Did apatosaurs have unusually large neural spines, too?

June 22, 2018

We all know that apatosaurines have big honkin’ cervical ribs (well, most of us know that). But did they also have unusually large neural spines?

The question occurred to me the other day when I was driving home from work. I was thinking about C10 of CM 3018, the holotype of Apatosaurus louisae, and I thought, “Man, that is a lot of neural spine right there.”

Why was I thinking about C10, particularly? I traced and also stacked Gilmore’s (1936) drawing for my 2002 paper with Kent Sanders, and recycled the trace for my 2007 prosauropod paper, and recycled the stack-o-C10s for my 2013 PeerJ paper with Mike. So for better or worse C10 is my mental shorthand for A. louisae, the same way that their respective C8s seem to capture the essence of Giraffatitan and Sauroposeidon.

I decided that the quick-and-dirty solution was to compare the vertebrae of A. louisae with those of Diplodocus carnegii, the default reference diplodocid, and see how they stacked up. With the cotyles scaled to the same vertical diameters, this is what we get for C9 and C10 of CM 3018 (lighter gray, background, traced from Gilmore 1936) vs CM 84/94 (darker gray, foreground, traced from Hatcher 1901):

The A. louisae verts are a hair taller, proportionally, than those of D. carnegii, but not by much. The difference is trivial compared to the differences in centrum length and cervical rib size.

So where did I get this apparently erroneous impression that Apatosaurus had giant neural spines? Maybe it’s not that the neural spines of apatosaurines in particular are so large, but rather than diplodocids of all types have large neural spines compared to non-diplodocids. Here are the same vertebrae compared for D. carnegii (dark gray, background) and Camarasaurus supremus (black, foreground, traced from Osborn and Mook 1921):

I deliberately picked the longest C9 in the AMNH collection, and the least-distorted C10. The first surprise for me was how well this C. supremus C9 hangs with D. carnegii in terms of proportions. That is one looooong Cam vert. In any other sauropod, it would probably be beautiful. But because it’s Camarasaurus it attained its length in the most lumpen possible way, with the diapophysis way up front, the neural spine apex way at the back, and in the middle just…more vertebra. Like a stretch limo made from a Ford Pinto, or Mike’s horrifying BOBA-horse.

Inevitable and entirely justified Cam-bashing aside, it’s striking how much smaller the whole neural arch-and-spine complex is in C. supremus than in D. carnegii. And remember that D. carnegii is itself a bit smaller than Apatosaurus, spine-wise. Is this maybe a diplodocoid-vs-macronarian thing, at least in the Morrison? Here’s the C10 stack with Brachiosaurus included, represented by BYU 12867 (which I think is probably a C10 based on both centrum proportions and neural spine shape – see Wedel et al. 2000b for details), and with labels added because it’s getting a little nuts:

I like this; it shows a lot. Here are some things to note:

  • The diplodocids don’t just have taller neural spines, their pre- and postzygapophyses are also higher than in the macronarians. That’s gotta mean something, right? All else being equal, putting the zygs farther from the intervertebral joints would reduce the flexibility of the neck. Maybe diplodocoids could get away with it because they had more cervicals, or maybe their necks were stiffened for some reason.
  • The zygs being set forward of their respective centrum ends in the macronarians really comes through here.
  • The Brachiosaurus vert isn’t that different from a stretched (and de-uglified) Cam vert, with a slightly higher neural spine to help support the longer neck. (Maybe this is why Cam inspires such visceral revulsion: it reads as a failed brachiosaur.)
  • This emphasizes the outlier status of Apatosaurus in the cervical rib department. It bears repeating: the cervical ribs of Camarasaurus are certainly wide, but they’re not nearly as massive or ventrally expanded as in apatosaurines.

So far, pretty interesting. I’d like to add Barosaurus and Haplocanthosaurus to round out the “big six” Morrison sauropods. I known Haplo has big, tall, almost apatosaurine neural spines (as shown above, with arrows highlighting the epipophyses), but for Baro I’d have to actually do the comparison to see where it falls out.

