What a 23% longer torso looks like
September 20, 2009
Just checking: no-one’s bored of brachiosaurs yet, are they?
Thought not. Right, then, here we go!
Greg Paul’s (1988) study of the two “Brachiosaurus” species — the paper that proposed the subgenus Giraffatitan for the African species — noted that the trunk is proportionally longer in Brachiosaurus than in Giraffatitan due to the greater length of its dorsal centra. Paul (p. 7) stated that the difference is “25%-30%” on the basis of his figure 2.
Having seen the dorsal vertebrae of the type specimens of both species, my gut reaction was that the difference was nowhere near this great, so I recalculated it for myself (Taylor 2009:table 3). Dorsal column length is the sum of the “functional length” of the centra of the dorsal vertebrae, where functional length is the length of the centrum not counting the condyle (which of course is nestled in the preceding vertebra’s cotyle when the column is articulated). For Brachiosaurus, Riggs (1904) did not give this measurement, but did give total heights, and using these for scale I was able to measure the functional lengths from his plate LXXII. For Giraffatitan, Janensch’s (1950:44) superbly comprehensive table supplied measurements for D4 and D8; for D11 and D12 I was able to determine the length by measuring from Janensch’s (1950:fig. 62) figure, knowing the height from his table; and for D5-D7, D9 and D10, I interpolated linearly between the measurements that I had. Summing the functional lengths of D6-D12, I got 226 cm for Brachiosaurus and 183 cm for Giraffatitan. So Brachiosaurus is 226/183 = 1.23 times as long as Giraffatitan — in other words, 23% longer, which is pretty much what Greg Paul said. So I learned something there.
So: is a 23% longer torso a big deal? Back when I was trying to answer that question for myself, I figured it would help to take an image of a familiar animal and stretch it — so here is a horse, stolen from here and stretched:
To me, that second picture is wrong enough to hurt my eyes a little; your mileage may vary, but I suspect those among you who love horses will feel ill when you look at it. This image was one of the reasons — one of many — that I concluded that generic separation was unavoidable.
But here’s an odd thing: tonight, for this blog post, I did the same thing to a human body, expecting it to seem even more horrible in light of how familiar we are with our own bodies. Here it is:
To my surprise, the elongated human doesn’t look appallingly wrong to me. It doesn’t look right, of course, but it seems within the realms of, for example, what might appear as a representation of a human body in the early issues of Fantastic Four. I am not sure what to make of that fact. I don’t believe I have a more finely tuned sense of horse anatomy than human anatomy: it might be that I am more used to badly drawn humans than badly drawn horses; or that there is more variation in human proportions than in horse proportions; or maybe weirdness just looks less weird when it’s upright than when it’s horizontal. I’ll be interested to hear in the comments whether the Long Horse or the Long Human looks most wrong to readers.
(By the way, I casually talk about the type specimens of both “Brachiosaurus” species: while the situation is simple in the case of Brachiosaurus altithorax, whose holotype is FMNH P25107, things are more complex in the case of Giraffatitan brancai. Janensch nominated “Skelett S” as the holotype of his new species “Brachiosaurus” brancai, but that turned out to be a chimera, composed of the two skeletons which he subsequently designated SI and SII — but Janensch never designated one of these as the type, and so far as I’ve been able to determine, neither has anyone else done so. SI is represented by cranial elements and the first seven cervicals, but that’s all; SII is a much larger animal and is represented by most of the skeleton, and has been informally treated as though it were the type specimen most of the while, so I formally proposed HMN SII as the lectotype of the species (Taylor 2009:788) — just a bit of housekeeping.)
Here’s our old friend, the 8th cervical vertebra of HMN II, in a rare posterodorsal aspect, showing just how thin and, well, lamina-like the spinopostzygapophyseal laminae are. All that space in between them? Filled with diverticula, mostly. Amazing.
Meanwhile some good news:
Remember the good news and bad news about the all-dinosaurs special volume of The Anatomical Record? Well, since we posted that, the entire issue has been made open access! Fantastic stuff there: details from D. Schachne of the Wiley-Blackwell Communications Team. It’s not clear why the articles were all paywalled when originally posted, but all’s well that ends well.
And finally …
There’s been a gratifying amount of discussion in the comments on recent articles. It can be hard to keep track of, but it helped a lot when I found an RSS feed for comments, which is what I now use. For anyone else who wants it, it’s at http://svpow.wordpress.com/comments/feed/
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.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.Vesalius, A. 1543. Andreae Vesalii Bruxellensis, Scholae medicorum Patauinae professoris, de Humani corporis fabrica Libri septem [facsimile]. Ex Officina Ioannis Oporini, Basel, 659 pp.Wilson, Jeffrey A. 2006. Anatomical nomenclature of fossil vertebrates: standardized terms or “lingua franca”? Journal of Vertebrate Paleontology 26(3): 511-518.
- 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.
- 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.
- Vesalius, A. 1543. Andreae Vesalii Bruxellensis, Scholae medicorum Patauinae professoris, de Humani corporis fabrica Libri septem [facsimile]. Ex Officina Ioannis Oporini, Basel, 659 pp.
- Wilson, Jeffrey A. 2006. Anatomical nomenclature of fossil vertebrates: standardized terms or “lingua franca”? Journal of Vertebrate Paleontology 26(3): 511-518.