Pneumatization sites: how does air get into vertebrae?

December 8, 2021

Science doesn’t always get done in the right order.

In the course of the research for my paper with Mike this past spring, “Why is vertebral pneumaticity in sauropod dinosaur so variable?”, published in Qeios in January, I had a couple of epiphanies. The first was that I had collated enough information to map the sites at which arteries and veins enter and exit the vertebrae in most tetrapods. The second was that, having done that, I’d also made a map of (almost) all the places that diverticula enter the vertebrae to pneumatize them. This is obviously related to the thesis we laid out in that paper, that postcranial skeletal pneumaticity is so variable because pneumatic diverticula follow pre-existing blood vessels as they develop, and blood vessels themselves are notoriously variable. In fact, if you had to summarize that thesis in one diagram, it would probably look like the one above, which I drew by hand in my research notebook in early March.

Only that’s not quite correct. I didn’t have those epiphanies “in the course of the research”, I had them after the pneumatic variation paper was done and published. And at the time they felt less like epiphanies and more like a series of “Holy crap” realizations:

  1. Holy crap, that diagram would have been really helpful when we were writing the pneumatic variation paper, since it establishes, almost tautologically, that diverticula invade vertebrae where blood vessels already have. In a rational world, Mike and I would have done this project first, and the pneumatic variation paper would have stood on its shoulders.
  2. Holy crap, how have I been working on vertebral pneumaticity for more than two decades without ever creating a map of all the places a vertebra can be pneumatized, or even realizing that such a map would be useful?
  3. Holy crap, how have I been working on dinosaur bones — and specifically their associated soft tissues — for more than two decades without wondering exactly how the blood was getting into and out of each bone? 

Arguably, not only should Mike and I have done this project first, I should have taken a stab at it way back when I was working on my Master’s thesis. Better late than never, I guess.

I used a sauropod caudal as my vertebral archetype because it has all the bits a tetrapod vertebra can have, including the hemal arch or chevron. This was important, because Zurriaguz et al. (2017) demonstrated that the chevrons are pneumatic in some titanosaurs. 


For the actual presentation I redrew the vessels on top of a scan of a Camarasaurus caudal from Marsh, which Mike found and cleaned up (modified from Marsh 1896: plate 34, part 4, and plate 39, part 3c). 

We deliberately used an unfused caudal to emphasize that ‘ribs’ — technically, costal elements — are present, they just fuse to the neural arch and centrum rather than remaining separate, mobile elements like dorsal ribs.

Anyway, I’m yapping about this now because this project is rolling: Mike and I submitted an abstract on it for the 3rd Palaeontological Virtual Congress, and a short slideshow on the project is now up at the 3PVC site for attendees to look at and comment on. The congress started last Wednesday and runs through Dec. 15, after which I’m sure we’ll submit the abstract and slide deck somewhere as a preprint, and then turn it into a paper as quickly as possible.

I’ll probably have more to say on this in a day or so, but for now the comment field is open, and your thoughts are welcome.



5 Responses to “Pneumatization sites: how does air get into vertebrae?”

  1. Allen Hazen Says:

    So, since you didn’t post it ten years ago, what the rest of us can do is go back over your earlier posts with this in hand. I think it is REALLY helpful in understanding what’s going on! Helps in seeing the pattern to the perplexing plethora of particulars which you’ve presented of different degrees and areas of pneumatization.

  2. Allen Hazen Says:

    Ah. One minor mystery (mystery, maybe, only to me in my ignorance) solved. Those big fat vessels — caudal artery, caudal vein — in the lower arch. So THAT’S why chevrons are sometimes called HAEMAL arches!

  3. David Marjanović Says:


    Wait. There are unfused caudal ribs in Camarasaurus? I thought that never happened in, like, crown-group sauropsids or something.

  4. Matt Wedel Says:

    There are unfused caudal ribs in the proximal caudal vertebrae of subadults of all sauropods, as far as I know. Gallina and Otero (2009) concluded that unfused transverse processes of sauropod proximal caudals are ribs, and that’s consistent with how tetrapod vertebrae ossify in general. I have a tickle at the back of my brain that this has gotten some more discussion in the last decade or two, but at the moment I can neither remember the details nor find the relevant paper(s). Anyway, in all proximal caudals of subadult sauropods that I’ve seen, there’s either an incompletely-fused blob that looks like a wimpy sacral rib, or a joint for that element, and I have no idea what those might be other than costal elements. Alligator caudals look the same. If anyone has more details, or alternative hypotheses, I’d love to know more.

    Gallina, P.A. and Otero, A. 2009. Anterior caudal transverse processes in sauropod dinosaurs: morphological, phylogenetic and functional aspects. Ameghiniana 46(1):165-176.

  5. ReBecca Hunt-Foster Says:

    This would be a cool 3D model/cutaway that could be used in an exhibit where there are lots of sauropods. I know of such a place….

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