I had an interesting opportunity when I was in Utah and Colorado a couple of weeks ago. At Dinosaur Journey in Fruita, Colorado, I went looking for a cast of the Potter Creek Brachiosaurus humerus. I found it — more on that another time — and I also found a cast of BYU 4503, the holotype dorsal vertebra of Dystylosaurus (now almost universally regarded as Supersaurus [but then…]), lurking with it in a corner of the collections room.

Dystylosaurus cast, posterior view.

Somehow I had overlooked the Dystylosaurus cast on all of my previous visits to DJ, which is a shame, because the cast is easy to pick up, flip over, and manipulate. Very much unlike the actual fossil, which combines the charming attributes, shared with many other sauropod vertebrae, of weighing hundreds of pounds but still being awfully fragile.

Dystylosaurus cast, anterior view.

So, hey ya, I had a chance to photograph and measure both sides of the vertebra. You’re not supposed to take measurements from casts, but I figured what the heck, no-one was going to lock me up for it, and I could compare the measurements from the cast to the measurements of the real thing when I visited BYU later in the trip. And that’s exactly what I did. It was easy to make sure I took the second set of measurements the same way I had done the first set, because I took them just a few days apart.

The real deal at BYU.

Here’s what I got. For each measurement, the actual value measured from the real fossil at BYU comes first, followed by the same measurement from the cast at Dinosaur Journey, followed by the difference as a percentage of the first (true) measurement.

  • Total Height (as preserved): 1050mm / 1022mm / -2.6%
  • Max Width (as preserved): 905mm / 889mm / -1.8%
  • Anterior Centrum Height: 400mm / 394mm / -1.5%
  • Anterior Centrum Width: 470mm / 454mm / -3.4%
  • Posterior Centrum Height: 365mm / 352mm / -3.5%
  • Posterior Centrum Width: 480mm / 473mm / -1.5%

They’re not the same! On average, the measurements of the cast are 2.4% smaller than the same measurements taken from the actual bone. (Incidentally, you may be wondering how I measured the posterior centrum faces of the BYU vertebra without flipping it. I used a couple of wooden blocks as orthogonators and measured between them, and I did it at several points to make sure they were truly parallel. In essence, I made giant redneck calipers, a method that Mike and I have had to employ many times when measuring huge, weirdly-shaped fossils. Remind me to show you John Foster’s giant caliper setup sometime.)

Dinosaur Journey cast in right lateral view, big doofus for scale.

Anyway, the discrepancy in the measurements should not be surprising. It is a known phenomenon that when an object is molded and cast, there is a little bit of shrinkage. You can see it bedevil Adam Savage in his quest for the ultimate Maltese Falcon replica in this charming video:

So, on one hand, no outright disasters here; all of the cast measurements are within a few percent of the real measurements, so if all you had was a cast, you could get a pretty good sense of the size of the real thing. But precision counts, even among giant sauropods. In a world where the largest vertebra of Argentinosaurus is only 1cm bigger in diameter than the largest vertebra of Patagotitan, differences like I got with Dystylosaurus would be enough to scramble the order of giant vertebrae. So if you’re ever stuck measuring something from a cast, be forthright and say as much, so that no-one mistakes the cast measurements for the real thing.

Here are some more measurements from BYU 4503, the real thing, for you completists. Note that the vertebra is sheared a bit from right postero-ventral to left antero-dorsal, so figuring out how to take the centrum length is not straightforward. I ended up doing it twice, once orthogonal to the posterior centrum face, and once following the slant of the centrum, both at the mid-height of the centrum, as shown in the little diagram from my notebook (above).

