Your torso is also pretty lame
February 21, 2008
Following on from Your neck is pathetic, I offer you the fifth presacral vertebra of the Brachiosaurus altithorax holotype specimen FMNH P25105, in right lateral view, with a complete human dorsal column for scale.
Why is this vertebra designated “presacral 5″? Because the Brachiosaurus holotype specimen included an articulated set of the last seven dorsal vertabrae (and the sacrum, two caudals, a coracoid, humerus, ilium, femur and some ribs) but none of the more anterior dorsals. Rather than guess how many dorsals there were in life, so that he could assign serial positions to the seven that were preserved, Riggs (1903) very sensibly just counted forward from the sacrum.
So how many dorsals did Brachiosaurus have? We must have plenty of better specimens by now, right? Wrong: despite more than a century of fossil-hunting in North America, Riggs’s specimen, which he described in detail in 1904, remains by far the best and most complete that has been described in the published literature. All the other specimens that are of any scientific value consist of isolated or doubtfully associated elements, and in any case have not been described anywhere near as well as Riggs dealt with his material. There are apparently some much better specimens in private hands, but, well, they are effectively lost to science — at least until the owners die.
When Janensch (1914, 1950) described the African species Brachiosaurus brancai from Tendaguru in Tanzania, he reconstructed it with 11 dorsals, and that number has been pretty much accepted ever since. However, as pointed out by Paul (1988), Migeod’s (1931) description of a Tendaguru brachiosaurid that has been generally accepted as a specimen of B. brancai indicated that it had at least 12 dorsals. Although Migeod’s specimen is probably generically distinct from both B. altithorax and B. brancai (Taylor 2005), it still provides the best evidence we have of the vertebral formula in brachiosaurids. So, twelve it is, until better evidence turns up. Distressingly, none of the other brachiosaurids or putative brachiosaurids that we know about (Sonorasaurus, Cedarosaurus, Sauroposeidon, etc.) have specimens with complete dorsal columns.
Oh, and how many dorsals do humans have? Twelve thoracics and five lumbar vertebrae, for a grotesquely inflated total of 17. The distinction between thoracics (which bear ribs) and lumbar vertebrae (which do not) is standard for mammals, but does not apply for reptiles, in which all dorsals bear ribs. (At least, that’s true in sauropods, which is all that matters.)
- Janensch, Werner. 1914. Ubersicht uber der Wirbeltierfauna der Tendaguru-Schichten nebst einer kurzen Charakterisierung der neu aufgefuhrten Arten von Sauropoden. Archiv fur Biontologie, Berlin, III, 1(1):81-110.
- Janensch, Werner. 1950. Die Wirbelsaule von Brachiosaurus brancai. Palaeontographica (Suppl. 7) 3:27-93.
- Migeod, Frederick W. H. 1931. British Museum East Africa Expedition: Account of the work done in 1930. Natural History Magazine 3(19): 87-103.
- 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.
- Riggs, Elmer S. 1903. Brachiosaurus altithorax, the largest known dinosaur. American Journal of Science 15(4):299-306.
- Riggs, Elmer S. 1904. Structure and relationships of opisthocoelian dinosaurs: Part II, the Brachiosauridae. Field Columbian Museum, Geological Series 2, 6:229-247, plus plates LXXI-LXXV.
- Taylor, Michael P. 2005. Sweet seventy-five and never been kissed: the Natural History Museum’s Tendaguru brachiosaur; p. 25 in Paul. M. Barrett (ed.), Abstracts volume for 53rd Symposium of Vertebrae Palaeontology and Comparative Anatomy. The Natural History Museum, London. (Yes, it’s bad form for me to cite my own abstract. Sorry: the key point has yet to appear in “proper” published literature.)