Supersaurus, Ultrasaurus and Dystylosaurus in 2019, part 12: how big are the giant diplodocid bones in the Dry Mesa Quarry?

August 19, 2019

And so the series continues: part 9, part 10 and part 11 were not numbered as such, but that’s what they were, so I am picking up the numbering here with #12.

If you’ve been following along, you’ll remember that Matt and I are convinced that BYU 9024, the big cervical vertebra that has been referred to Supersaurus, actually belongs to a giant Barosaurus. If we’re right about, then it means one of two things: either Supersaurus synonymous with Barosaurus, or there are two diplodocids mixed up together.

Jensen (1987:figure 8c). A rare — maybe unique? — photograph of the right side of the big “Supersaurus” cervical vertebra BYU 9024. We assume this was taken before the jacket was flipped and the presently visible side prepped out. We’d love to find a better reproduction of this image.

Which is it? Well, seventeen years ago Curtice and Stadtman (2002:39) concluded that “all exceptionally large sauropod elements from the Dry Mesa Quarry can be referred to one of two individuals, one a Supersaurus and one a Brachiosaurus […] further strengthening the suggestion that all of the large diplodocid elements belong to a single individual.” It is certainly suggestive that, of all the material that has been referred to Supersaurus, there are no duplicate elements, but there are nice left-right pairs of scapulocoracoids and ischia.

But do all those elements actually belong to the same animal? One way to address that question is to look at their relative sizes and ask whether they fit together.

Sadly, when Matt and I were at BYU we didn’t get to spend time with most of these bones, but there are published and other measurements for a few of them. Jensen (1985:701) gives the total lengths of the two scapulocoracoids BYU 9025 and BYU 12962 as 2440 and 2700 mm respectively. Curtice et al. (1996:94) give the total height of the last dorsal BYU 9044 as 1330 mm. We have measured the big cervical BYU 9024 (probably C9) ourselves and found it to measure 1370 mm in total length. Finally, while there is no published measurement for the right ischium BYU 12949 (BYU 5503 of Jensen’s usage), we can calculate it from the scalebar accompanying Jensen’s illustration (with all the usual caveats) as being 1235 mm long.

Jensen (1985:figure 7a). BYU 12946 (BYU 5503 of his usage), the right ischium assigned to Supersaurus. By measuring the bone and the scalebar, we can calculate the length as 1235 mm.

Do these measurements go together? Since we’re considering the possibility of Supersaurus being a big Barosaurus, the best way to test this is to compare the sizes of the elements with the corresponding measurements for AMNH 6341, the best known Barosaurus specimen.

For this specimen, McIntosh (2005) gives 685 mm total length for C9, 901 mm total height for D9 (the last dorsal) and 873 mm for the ischia (he only provides one measurement which I assume covers both left and right elements). The scapulocoracoids are more complex: McIntosh gives 1300 mm along the curve for the scapulae, and 297 mm for the length of the coracoids. Assuming we can add them in a straight line, that gives 1597 mm for the full scapulocoracoid.

I’ve given separate measurements, and calculated separate ratios, for the left and right Supersaurus scapulocoracoids. So here’s how it all works out:

Specimen Element Size (mm) Baro (mm) Ratio Relative
9024 Mid-cervical vertebra 1370 685 2.00 124%
9044 Last dorsal vertebra 1330 901 1.48 92%
9025 Left scapulocoracoid 2440 1597 1.53 95%
12962 Right scapulocoracoid 2700 1597 1.69 105%
12946 Right ischium 1235 873 1.41 88%

The first five columns should be self-explanatory. The sixth, “proportion”, is a little subtler. The geometric mean of the size ratios (i.e. the fifth root of their product) is 1.6091, so in some sense the Dry Mesa diplodocid — if it’s a single animal — is 1.6 times as big in linear dimension as the AMNH 6341 Barosaurus. The last column shows each element’s size ratio divided by that average ratio, expressed as a percentage: so it shows how big each element is relative to a hypothetical isometrically upsized AMNH Barosaurus.

As you can see, the cervical is big: nearly a quarter bigger than it should be in an upscaled Barosaurus. The two scaps straddle the expected size, one 5% bigger and the other 5% smaller. And the dorsal and ischium are both about 10% smaller than we’d expect.

Can these elements belong to the same animal? Maaaybe. We would expect the neck to grow with positive allometry (Parrish 2006), so it would be proportionally longer in a large individual — but 25% is a stretch (literally!). And it also seems as though the back end of the animal (as represented by the last dorsal and ischium) is growing with negative allometry.

