Sauropod neural canals are weird, part 1: when the neural arch, um, isn’t one

May 31, 2017

Here’s a dorsal vertebra of Camarasaurus in anterior view (from Ostrom & McIntosh 1966, modified by Wilson & Sereno 1998). It is one of the most disturbing things I have ever seen in a sauropod. It makes my skin crawl.

Here’s why: the centrum and the thing we habitually call the ‘neural arch’ aren’t fully fused, and as this modified version makes clear, the ‘neural arch’ is neither neural nor an arch. Instead of being bounded ventrally by the centrum and dorsally and laterally by the neural arch, the neural canal lies entirely below the synchondrosis between the not-really-an-arch and the centrum.

Why?! WHY WOULD YOU DO THAT, CAMARASAURUS? This is not ‘Nam. This is basic vertebral architecture. There are rules.

Look at c6 of Apatosaurus CM 555 here, behaving as all good vertebrae ought to. Neural arch be archin’, as the kids say.

And if you are seeking solace in the thought that maybe the artist just drew that Cam dorsal incorrectly, forget it. I’ve been to Yale and examined the original specimen. I’ve seen things, man!

Camarasaurus isn’t the only pervert around here. Check this out:

Unfused neural arch of a caudal vertebra of a juvenile Alamosaurus from Big Bend. And I mean, this is a neural arch. This may be the most neural of all neural arches, in that it contains the entire neural canal. It’s more of a neural…ring, I guess. That’s right, this Alamosaurus caudal is batting for the opposite team from the Cam dorsal above. And it’s a team that neither you nor I play on, because we have well-behaved normal-ass vertebrae with neural arches that actually arch, and then stop, like God and Richard Owen intended.

Scientifically, my question about these vertebrae is: well, that is, I mean to say, what!? I think they have damaged me in some fundamental way.

If you have anything more intelligent to add (or even less intelligent – consider the gauntlet thrown down!), the comment thread is open.

References

  • Ostrom, John H., and John S. McIntosh. 1966. Marsh’s Dinosaurs. Yale University Press, New Haven and London. 388 pages including 65 absurdly beautiful plates.
  • Wilson, J. A. and Paul C. Sereno. 1998. Early evolution and higher-level phylogeny of sauropod dinosaurs. Society of Vertebrate Paleontology, Memoir 5: 1-68.
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15 Responses to “Sauropod neural canals are weird, part 1: when the neural arch, um, isn’t one”

  1. David Hone Says:

    Pterosaurs got you covered dude. Some have a neural canal *inside* the centrum:

    https://www.researchgate.net/publication/301770893_The_tuba_vertebralis_in_dsungaripterid_pterosaurs

  2. Matt Wedel Says:

    Thanks for this. But is the neural canal really within the centrum, or is the neural arch just really low and difficult to distinguish from the centrum? Unless there are juvenile verts that show the neural canal fully within the centrum prior to fusion of the neural arch, I don’t see how this is necessarily different from just having a long-ass, fully pneumatized camellate vertebra, such as you get in some birds and titanosaurs. Are there specimens that show where the neural canal was situated before neural arch fusion?

  3. David Hone Says:

    That might be harder to answer (i.e. I don’t know off the top of my head and I’d have to dig through quite a few papers and photos which may not provide a convincing answer). I’d potentially agree that this is something that was part of the neural arch kinda smushed into the centrum rather than developing as part of it, but even if that is the case, surely it’s a pretty extreme condition even compared to the ones above?

  4. Héctor Gómez de Silva Says:

    The neural canals of different vertebrates are clearly homologous to each other, centra are clearly homologous among themselves, and the “neural arches” are clearly homologous among themselves. That the neural canal does not always have the same relationship to the other two just means that “ontogeny finds a way” and the rules you believed existed are not that fixed.

    We tend to want things to be simple and linear, but Nature is full of complexities and surprises.

    I write this in the “if you have anything less intelligent to add” camp.

  5. Matt Wedel Says:

    surely it’s a pretty extreme condition even compared to the ones above?

    Not necessarily. In adult ratites and saltasaurids you get the same thing, with the neural canal suspended in a foam of pneumatic camellae, and all traces of the neurocentral synchondrosis remodeled and pneumatized away. Making such a vertebra flatter and longer, as in some pterosaurs, only changes the proportions, not the developmental relationships of the structures. When I get time I’ll knock up a sketch to illustrate the distinction and add it to the post.

  6. Matt Wedel Says:

    That the neural canal does not always have the same relationship to the other two just means that “ontogeny finds a way”…

    Beautifully put, Héctor.

    …and the rules you believed existed are not that fixed.

    Clearly not. But my antennae always twitch when I see one or a few groups of organisms breaking rules that seem to apply for all of the others. Why were sauropods able to get away with this, when (almost) everyone else seems constrained to build their vertebrae in the same way? Does it have something to do with the large size and fast growth of sauropods? Is it merely slop in the developmental program or is there some adaptive function?

    Hmm. I would have put those questions into the post, had they occurred to me in time. I’m planning on updating it anyway, so I will probably do so.

  7. Nima Says:

    That is literally the stupidest-looking vertebra I’ve seen. Cam has some mad virus going on there.

    No telling how many other sauropods had this craziness going on, that we don’t know about because no juvenile sutured specimens have turned up…

  8. Mark Konings Says:

    Perhaps it is a combination of large absolute size and the neural arch forming an enormous hypertrophied superstructure supporting very long processes which could act like levers wrenching the arch from the centrum. To prevent cracks from reaching the vital canal itself, with potentially fatal results, it would be beneficial to deflect them by removing the suture from the canal. This could be done by bringing the canal fully into the centrum, or fully into the arch.

  9. Matt Wedel Says:

    Combine Nima’s and Mark’s observations and I think we’re probably getting close to the truth. Getting the neurocentral joint away from the tiny, absurdly delicate spinal cord was probably smart, and loads of sauropods might have done this, but without unfused juvenile verts it’s nearly impossible to tell.

    Also probably relevant:

    Fronimos, J. A., & Wilson, J. A. (2017). Neurocentral Suture Complexity and Stress Distribution in the Vertebral Column of a Sauropod Dinosaur. Ameghiniana, 54(1), 36-49.

    They found that the neurocentral joints in sauropods are apomorphically complex, probably to distribute the stresses that sauropod vertebrae were under without ripping apart. Thanks to that work, we already know that sauropod neurocentral joints were probably under selection for resisting damage. Getting the joint away from the spinal cord would be the next step.

  10. Matt Wedel Says:

    Also:

    That is literally the stupidest-looking vertebra I’ve seen.

    You mean because of the weird neurocentral joint, right, and not just because it’s Camarasaurus?

    Sorry, had to be said!

  11. David Marjanović Says:

    I’ve seen some disturbing things. Postorbitals excluded from the orbit, intertemporals included in the orbit, pleurocentra ossified in four parts instead of two… But this here is unsettling.

    like God and Richard Owen intended.

    So full of win!

  12. Mike Taylor Says:

    David Marjanović channelling Roy Batty, there.

  13. John Scanlon Says:

    I’m with Héctor on this. Not all that different from grooves for cranial nerves or blood vessels that deepen and fuse into tunnels, or shallowen and disappear; or any topological character ever. Cool though.

  14. David Marjanović Says:

    Heh, “any topological character ever”… true, though.

    I’ve never heard or read of Roy Batty…

  15. David Marjanović Says:

    (Also, I’ve seen jugals excluded from the orbit by a lacrimal-postorbital contact.)


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