  • Centrum Length, left side, orthogonal: 295mm
  • Centrum Length, left side, on the slant: 310mm
  • Centrum Length, right side, orthogonal: 280mm
  • Centrum Length, right side, on the slant: 305mm
  • Max Width across prezygs: 305mm
  • Min gap between prezygs: 19mm
  • Max Width across parapophyses: 620mm
  • Max antero-posterior length of prezyg articular surfaces: 55mm
  • Max antero-posterior depth of hypantrum: 95mm
  • Max antero-posterior depth of fossa between spino-prezyg laminae (SPRLs): 80mm
  • Neural spine cavity, max antero-posterior extent: 40mm
  • Neural spine cavity, max medio-lateral extent: 70mm

Finally, a huge thanks to Julia McHugh at Dinosaur Journey and Brooks Britt and Rod Scheetz at BYU for letting me come play with their huge toys er, hugely important scientific specimens. Rod was particularly helpful, shifting giant things about with a forklift, helping me measure bones that are longer than I am tall, and boxing up loan specimens for me. Mike and I have had really good luck with pro-science curators and collections managers, but the folks at DJ and BYU have always been standouts, and I can’t thank them enough.

Back into the Corner of Shame, artificially tiny Dystylosaurus!

This awesome photo was taken in the SVPCA 2019 exhibit area by Dean Lomax (L). On the right, Jessie Atterholt, me, and Mike are checking out some Isle of Wight rebbachisaurid vertebrae prepped by Mick Green, who is juuuust visible behind Dean. Jessie’s holding a biggish (as rebbachisaurids go) dorsal or caudal centrum and partial arch, me a lovely little cervical, and Mike an astonishingly delicate and beautiful dorsal. You can see behind us more tables full of awesome fossils, and there were more still across the way, behind Dean and Mick. I was going to throw this photo into the last post to illustrate the exhibit area, but by the time the caption had hit three lines long, I realized it needed a post of its own.

Photo courtesy of Dean, and used with permission. Mark your calendars: on Sunday, Oct. 13, Dean will be speaking at TEDx Doncaster, with a talk titled, “My unorthodox path to success: how my passion for the past shaped my future”. You can follow the rest of Dean’s gradual conquest of the paleosphere through his website, http://www.deanrlomax.co.uk/.

My talk (Taylor and Wedel 2019) from this year’s SVPCA is up!

The talks were not recorded live (at least, if they were, it’s a closely guarded secret). But while it was fresh in my mind, I did a screencast of my own, and posted it on YouTube (CC By). I had to learn how to do this for my 1PVC presentation on vertebral orientation, and it’s surprisingly straightforward on a Mac, so I’ve struck while the iron is hot.

For the conference, I spoke very quickly and omitted some details to squeeze the talk into a 20-minute slot. In this version, I go a bit slower and make some effort to ensure it’s intelligible to an intelligent layman. That’s why it runs closer to half an hour. I hope you’ll find it worth your time.

References

We’re just back from an excellent SVPCA on the Isle of Wight. We’ll write more about it, but this time I just want to draw attention to a neat find. During a bit of down time, Matt and Vicki were wandering around West Cowes (the town where the scientific sessions were held), when they stumbled across a place called That Shop. Intrigued by all the Lego figures in the window, they went in, and Matt found a small section of fossils. Including … an Iguanodon pelvis, supposedly certified as such by the Dinosaur Isle museum.

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Here it is: I imagine that whoever classified it read this elongate concave surface as part of the acetabulum. Matt’s hypothesis is that they mistook it for a sacral vertebra and that became “pelvis” via over-simplification.

It’s about 18 cm in a straight line across the widest part, or 20 cm around the curve.

Here is an actual documentary record of Matt’s moment of discovery:

Yep, you got it! It’s a sauropod vertebra! (Matt would never have spent good money on a stinkin’ appendicular element of a stinkin’ ornithopod.)

Specifically, it’s the bottom half of the front part of the centrum of a dorsal vertebra:

Eucamerotus” dorsal vertebra NHMUK PV R88 in right lateral and anterior views. Non-faded portions show the location of the Wedel Specimen. Modified from Hulke (1880: plate IV).

In these photos, we’re looking down into it more or less directly dorsal view, with anterior to the left. Click through the photos, and — once you know what you’re looking at — you can clearly see the pneumatic spaces: nice patches of finished bone lining the camellae, with trabecular bone in between.