The idea of bringing in Barosaurus also forces the question, previously glossed over, of how legit it is to compare C10s of all these animals when their cervical counts differed. C. supremus is thought to have had 12 vertebrae in its neck, Brachiosaurus 13 (based on Giraffatitan), A. louisae and D. carnegii 15, and Barosaurus probably 16. It would be more informative to graph neural spine height divided by cotyle diameter along the column for all of these critters, plus Kaatedocus and Galeamopus. But that’s a lot of actual work, and as much fun as it sounds (really, I’d rather be doing that), I have summer teaching to prep for and field gear to wrangle. So I’ll have to revisit this stuff another time.

References

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10 Responses to “Did apatosaurs have unusually large neural spines, too?”

  1. Mike Taylor Says:

    “With the cotyles scaled to the same vertical diameters …”

    That seems like a strange scaling criterion, especially as we know all too well how easily cotyle rims deform, giving a false impression. Surely scaling to centrum length is less error-prone.

    (Also, while you’re re-doing the image, you might as well use different colours for the two vertebrae rather then two different greyscales.)

  2. Mike Says:

    Very interesting ! How about the actual shape of the neural spines ? Can the shape help aid in genus identification and/or cervical position, as not only height but shape appear to vary considerably when comparing your examples. Higher defined peak, more sloping, etc.

  3. Mike Taylor Says:

    Yes, absolutely! Apatosaurs have very distinctive neural spines that are one of the most recognisable features of their skeletons.

  4. Andrew Stuck Says:

    What does the enlarged neural spine mean mechanically speaking? Does this provide additional support for BRONTOSMASH at all, or not necessarily?

  5. Brad Lichtenstein Says:

    …and absolute size matters, I would think less than relative size: the deflection of a rigid span is generally proportional to the cube of its length, iirc. But if Cam generally had shorter necks, then they needed less force and thus fewer and shorter muscle attach points to hold themselves erect. Right?

  6. Matt Wedel Says:

    What does the enlarged neural spine mean mechanically speaking?

    Presumably more area for muscle attachment.

    Does this provide additional support for BRONTOSMASH at all, or not necessarily?

    It doesn’t hurt. It’s part of the whole package of apatosaurs having ridiculously overbuilt, heavy necks, which flies in the face of at that point about 80 million years of sustained evolution toward longer, lighter necks. They must have had some persuasive selection pressure for making their necks fatter and heavier, and often when we see bizarre structures, they’re for sexual display or combat.

    But if Cam generally had shorter necks, then they needed less force and thus fewer and shorter muscle attach points to hold themselves erect. Right?

    Presumably. Cam is pretty shockingly short-necked for a big sauropod. Even the humongous AMNH C. supremus only had a neck about 4m long. A diplodocid of the same body size would have a neck 7-9m long, a brachiosaur 8-10m long, and a mamenchisaur even longer.

  7. Matt Wedel Says:

    Belatedly getting back to this:

    “With the cotyles scaled to the same vertical diameters …”

    That seems like a strange scaling criterion, especially as we know all too well how easily cotyle rims deform, giving a false impression. Surely scaling to centrum length is less error-prone.

    If you were comparing a cow, an okapi, and a giraffe, would you scale the cervical centra by length or by diameter? I think all we would learn from scaling to the same length is that some sauropods had long cervicals and others had shorter ones.

    Tell you what – I will email you the GIMP file and you can play with it at your leisure.

  8. Mike Taylor Says:

    “you were comparing a cow, an okapi, and a giraffe, would you scale the cervical centra by length or by diameter?”

    Depends what I was trying to discover about the vert shape.

    “I will email you the GIMP file and you can play with it at your leisure.”

    … waiting …

  9. Matt Wedel Says:

    Fixed. Feel free to make your own and post ’em.


  10. […] course I started out by making fun of the most mockable sauropod. This one’s for you Cam-loving perverts out there. You know who you […]


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