Supersaurus, Ultrasaurus and Dystylosaurus in 2019, part 8: we finally get to Ultrasauros!

July 9, 2019

One of the strange things about Jensen’s 1985 paper is that the abstract implies that he informally considered the Ultrasauros scapulocoracoid to be the type specimen.

Cast of BYU 9462, scapulocoracoid referred to Ultrasaurus macintoshi (possibly intended to the be the holotype), at Brigham Young Museum. This photo is one of a series in which I turned the cast in place to obtain photos for a photogrammetric model.

Here’s what Jensen (1985:697) says:

From 1972 to 1982 three exceptionally large sauropod scapulocoracoids […] were collected from the base of the Brushy Basin Member of the Upper Jurassic, Morrison Formation, in western Colorado. Two of the scapulae are conspecific, but the third represents a second genus and possibly a new family. The two conspecific specimens are described here as Supersaurus vivianae; the second genus is described as Ultrasaurus mcintoshi.

But on page 704, he formally and unambiguously nominated the dorsal vertebra as the holotype:

Family Brachiosauridae
Ultrasaurus macintoshi, n. gen., n. sp.
[…]
Holotype.—BYU 5000, posterior dorsal vertebra.
Referred material.—BYU 5001, scapulocoracoid.

Stranger still, two years after this, Jensen (1987:603) straight up claimed – quite incorectly — that the scap was the Ultrasaurus holotype:

In 1979 a scapulocoracoid, 2.70 m (8’10”) long (Figs. 6A-B, 9I) was collected in the Dry Mesa Quarry. This scapula, BYU 5000 [sic; he meant BYU 5001], is readily referrable to the Brachiosauridae (Fig. 9H) and is the holotype of Ultrasaurus macintoshi Jensen, 1985.

But it sayin’ it’s so don’t make it so. The joint evidence of the 1985 abstract and the 1987 extract suggest that Jensen probably intended the scap to be the holotype and somehow accidentally designated the wrong element — or was persuaded to do so against his own judgement. But however it came about, the scap is not the holotype.

BYU 9462, the scapulocoracoid referred by Jensen to Ultrasauros. Mike Taylor for scale, doing a Jensen. Note that the actual specimen is very much a mosaic of bone fragments, rather than the solid, complete bone that the cast might suggest.

Instead, the holotype remains the large posterior dorsal vertebra BYU 9044 (BYU 5000 of Jensen’s usage) which Curtice et al. (1996) convincingly showed to be diplodocid, and referred to Supersaurus, making Ultrasaurus (and its subsequent replacement Ultrasauros) a junior synonym of that name.

Ultrasauros macintoshi holotype dorsal vertebra BYU 9044, in left lateral view, photographed at the North American Museum of Natural Life. Sorry about all the reflections off the glass case.

But wait, wait. We’ve shown that there are probably two big diplodocids in the Dry Mesa quarry: Barosaurus (represented by the big cervical BYU 9024) and something different (represented by the “Dystylosaurus” dorsal, BYU 4503). The Ultrasauros holotype vertebra probably belongs to one of these (unless there are three big diplodocids in there but we’ll ignore that possibility). But we can’t tell whether the Ultrasauros dorsal belongs with the Barosaurus cervical or the Dystylosaurus dorsal.

All of this means that Ultrasauros is a synonym, but we don’t know of what. It might be Barosaurus; it might be Supersaurus, whatever that is, if it’s not a nomen dubium; and it might be Dystylosaurus, if Supersaurus is a nomen dubium. Yikes.

Well, then. Is it Barosaurus? Here are the dorsal vertebrae of the fairly complete AMNH specimen, in a composite that I put together a few years ago from McIntosh’s (2005) illustrations:

Barosaurus lentus AMNH 6341 dorsal vertebrae 1 to 9 in anterior, left lateral and posterior views. Modified from McIntosh (2005:figure 2.5)

We can compare these with the photo above of the Ultrasauros dorsal in left lateral view, and with this one in posterior view:

Ultrasauros macintoshi holotype dorsal vertebra BYU 9044, in posterior view, photographed at the North American Museum of Natural Life. Sorry about all the reflections off the glass case.

I wouldn’t want to hang too much on those poor quality, postage-stamp-sized monochrome photos of the Barosaurus dorsals. And I’m also more than aware of the imperfections in my photos of the “Ultrasauros” dorsal. But to the naked eye, there’s nothing here that immediately screams they couldn’t be the same thing.

Lull’s (1919) monograph on the original Barosaurus specimen YPM 429 also illustrated a posterior dorsal, which he designated D9. Lull helpfully provided both drawings and photographs:

Lull (1919: plate IV: parts 4-6). Barosaurus lentus holoype YPM 429, 9th dorsal vertebra in anterior, right lateral and posterior views (line drawing).

