The dark side of Sauroposeidon

February 4, 2013

Sauroposeidon OMNH 53062 C7-C8 left side

Sauroposeidon holotype OMNH 53062, posterior half of ?C7 and all of ?C8 in left lateral view. Scale bar is in inches.

There’s a lot more Sauroposeidon material these days than there used to be, thanks to the referral by D’Emic and Foreman (2012) of Paluxysaurus and Ostrom’s Cloverly material and the new Cloverly material to my favorite sauropod genus. I’ve seen almost all of this material firsthand, but obviously the specimen I’m most familiar with is the holotype, OMNH 53062. It was the primary thing occupying my mind from the summer of 1996 through the spring of 2000, and it has remained a frequent object of wonder ever since.

The specimen was found lying on its right side in the field, so that side is in better shape, by virtue of having been more deeply buried and thus protected from the ravages of freezing and thawing and other erosional processes. When the jackets were taken out of the ground and prepared, the not-so-well-preserved left sides were prepped first. Then permanent support jackets were made on the left sides, the vertebrae were flipped onto their left sides, the field jackets were removed from their right sides, and the vertebrae were prepped on the right. They’ve been lying in their support jackets, left side down and right side up, ever since. (For more on the taphonomy and recovery of the specimen, see this post and Wedel and Cifelli 2005 [free PDF linked below].)

Now, if I had known what I was doing, I would have photographed the crap out of the left sides before the verts were flipped. But it was my first project and I was learning on the job, and that didn’t occur to me until later.

It also didn’t occur to me that, once flipped, the left sides would be effectively out of reach forever. But the vertebrae are extremely fragile. The bigger verts have cracks running through them, and the jackets flexed noticeably when we took them for CT scanning. I am worried that if we tried to flip the bigger verts today, they might just crumble. Even the surface bone is fragile. I remember once trying to get some dust off one of the verts with a vacuum cleaner hose, and watching in horror as some of the millimeter-thin external bone just flaked off and flew away. That was in the late 1990s, when the verts were still stored in the dusty, drafty WWII-era buildings that had housed the museum collections for ages. Now they’re in what I still think of as the “new” building, which opened in 2000, in a really nice modern collection room with climate and dust control, and I’ve never seen them with any noticeable dust.

Anyway, the left sides are now obscured by their supporting jackets and will remain that way for the foreseeable future. And I don’t have a complete set of photos of the left sides of the verts. But I do have one, of the back half of ?C7 and all of ?C8, and a scan of it appears at the top of this post. It’s a scan of a physical photograph because it was taken in late 1996 or early 1997–no-one I knew had a digital camera, and if you wanted a digital version of a photograph, you shot it on a film camera, had a big print made, and scanned that on a flatbed scanner.

Here’s another version with the vertebrae outlined:

Sauroposeidon OMNH 53062 C7-C8 left side - outlined

When I and everyone else thought that Sauroposeidon was a brachiosaur, I was pretty sure that these were C7 and C8, out of a total of 13 cervicals, just like Giraffatitan. And it still might be so–a future analysis might find that the newly-expanded Sauroposeidon is a brachiosaurid after all, and even if not, Gomani (2005) posited a primitive cervical count of 13 for titanosaurs. If that’s true, then possibly 13 cervicals are primitive for all titanosauriforms, and the increases beyond that–to 17 in Euhelopus and 14-17 in more derived titanosaurs like Futalognkosaurus and Rapetosaurus–were deviations from that primitive pattern.

But.

If Sauroposeidon was a basal somphospondyl, as posited by D’Emic and Foreman (2012) and as found in the phylogenetic analysis of D’Emic (2012), then maybe it was more like Euhelopus than Giraffatitan, and maybe it had more than 13 cervicals. (Note that D’Emic [2012] found Sauroposeidon to be a basal somphospondyl but outside the Euhelopodidae, so even in his analysis, Euhelopus could have gotten its extra cervicals independently of Sauroposeidon.) That’s an interesting prospect, since the 11.5-meter neck estimate for Sauroposeidon I made back in 2000 was based on the conservative assumption of 13 cervicals. If Sauroposeidon had more cervicals, they were probably mid-cervicals (nobody adds more dinky C3s, or stubby cervico-dorsals*–that would be silly), and therefore between 1 and 1.25 meters long. So if the individual represented by OMNH 53062 had 15 cervicals, as Mike hypothetically illustrated in this post, its neck might was probably more like 14 meters long, and if it had 17 cervicals, like Euhelopus and Rapetosaurus, its neck might have topped 16 meters–as long or longer than that of Supersaurus.

