … or 46 cm (58%)
- C10 is 94 cm … or 89 cm (95%)
- C14 is 94 cm … or 50 cm (53%)
- Caudal 1 is 92 cm tall … or 72 cm tall (78%)
- Pubis is 149 cm … or 141 cm (95%)
Now, it’s interesting that except for C2, which is small and hard to draw right (trust me), all of the measurements based on photos are smaller than the measurements based on the skeletal reconstruction.
The only measurement given in the paper–other the total length of the animal, estimated at 32-34 meters (105-111 feet)–is the length of the pubis, which is actually 137 cm, which is 97% of the size indicated by the scaled photo and 92% of the size indicated by the skeletal reconstruction.
The story gets more interesting. As you can see from the numbers I slapped on the illustration, the reconstruction includes 14 cervicals, 11 dorsals, 6 sacrals, and 1 caudal. But in the character matrix at the end of the paper, Futalognkosaurus is coded as having 14 cervicals, 10 dorsals, and 6 sacrals. So either the skeletal reconstruction has an extra vertebra, or the dorsal count is miscoded.
If the skeletal reconstruction is accurate (and everything else wrong), the total length of the neck, trunk, and sacrum is 17 meters, so a total length of 30+ meters is pretty reasonable. But if everything else is right, the skeletal reconstruction is too big, by anywhere from 5-47%. I don’t think it’s really half again too big, but I’ll bet that the real number is lurking in there somewhere, probably around 15%.
So what’s the point? Why did I write the post?
Well, I certainly didn’t do it to make Calvo et al. look careless or stupid. The fact is, it is really, really easy to get scale bars wrong, and really, really hard to get skeletal reconstructions right. I have screwed up both (see Wedel 2000 for evidence). Big things are hard to measure, and it is perilously easy to get the numbers wrong. In the original paper on Sauroposeidon I (my coauthors are blameless here) wrote that it had 12-meter neck, the longest of any known animal. Turns out neither of those things is true. The most liberal neck estimate for Sauroposeidon is 11.5 meters, and the most conservative is only 10.5 meters. And Supersaurus had a longer neck, at least 13 or 14 meters no matter how you get there (Wedel and Cifelli 2005).
Here’s another example. Crack open just about any dinosaur book and you’ll read that Mamenchisaurus had a neck 33 feet long. But it ain’t the case. Tote up the lengths of the individual vertebrae in Young and Zhao (1972) and you’ll get 31.5 feet (9.5 meters). Stretch a tape measure along the mounted skeleton and you’ll get the same result. So where did the number 33 come from? Beats me. But a lot of people have repeated it, when the real numbers are not hard to get (at least for the people doing the repeating).
Also, I can’t fault Calvo et al. for publishing a short description of Futalognkosaurus, as long as they follow up with something more substantial later. It’s pretty common in biology (not just paleo), and it’s exactly what Rich and Kent and I did with Sauroposeidon. Describing things is a time-consuming process–four measly vertebrae were enough to keep me busy for years–and there are lots of reasons why it may be good to get something out now and follow up with the monograph as time and circumstances allow (but do follow up).
I wrote the post for the same reason I do all this stuff–when it comes to sauropods and their vertebrae, my curiosity knows no bounds. As soon as I saw the Futalognkosaurus description I knew I’d eventually dig in and see how big the critter is supposed to be. And now I have an outlet for that kind of nerdosity, hence the post.
The moral of the post, if there is one, is that tables of measurements are usually harder to screw up than scaled figures (but by no means invulnerable to error). And that until a more complete description of Futalognkosaurus appears–hopefully with a table of measurements–it’s hard to say how big it was. Maybe it was bigger than Brachiosaurus. Maybe not.
- Calvo, J.O., Porfiri, J.D., Gonzalez-Riga, B.J., and Kellner, A.W.A. 2007. A new Cretaceous terrestrial ecosystem from Gondwana with the description of a new sauropod dinosaur. Anais da Academia Brasileira de Ciencias 79(3):529-541.
- Wedel, M.J. 2000. Reconstructing Brachiosaurus. Prehistoric Times 42:47.
- Wedel, M.J., and Cifelli, R.L. 2005. Sauroposeidon: Oklahoma’s native giant. Oklahoma Geology Notes 65(2):40-57.
- Young, C.C., and Zhao, X.-J. 1972. Mamenchisaurus hochuanensis sp. nov. Institute of Vertebrate Paleontology and Paleoanthropology Monographs, A, 8:1-30.