Lull (1919: plate IV: parts 4-6). Barosaurus lentus holoype YPM 429, 9th dorsal vertebra in anterior, right lateral and posterior views (photographs).

With something a bit more substantial to go on, the case for the Ultrasaurus vertebra being Barosarus doesn’t look so good.

Most obviously, its centrum is much longer than that of the Barosaurus dorsal — and indeed, than any posterior dorsal vertebra of any diplodocid. This character is the reason — the only reason — that Jensen (1985:704) initially thought it was brachiosaurid: “Ultrasaurus shares the family characteristic of a long dorsal centrum with Brachiosaurus, but in other features it has no parallel with that genus”. Curtice et al. (1996:90) argued that “extensive transverse and oblique crushing artificially elongate the centrum […]. Without the crushing […] the centrum shrinks considerably in length”. Based on my photos, I can’t really see any justification for this claim, but Curtice spent waaay more time with this specimen than I have done, so I’m going to hold that observation lightly.

But there are other features of BYU 9044 that are not a good match for Lull’s illustrations. These include a less robust looking and more prominently laminated subzygapophyseal neural arch, and a neural spine that is anteroposteriorly broader but transversely narrower than in Lull’s specimen. Also, the apex of the neural spine in anterior or posterior view is convex in BYU 9044 but concave in YPM 429.

None of these characters can be considered to definitely separate BYU 9044 from Barosaurus, especially in light of that element’s crushing, the imperfect preservation of Lull’s specimen, the possibility of serial variation, and the fact that I am working only from photographs and drawings of both. But when you put all the differences together, they combine to at least suggest that Ultrasaurus is not Barosaurus — and that it is therefore most likely Supersaurus/Dystylosaurus.

So what about the scapulocoracoid?

It looks brachiosaurid, as Jensen observed. Curtice et al. (1996) concurred, and referred it to Brachiosaurus sp. In fact, when compared with the best-preserved scapula of a known brachiosaurid Giraffatitan HMN Sa 9), it’s not all that similar:

Brachiosaurid scapulocoracoids. Left: cast of BYU 9462, right scapulocoracoid referred to Ultrasauros macintoshi, at Brigham Young Museum, with Mike Taylor for scale. Right: HMN Sa 9, left scapula only (coracoid is not co-ossified) of Giraffatitan brancai, scaled to same blade length as BYU 9462, photo by FunkMonk (Michael B. H.), CC By-SA.

It’s apparent, when looking at the two scaps together, that there are significant differences: BYU 9462 is in every respect less robust, having a less expanded distal blade, a more constricted midshaft, a less promiment and narrower acromial ridge and a much less robust ventral ridge. In addition, the acromion process is hooked in Sa 9, so that its tip projects laterally, whereas it is rounded in BYU 9462. Finally, the shapes of the distal blades differ, having a gently rounded profile in BYU 9462 but a distinct kink in Sa 9 where the dorsal part of the margin inclines anterodorsally.

What does all this mean? We don’t know. I’m certainly not arguing that BYU 9462 is not brachiosaurid, as it does seem to differ less from Giraffatitan scapulae than from those of other sauropods. All I’m saying is that it’s not all that Giraffatitan-like. But then every bone that we know from both Giraffatitan and Brachiosaurus is significantly different between them (Taylor 2009:798), so if a subsequently discovered associated skeleton one day shows us that this is just what the scapulocoracoid of Brachiosaurus altithorax looks like, it would not be a huge shock.

Still, as things stand, I’m not really convinced that the referral to Brachiosaurus sp. — based on a not-particularly-close resemblance to a completely different brachiosaurid — is rock solid. Had the scap been the type specimen, as Jensen probably intended, I would consider that the sound move would be to continue to consider Ultrasauros as a distinct taxon from Brachiosaurus, unless and until an associated specimen demonstrates that synonymy is warranted.

But that’s all in Shoulda-Coulda-Woulda territory. In fact the scapulocoracoid is not the type specimen, and so the name Ultrasauros remains sunk, even though we can’t tell whether it’s a synonym of Barosaurus, Supersaurus or Dystylosaurus. That will remain the case unless someone takes the initiative to raise a new name for the scapulocoracoid — which we can, at least, be confident does not belong the diplodocid Ultrasauros. I think that would be a reasonable move for someone to make, but it’s not one that I feel moved to make myself.

… and with that, I think we have finally reached the end of this series. We may revisit it in the future to say more about Jimbo, or maybe Dinheirosaurus, but this series has been the substance of what we have to say. Hope you’ve enjoyed it!