A nice simple explanation would be that that all the elements are Supersaurus and that’s just what Supersaurus is like: super-long neck, forequarters proportionally larger than hindquarters, perhaps in a slightly more convergent-on-brachiosaurs way. That would work just fine were it were not that we’re convinced that big cervical is Barosaurus.

Here’s how that would look, if the BYU Supersaurus is a large Barosaurus with different proportions due to allometry. First, Scott Hartman’s Barosaurus reconstruction as he created it:

And here’s my crudely tweaked version with the neck enlarged 24% and the hindquarters (from mid-torso back) reduced 10%:

Does this look credible? Hmm. I’m not sure. Probably not.

So: what if we’re wrong?

We have to consider the possibility that Matt and I misinterpreted the serial position of BYU 9024. If instead of being C9 it were C14 (the longest cervical in Barosaurus) then the AMNH analogue would be 865 mm rather than 685 mm. That would make it “only” 1.58 times as long as the corresponding AMNH vertebra, which is only 3% longer than we’d expect based on a recalculated geometric mean scale of 1.5358 — easily within the bounds of allometry. We really really really don’t think BYU 9024 is a C14 — but it’s not impossible that its true position lies somewhere posterior of C9, which would mean that the allometric interpretation would become more tenable, and we could conclude that all these bones do belong to a single animal after all.

Of course, that would still leave the question of why the Supersaurus scapulocoracoids are 10% bigger than we’d expect relative to the last dorsal vertebra and the ischium. One possible explanation would be to do with preparation. As Dale McInnes explained, there’s some interpretation involved in preparing scaps: the thin, fragile distal ends shade into the cartilaginous suprascapula, and it’s at least possible that whoever prepped the AMNH 6341 scaps drew the line in a different place from Dale and his colleagues, so that the Barosaurus scaps as prepared are artificially short.

Putting it all together: it might easily be the case that all the elements really do belong to a single big diplodocid individual, provided that the big cervicals is more posterior than we thought and the AMNH scaps were over-enthusiastically prepped.

References

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10 Responses to “Supersaurus, Ultrasaurus and Dystylosaurus in 2019, part 12: how big are the giant diplodocid bones in the Dry Mesa Quarry?”


  1. It’s interesting to note that if BYU 9024 is a C12, which seems eminently more reasonable than C14, it has about the same proportion to AMNH 6341 as the right scapulocoracoid. The ischium size issue could just be the vagaries of scale bars and three-dimensional structure, and BYU 9044 has a proportionally shorter neural spine than AMNH 6341, so you’d expect its total height to seem a bit small. Going off of your photo of BYU 9044 and using the vertebra height as a scale bar, I get a centrum width of 460 mm for a size ratio of 1.69, which just about lines up with the right scapulocoracoid and BYU 9024-as-C12.

    However, you guys have opened my eyes to a bold new world of multiple giant diplodocids at the Dry Mesa quarry. If BYU 9024 is as Barosaurus-like as you say—I’ll take your word on it, cervical vertebrae aren’t really my thing—none of the other elements really show it. The scapulocoracoid still seems like it might be rather Brontosaurus-like.The suprascapula issue has me concerned though, as it could cast doubt on some of the characters I’ve discussed if it really is that subjective—as well as the utility of some widely-used phylogenetic characters in general!

  2. Matt Wedel Says:

    I think anything within 10% can safely be assumed to be consistent with a single animal, because these things vary a lot among individuals and species. Why do I think this? The big mounted apatosaurs at the Carnegie Museum (CM 3018, Apatosaurus louisae), University of Wyoming (UWGM 15556, formerly CM 563, Brontosaurus parvus), and the Field Museum (FMNH P25112, Apatosaurinae indet.) all have femora right around 180cm long, but their first caudal vertebrae vary in diameter by about 25% (see this post for documentation).

    With that in mind, and given that neither the Lovelace et al. (2008) analysis nor the Tschopp et al. (2015) analysis puts Supersaurus anywhere near Barosaurus in the phylogeny, applying Barosaurus proportions to decide what bits go together with Supersaurus is pretty suspect.

    I have no problem with the scaps and pelvic elements going in the same animal. The length difference between the Baro and Super scaps is more likely to be from different degrees of ossification of the cartilaginous end-plate, than from preparation. No decent preparator is going to knock off cm of bone just because it’s thin.

