Your cervical ribs are (probably) non-existent
December 2, 2009
It’s a strange thing, but no-one seems to bother properly figuring their sauropods’ cervical ribs — that is, the long, thin, posteriorly directed ribs of the neck vertebrae. I’ll be bucking that trend when the Archbishop paper comes out, but to get your mouth watering ahead of time, here is the head of the cervical rib that I have arbitrarily designated X1, the largest of those preserved in the Archbishop:
The top image shows the rib in anterior view, with dorsal pointing to the left; the middle row shows the rib with anterior pointing upwards, in (from left to right), lateral, dorsal, medial and ventral views; the bottom row shows posterior view, again with dorsal to the left. Click through the image to see the full glory of the high-resolution version. Remember folks: you only get this sort of high-resolution image published in PLoS journals!
As I mentioned, sauropod cervical ribs have been pretty comprehensively ignored in the literature. I can’t offhand think of a single paper about them (unless you count Martin et al.’s (1998) proposal that they functioned in ventral compression-bracing of sauropods’ necks, and let’s not even start on that), and I am really struggling to think of paper that figures them. Even the usually super-reliable Osborn and Mook (1921) dropped the ball here, with a single illustration (out of 127 figures) and single short paragraph of text (out of 141 pages). Here it is:
Janensch (1950) did discuss the cervical ribs of Giraffatitan in some detail, but his figures are not very informative. If anyone knows of better treatments of sauropod cervical ribs in the literature, then please mention it in the comments!
Because of this poor coverage in the published record, it’s hard for me to compare the Archbishop cervical ribs with those of other taxa. For example, the medial view of X1 (in the middle of the “cross” in the image above) shows that the internal face of the cervical rib loop, where the cervical rib reaches up to articulate with the diapophysis of its vertebra, has two parallel struts of bone extending vertically with a narrow groove between them. Is that unusual? I have no idea.
(I do have photos of some other Tendaguru cervical ribs, referred to Giraffatitan – although if I’m right that the Archbishop is not Giraffatitan, so that there are multiple brachiosaurs in the Tendaguru Formation, then who knows whether that referral is correct?)
Finally, we come to the matter of your cervical ribs. I would have liked to do this post as one in the Your Noun Is Adjective series, but the brutal truth is, you don’t even have any cervical ribs — unless you are one of the lucky 0.2% that, according to the Wikipedia article, have a supernumary rib which is frankly just an additional dorsal rib (uh, thoracic rib I guess) that’s growing out of your last cervical vertebra by mistake. (Wikipedia’s horrible humanist bias is apparent here, in that the article doesn’t even mention the fact that plenty of other animals have cervical ribs and love them.)
Anyway, here’s how human cervical ribs look, stolen from Do You Really Need Back Surgery? A Surgeon’s Guide to Neck and Back Pain and How to Choose Your Treatment:
- Janensch, Werner. 1950. Die Wirbelsaule von Brachiosaurus brancai. Palaeontographica (Suppl. 7) 3:27-93.
- Martin, John, Valérie Martin-Rolland, and Eberhard (Dino) Frey. 1998. Not cranes or masts, but beams: the biomechanics of sauropod necks. Oryctos 1:113-120.
- Osborn, Henry Fairfield, and Charles C. Mook. 1921. Camarasaurus, Amphicoelias and other sauropods of Cope. Memoirs of the American Museum of Natural History, n.s. 3:247-387, and plates LX-LXXXV.