References

 

 

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13 Responses to “Supersaurus, Ultrasaurus and Dystylosaurus in 2019, part 8: we finally get to Ultrasauros!”

  1. LeeB Says:

    You definitely need more material described of North American Brachiosaurus.
    Do you know how many skeletons of it have been found and are any of them awaiting description?”

    LeeB.

  2. Mike Taylor Says:

    I think Matt’s more up to speed on that than I am. I’ll await his reply.


  3. Well, this has been an interesting series of posts! Very informative and interesting.

    Goodness, that is a gracile scapula—offhand, it strikes me as one of the most gracile scapulae of any sauropod, assuming Jensen put it back together right.

    One more feature that may distinguish “Ultrasaurus” and Giraffatitan is the ventral margin of the scapula. It’s entirely straight in Giraffatitan, but in “Ultrasaurus” it curves ventrally towards the distal end. I wouldn’t put too much stock into this, though, as one Giraffatitan specimen (Ki 74) appears to be curved ventrally too.

    I also note that Jensen has reconstructed BYU 9462 with a notch taken out of the anterodorsal corner of the coracoid—something that you, Mike, noted in both Brachiosaurus and Giraffatitan. Assuming that none of that is due to breakage, it’s a promising brachiosaurid synapomorphy for “Ultrasaurus.” Other than that, though, BYU 9462 doesn’t seem to be quite a match for the Brachiosaurus holotype.

    It’s worth noting that at least one other possible Brachiosaurus scapula has been described—the juvenile SMA 0009. Overall, the scapula mostly looks like it could plausibly be a juvenile of the same species as BYU 9462, although it does have a ‘hooked’ acromion.

    The apex of the neural spine being convex in Ultrasauros meshes nicely with Dystylosaurus’s lack of bifurcation in the more anterior dorsals, so that works with their probable synonymy. Is it just me or does YPM 429 have enormous aliform processes that aren’t present in AMNH 6341?

    It’s so weird that Jensen made the vertebra the type specimen and not the scapula. At least the vertebra being the holotype lets us avoid the situation of Ultrasaurus probably being a synonym of Brachiosaurus but it not being provable.

  4. TimW Says:

    Mike – I admire your restraint in not raising a new name for the brachiosaurid scap. As you say, it would be an entirely reasonable thing to do, and you would be fully entitled to do so.

    As you would know, D’Emic & Carrano (2019) believed that the available material is consistent with the presence of only one brachiosaurid species in the Late Jurassic of North America: B. altithorax. Their exact words were:

    “We argue that these elements [skull, etc] are most parsimoniously referred to B. altithorax. Including these tentatively referred elements in a phylogenetic analysis does not alter the hypothesized relationships of B. altithorax, congruent with the presence of a single brachiosaurid taxon across western North America in the Late Jurassic.”

    So, on that basis alone, the most parsimonious approach would be to regard the Dry Mesa scap as belonging to B. altithorax, until proven otherwise (e.g., if evidence of another brachiosaurid shows up in the Morrison Fm).

    However, two things… First, D’Emic & Carrano did not mention the Ultrasaurus scap specifically. Second, I can foresee some folks taking issue with the approach of pooling all Morrison brachiosaurid material into one taxon, considering the lack of overlapping material in some cases. As the authors say “some degree of individual research preference and argumentation is unavoidable in such situations”.

  5. Matt Wedel Says:

    Mike wrote:

    Had the scap been the type specimen, as Jensen probably intended, I would consider that the sound move would be to continue to consider Ultrasauros as a distinct taxon from Brachiosaurus, unless and until an associated specimen demonstrates that synonymy is warranted.

    I don’t think synonymy is warranted, at least at the species level, based on the very different shapes of the coracoids. The fairly square Ultrasauros coracoid is quite different from the oblong Brachiosaurus altithorax coracoid.

    John wrote:

    Goodness, that is a gracile scapula—offhand, it strikes me as one of the most gracile scapulae of any sauropod, assuming Jensen put it back together right.

    I think there are photos of the Ultrasauros scap in the field showing that the put-back-together version is essentially correct.

    Lee wrote:

    You definitely need more material described of North American Brachiosaurus. Do you know how many skeletons of it have been found and are any of them awaiting description?

    Yes, I do know how many: zero. That said, there are some bits and bobs here and there that have not been described, including some material not covered by D’Emic & Carrano (2019). Most of that additional Brachiosaurus (or at least brachiosaurid) material is covered in a table in Bonnan and Wedel (2004, available here). Since 2004 there hasn’t been a lot of new stuff. There’s the big pes described by Maltese et al. almost exactly one year ago (here), a humerus from the “Gnatalie” quarry that is on display at the LACM (pictured in this post), aaaand something fairly exciting that I can’t tell you about just yet. Watch this space.