    With all that said, the cervical still looks too big. Although I am troubled by the fact that according to the quarry map, it came from right between the Supersaurus scap-coracoids. Still, the quarry was a jumble, so who knows.

    I am extremely unmoved by the argument that all of the big diplodocoid material in the quarry has to belong to one individual. That’s certainly not true of the brachiosaur material — the big “Ultrasauros” scap-coracoid is from a much larger individual than the presacrals from the same quarry (like BYU 12866 and 12867, see this post and this one, respectively). If a giant brachiosaurid individual can be represented in the quarry by a single element, then it’s no more of a stretch to accept that a giant Barosaurus could be as well.

  3. LeeB. Says:

    Weren’t there some tail vertebra from the Dry Mesa quarry that don’t belong to Supersaurus but some other Diplodocid?
    From memory I think that this had been reported.
    Also if the neck vertebrae was from a gigantic Barosaurus then I wonder what this is saying about the living conditions for sauropods at the time that produced several super giants.

  4. Matt Wedel Says:

    Oh, yeah, there are loads of other sauropods in Dry Mesa, including IIRC both Diplodocus and Barosaurus, just not huge individuals. Brian Curtice and Ray Wilhite wrote a paper about the diversity of dino in Dry Mesa based on caudal elements. I have a hardcopy of it entombed somewhere within my office. If I ever rediscover it, I’ll scan it and pass it around. But it would probably be faster to just ask Ray if he has a copy, so I’m going to do that right now. Keep you posted!

    Re: the multiple giant sauropods, there was already at least one giant diplodocoid and one giant brachiosaurid. Although I wonder if it wasn’t an unusual environment so much as an unusually productive quarry. If every Morrison quarry produced as much material as Dry Mesa, maybe more of them would record the presumably-rare giant individuals.

  5. Teddy Says:

    How long is centrum 9044 ?centrum dorsal 9 is 27 cm long

  6. Mike Taylor Says:

    The centrum of the “Ultrasaurus” type dorsal BYU 9044 is 500 mm long (Curtice et al. 1996:table 2), but they think that is largely due to crushing and that an “uncrushed” centrum would be 400 mm long. For what little it’s worth (they have spent waaay more time with the bone than I have) I tend to be sceptical about that, because they think the additional length arose because “extensize transverse and oblique crushing artificially elongate the centrum and exaggerate the anterior ball” (p90) and I can’t envisage a form of crushing that would do that: take a look at the photo here and see what you think.

    What happens when we compare these values with those for the AMNH Barosaurus?, I hear you ask! McIntosh (2005:50) gives D9 lengths of 270 max and 215 without ball. Since these numbers suggest the condyle of the AMNH D9 makes up 20 of the centrum length, the honest thing to do is probably to also take the condyle of the “Ultrasaurus” dorsal at face value, which means its length exceeds that of Barosaurus by 500/270 = a factor of 1.85: noticeably more than the 1.48 ratio between their heights. That means the vertebra is 1.85/1.48 = 1.25 times as long as we’d expect a Barosaurus dorsal that tall to be. Interesting! (If we use Curtice et al.’s “uncrushed” length of 400 mm, it comes out 1.48 times as long as in Barosaurus, which is exactly the same as the ratio between their heights — but I think it’s special pleading to allow Barosaurus a condyle but not allow one to “Ultrasaurus”.)

  7. Mike Taylor Says:

    Sorry I missed this earlier: Matt wrote:

    Given that neither the Lovelace et al. (2008) analysis nor the Tschopp et al. (2015) analysis puts Supersaurus anywhere near Barosaurus in the phylogeny, applying Barosaurus proportions to decide what bits go together with Supersaurus is pretty suspect.

    To be clear: what I am trying to do in this post is to test whether the sizes of elements allow the interpretation that they are all from a single individual of Barosaurus specifically — not to assume up front that Supersaurus is proportioned like Barosaurus and then ask whether all the elements can belong to a single individual of that, whatever it is.

  8. Teddy Says:

    Thank you very much for your reply.
    On the test for pictures and sketches,l think the lengtn without ball of dorsal byu 9044 is 395 mm. This is 1,83 the length dorsal 9 of barosaurus ,but 1,68 the length dorsal 8 of barosaurus amnh6341r

  9. aiden Says:

    how much do the vertebral columns weigh?

  10. Mike Taylor Says:

    I don’t know at all, and I doubt anyone does. Great question.


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