Now, I’m not saying that Sauroposeidon had a 16-meter neck. The conservative estimate is still 13 cervicals adding up to 11.5 meters. But the possibility of a longer neck is tantalizing, and can’t be ruled out based on current evidence. As usual, we need more fossils.

Happily, now that Sauroposeidon is known from Oklahoma, Texas, and Wyoming, and is one of the best-represented EKNApods instead of one of the scrappiest, the chances that we’ll find more of it–and recognize it–are looking good. I will keep my fingers firmly crossed–as they have been for the last 17 years.

* Radical pedantry note: of course we have very good evidence of sauropods getting more cervical vertebrae by recruiting dorsals into the cervical series. So, for example, 13 cervicals and 12 dorsals are supposed to be primitive for neosauropods, but diplodocids have 15 and 10, respectively–the obvious inference being that the first two dorsals got cervicalized. So in this narrow meristic sense, sauropods definitely did add cervicodorsals. But my point above is about the morphology of the verts themselves–once diplodocids had those two extra cervicals at the end, the former cervicodorsals were free to become more “cervicalized” in form. So effectively–in terms of the shapes of their necks–diplodocids added mid-cervicals.

References

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7 Responses to “The dark side of Sauroposeidon

  1. Mike Taylor Says:

    I love the sentence “The conservative estimate is still 13 cervicals adding up to 11.5 meters”.

  2. Nathan Myers Says:

    We’ve only found two articulated cervicals, so the conservative estimate of neck length is 2 to 3.5 meters. One might think sounds like plenty, and it would be if we were down-to-earth, sensible folk who race mounted giraffes vs. ostriches across the veldt. Based on other evidence, though, we expect even more cervicals will surface, allowing us to increase our estimate to as much as 11.5 meters, and conceivably more! This is wild speculation at this point, but that’s how we roll.

  3. Matt Wedel Says:

    We’ve only found two articulated cervicals, so the conservative estimate of neck length is 2 to 3.5 meters.

    Sorry, I’m having a slow morning. What are you talking about here? If it’s the Sauroposeidon holotype, OMNH 53062, we don’t have two articulated cervicals, we have four. Unless this is a joke that I am completely not getting–like I said, slow morning.

  4. Nathan Myers Says:

    So, ~5 meters, then, until more articulated verts show up. Yes, a joke, evidently not funny enough even with veldt racing. Just playing with shadings of “conservative”.

    BTW, Nicholls’s 2012-08-29 Sauroposeidon protelets reconstruction really cries out for a big puffball of a tail, maybe like Myrmecophaga tridactyla.

    BTBTW, Reference Wedel et al in 2008/7/24 goes to a link farm.

  5. djlivus Says:

    If Sauroposeidon was a basal titanosaurid, how this could affect its mass estimate of 40-60 tons (15% scaled-up brachiosaur)? And the estimated height.

  6. Mike Taylor Says:

    Titanosaurs are such a very broad group (they make up one third of all named sauropod genera) that you can’t really generalise about their proportions.

    But …in VERY broad generalities, brachiosaurs tend to have proportionally longer necks than most sauropods (including most titanosaurs) and titanosaurs tend to have proportionally larger torsos than most sauropods (including brachiosaurs). There are plenty of exceptions — e.g. the titanosaur Rapetosaurus has both a narrow torso and a long neck.

    If, and it’s a big if, Sauroposeidon conformed to “typical” titanosaur dimensions, then the consequences would be as follows.

    First, the neck-length estimates we have are based on actual vertebrae, so they’d stay much the same.

    Second, if the neck is proportionally shorter, then the rest of the animal is proportionally larger. So the torso would be larger than expected for a brachiosaur.

    Third, that torso would be a big bigger anyway, since it tends to be broad in titanosaurs.

    So putting it all together, we might speculate that a titanosaurian Sauroposeidon could be heavier than a brachiosaurian one. But all this is wildly wand-wavy, to the point where I wonder whether maybe I shouldn’t have said it at all.


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