  6. UriWolk Says:

    Wow, that was a really great post series. I read straight through all of them, and they just kept coming (which is always great!). Terrific job.

    In light of all the information you’ve covered (in great and clear detail), I’m left with one question: What do you think are the chances this will materialise to a technical paper any time soon? Whether it’s about searching for autapomorphies or character combinations in Supersaurus, or reviewing the state of things as they stand today just like you did in this series. All of this really seems fitting of such a description to me, but of course it depends on your availability and will to do so, other research projects at hand, etc…

    I must also say, John D’Angelo’s comments on previous posts about possible diagnostic characters seem like a good head start to re-diagnose the type.

  7. Mike Taylor Says:

    Thanks, UriWolk! As you probably guessed, the plan is to convert this series of posts into a preprint as quickly as we conveniently can, and to submit it as a manuscript for peer-review at the same time. We have a habit of letting papers expand into monsters, so I will aim with this one to keep it constrained: just a review of what we know now and what the options are. That leaves the path open for us, or someone else, to write a subsequent paper proposing a rediagnosis, some nomenclatural acts, or whatever seems appropriate.

  8. LeeB Says:

    Hmm the small nearly complete Brachiosaur from the Wyoming quarry that the foot was found in sounds interesting…

    LeeB.

  9. Matt Wedel Says:

    Hmm the small nearly complete Brachiosaur from the Wyoming quarry that the foot was found in sounds interesting…

    Doesn’t it? Unfortunately, I fear that specimen may have been effectively lost to science. Keeping in mind that everything I know about it comes from a couple of conversations at SVP more than a decade and a half ago, my therefore-possibly-flawed understanding is that it was sold (or possibly gifted or otherwise transferred) to a museum in South Korea, where it was prepared so inexpertly that the neural arches were prepped right off the cervical centra. I don’t know which museum it went to, and I don’t know if it ever went on display, but I am nearly certain that it’s never been described (and if it has been described, that publication must be truly obscure).

    Keep in mind that’s all hearsay and I’m not trying to slag off any people or institutions, just relaying everything I’ve heard on the topic in the hopes that someone more knowledgeable will show up and correct me.

  10. LeeB. Says:

    Sometimes people can really piss you off.
    If you run a museum and buy a unique specimen that should only be the beginning; you should hire preparators that know what they are doing and then you should publish a paper on it.
    The number of destroyed specimens is appalling and also the number of really good informative specimens sitting in museums undescribed; putting specimens in cases high up on walls where they are totally inaccessible doesn’t help either.
    LeeB.

    (Pardon my rant).


  11. Matt:
    I don’t think synonymy is warranted, at least at the species level, based on the very different shapes of the coracoids. The fairly square Ultrasauros coracoid is quite different from the oblong Brachiosaurus altithorax coracoid.

    Agreed. One character is, of course, always a weak basis for separating species, but the shape of the “Ultrasaurus” coracoid and the Brachiosaurus altithorax holotype coracoid do look pretty different. My wild and unfounded guess is that it’s most likely the same Brachiosaurus lineage sampled at two different points in time.

    I think there are photos of the Ultrasauros scap in the field showing that the put-back-together version is essentially correct.

    I suspected as much, but it’s good to have that corroborated. Incidentally, I’ve been assuming that pretty much the same is likely the case for the triangular process on the ventral margin of Supersaurus Scap A, as Jensen illustrates it with one but it is apparently not present on the actual fossil nowadays. It would be good to have confirmation if anyone’s seen a relevant photo!

    UriWolk:
    I must also say, John D’Angelo’s comments on previous posts about possible diagnostic characters seem like a good head start to re-diagnose the type.

    I’m glad that my comments on the issue seem to have generally been fairly well-received!

  12. Ronald Says:

    Very interesting series of posts (and long overdue)!
    Pity that not everything is clear and unambiguous now, but such is life and taxonomy.

    Would it be an idea to summarize everything discussed in some handy way? What I had in mind (but just ignore it if you find it a stupid idea) is some kind of cross-table or matrix, with all relevant specimens (original ID, present ID), their nature (scapula, cervical etc.), original taxonomic designation (e.g. Ultrasaurus etc.), present preferred designation (e.g. Barosaurus etc.).

    Question: after this series of posts, have ideas changed with regard to the size of Barosaurus (https://svpow.com/2016/09/16/how-horrifying-was-the-neck-of-barosaurus/), I mean in view of possible new Barosaurus material?

  13. Mike Taylor Says:

    I have a post in the works that is more or less along the lines you suggest.

    That older post on the size of Barosaurus was based on precisely the work that this series of posts has laid out.


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