Happy Valentine’s Day from Apatosaurinae

February 15, 2021

This is RAM 1619, a proximal caudal vertebra of an apatosaurine, in posterior view. It’s one of just a handful of sauropod specimens at the Raymond M. Alf Museum of Paleontology. It’s a donated specimen, which came with very little documentation. It was originally catalogued only to a very gross taxonomic level, but I had a crack at it on a collections visit in 2018, when I took these photos. I told Andy Farke and the other Alf folks right away, I just never got around to blogging about it until now.

Why do I think it’s an apatosaurine? A few reasons: 

  • it’s slightly procoelous, which is pretty common for diplodocids, whereas caudals of Haplocanthosaurus, Camarasaurus, and Brachiosaurus are all either amphicoelous or amphiplatyan;
  • it has big pneumatic fossae above the transverse processes, unlike Haplo, Cam, and Brachio, but it lacks big pneumatic fossae below the transverse processes, unlike Diplodocus and Barosaurus
  • and finally the clincher: the centrum is taller than wide, and broader dorsally than ventrally.

In the literature this centrum shape is described as ‘heart-shaped’ (e.g., Tschopp et al. 2015), and sometimes there is midline dorsal depression that really sells it. That feature isn’t present in this vert, but overall it’s still much closer to a heart-shape than the caudals of any non-apatosaurine in the Morrison. Hence the literal 11th-hour Valentine’s Day post (and yes, this will go up with a Feb. 15 date because SV-POW! runs on England time, but it’s still the 14th here in SoCal, at least for another minute or two).

RAM 1619 in postero-dorsal view.

Back to the pneumaticity. Occasionally an apatosaurine shows up with big lateral fossae ventral to the transverse processes–the mounted one at the Field Museum is a good example (see this post). And the big Oklahoma apatosaurine breaks the rules by having very pneumatic caudals–more on that in the future. But at least in the very proximal caudals of non-gigantic apatosaurines, it’s more common for there to be pneumatic fossae above the transverse processes, near the base of the neural arch. You can see that in caudal 3 of UWGM 15556/CM 563, a specimen of Brontosaurus parvus:

I don’t think I’d figured out this difference between above-the-transverse-process (supracostal, perhaps) and below-the-transverse-process (infracostal, let’s say) pneumatic fossae when Mike and I published our caudal pneumaticity paper back in 2013. I didn’t start thinking seriously about the dorsal vs ventral distribution of pneumatic features until sometime later (see this post). And I need to go check my notes and photos before I’ll feel comfortable calling supracostal fossae the apatosaurine norm. But I am certain that Diplodocus and Barosaurus have big pneumatic foramina on the lateral faces of their proximal caudals (see this post, for example), Haplocanthosaurus and brachiosaurids have infracostal fossae when they have any fossae at all in proximal caudals (distally the fossae edge up to the base of the neural arch in Giraffatitan), and to date there are no well-documented cases of caudal pneumaticity in Camarasaurus (if that seems like a hedge, sit tight and W4TP). 

RAM 1619 has asymmetric pneumatic fossae, which is pretty cool, and also pretty common, and we think we have a hypothesis to explain that now–see Mike’s and my new paper in Qeios.

And if I’m going to make my midnight deadline, even on Pacific Time, I’d best sign off. More cool stuff inbound real soon.

References

12 Responses to “Happy Valentine’s Day from Apatosaurinae”

  1. Emanuel T Says:

    Hey there, do you have any location info associated with this vert? I assume it’s Morrison, but can we be sure?
    Cheers,
    Emanuel

  2. Mike Taylor Says:

    I’m gonna jump in here, because Matt told me the answer last night off-list:

    It was a donated specimen, with zero locality info. Literally on the specimen card the locality is, “matrix looks like the Morrison Formation”.

    :-)

  3. Andrea Cau Says:

    In Tataouinea, asymmetrical pneumatization affects the pelvis too: the left ilium, left ischium and left size of the caudal vertebrae are more pneumatic than their right equivalent.

  4. Matt Wedel Says:

    Andrea, that is very cool. I didn’t know that, but it’s believable. I’ve been quietly piling up examples of asymmetric pneumatization since the late 90s, should probably write a paper about it one of these days. Or at least a series of blog posts that I could turn into a paper later.

  5. Mike Taylor Says:

    I should probably write a paper about [asymmetic pneumatization] one of these days.

    Uh, dude? https://www.qeios.com/read/1G6J3Q

    I mean, OK, that was almost a month ago, fair enough. But still.

  6. Matt Wedel Says:

    That paper was about why pneumatization is asymmetric, but I could have made 10 more figures of examples. Just documenting the kinds of asymmetry — external features vs internal structure, or left/right fossae that are the same size and position but divided completely differently — is also valuable, I think.

  7. Emanuel T Says:

    got it, thank you! I suspected that would be the case. Too bad, but still a nice teaching and outreach specimen.

  8. Clarence Says:

    @ Mike Taylor, Matt Wedel.

    Good Day/Evening. Do you have any idea about the differences between the skulls of Brontosaurus and Apatosaurus which Drs. Mossbrucker and Bakker have revealed in a 2016 GSA abstract? Based on the limited information written in the 2016 abstract and a 23-minute youtube video posted February last year, they seem to imply that Brontosaurus have significantly more robust skull relative to Apatosaurus?

  9. Matt Wedel Says:

    Clarence, I haven’t followed that news. I think in this case I will wait for the paper — I want to see some solid evidence.

  10. Mike Taylor Says:

    Not that it would be a surprising finding, since apatosaurs have a more robust everything than diplodocines.

  11. Matt Wedel Says:

    Yeah, but I think he’s talking about an intra-Apatosaurinae difference between Brontosaurus and Apatosaurus. And I’m conflicted because I’m not sure which one is supposed to be the ‘skinny’ one.

  12. Clarence Says:

    @ Mike & Matt.

    What Matt said was exactly what I meant: intra-subfamily differences between the skulls of Brontosaurus and Apatosaurus (e.g. differences in dentition counts, braincase morphology, maxilla, etc.). The 2016 GSA abstract also seem to imply that Apatosaurus cervical vertebrae are more suited for horizontal brontosmash while the cervicals of Brontosaurus were constructed for brontosmash styles that mainly use vertical neck movements. This is the link on the youtube video:

    (https://www.youtube.com/watch?v=EbizH93i_Wk)


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