Clearly there’s nowhere near enough of this to say what it is with any certainty. But our best guess is that it seems compatible with a titanosauriform identity, quite possibly in same space as the various Wealden sauropod dorsals that have been assigned to Ornithopsis or Eucamerotus.

References

  • Hulke, J. W.  1880.  Supplementary Note on the Vertebræ of Ornithopsis, Seeley, = Eucamerotous, Hulke. Quarterly Journal of the Geological Society 36:31–35.  doi:10.1144/GSL.JGS.1880.036.01-04.06

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

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

 

 

Poor Dystylosaurus. Always the bridesmaid. No-one seems to care much about it, yet the one and only vertebra that bears that name is the single most diagnostic elements out of all the individual bones that have been assigned to Supersaurus over the years.

A nice drawing of the “Dystylosaurus” dorsal vertebra in anterior and right lateral views. It’s probably Tracey Ford’s work (awaiting confirmation), from the PaleoFile page on Supersaurus.

Unfortunately, we weren’t able to learn a whole ton about this vertebra on the Sauropocalypse visit. We did see it, but it was flat on its back on a shelf not much taller than the anteroposterior length of the bone itself, so we weren’t able to get a good look at it in anything but dorsal and ventral views. If we’d had more time to get things arranged, I’m sure the BYU people would have been happy to get it down from the shelf for us, but we simply had so much to do in their collections that time was never made for it.

BYU 4503, the holotype and only element of Dystylosaurus edwini, an anterior dorsal vertebra. here seen in approximately dorsal view with anterior to the top. Matt Wedel for scale.

Matt actually got some rather better photos a few years ago, though (based on his comment on that post), there are probably no more than the couple in that old blog-post. (By the way, notice how very different the colour of the bone appears in Matt’s old photos from how it appears in my more recent one above.)

Why do I say so confidently that the Dystylosaurus vertebra is diagnosable? Because it has a whole suite of characters that tell us it’s an anterior dorsal vertebra from a diplodocid (dual centroprezygapophyseal laminae, anteroposteriorly compressed spine composed primarily of spinozygapophyseal rather than spinodiapophyseal laminae, drooping transverse processes), yet two features of the spine are never seen in such vertebrae: the spine is wholly unsplit without even a hint of bifurcation, even featuring macronarian-like lateral apices; and it’s hollow inside rather than being constructed from intersecting plates of bone. (You can see the internal hollow in the photo above.)

So what happens to its genus name given the doubts about Supersaurus‘s diagnosability? The general trend of comments on these posts has been that Supersaurus should stand or fall on its holotype, and I am inclined to agree that parachuting in the Dystylosaurus vertebra or Jimbo as a neotype to save the name would be a mistake. For one thing, despite its numerous appearances in kids’ books, the name Supersaurus is not that important in the technical literature: for example, no-one has named a clade Supersaurinae or similar. For another, the holotypic scapulocoracoid BYU 9025 is only questionably undiagnosable. There would always be the possibility that if someone nominated a neotype and wrestled it through the ICZN petition process, someone else would find a good solid way to diagnose the original holotype. That would be embarrassing.

The rare ventral-ish view of the Dystylosaurus dorsal vertebra BYU 4503. Sorry it’s not better. I do have 93 photos of it in this shelf, all of them individually pretty terrible, which I took in the forlorn hope that one day we’ll get photogrammetry software simple enough and clever enough to make some kind of model out of them.

So I think we need to simply accept that the name Dystylosaurus, while perfectly diagnosable based on its holotype and only specimen, is destined to remain a junior synonym for as long as Supersaurus is considered taxonomically valid.

But it does leave Dystylosaurus in a bit of a quantum superposition. When Supersaurus is considered diagnosable, it ceases to exist, like a cat in a box. When Supersaurus is considered undiagnosable, it pops back into existence, like … well, a cat in a box. It’s an unsatisfactory kind of existence, but I think that’s the way it has to be.

So Dystylosaurus has its day — and it ends up being disappointing. Despite being perfectly diagnosable, it’s dependent for its validity on our assessment of other taxa. Some fossils just can’t catch a break.