Supersaurus, Ultrasaurus and Dystylosaurus in 2019, part 6: what happens to Supersaurus now?
July 2, 2019
Since the previous installment of this epic, we’ve taken two brief digressions on how little importance we should attach the colours of bones in our photographs when trying to determine whether they’re from the same individual: cameras do lie, and in any case different bones of the same individual can age differently. Since then — newsflash! — a third reason has become apparent in the case of the two Supersaurus scaps: the object we discussed as Scap A turns out to be a cast. A really good one, sure, but still: its colour tells us little about the colour of the actual bone.
If you doubt that, consider the scapulocoracoid referred to Ultrasauros (which we’ll be meeting again in the next post). Here is the real bone, at the North American Museum of Ancient Life (NAMAL), with me for scale:
BYU 9462, the scapulocoracoid referred by Jensen to Ultrasauros. Mike Taylor for scale, doing a Jensen. The signage reads: Brachiosaurus scapula and coracoid. Originally believed to belong to the genus Ultrasaurus (now invalid), this shoulder blade is from the giant herbivorous dinosaur Brachiosaurus, a replica of which is mounted in this room. The dinosaur that owned this scapula was over 65 feet long and could tower 45 feet above the ground. When collected by Jim Jensen at Dry Mesa Quarry (Colorado) in 1989, the scapula was believed to represent the largest dinosaur ever found. Note how many separate pieces are within the specimen. A tremendous amount of work is required to complete a fossil of this size. Specimen on loan from Brigham Young University’s Earth Science Museum. Late Jurassic/Early Cretaceous (about 144 million years ago)
And here’s Matt with the cast of the same bone that resides in the BYU collections:
As you can see, the cast has been prepared in a darker and browner colour than the pale greenish grey of the real bone (though don’t forget that cameras lie about colours, so we shouldn’t over-interpret this difference).
Aaanyway …
We finished up last time with the observation that the holotype scapulocoracoid of Supersaurus, BYU 9025, is not obviously diagnostic; and that since the cervical BYU 9024 that has been referred to it actually belongs to Barosaurus, we can’t trust any of the other referrals of big Dry Mesa diplodocid bones to Supersaurus; and that the name must therefore be considered a nomen dubium, resting as it does on non-diagnostic material.
Can the name Supersaurus survive? I think it can, and I see four possible routes to that happening.
Method 0: Everyone ignores these blog posts
This is only a blog, after all. No-one is obliged to pay any attention to anything we say here.
That said, Matt and I do have previous in transforming series of blog posts in to actual papers. Having invested so much effort into writing these posts, I do hope that I’ll be able to do the same thing in this case, so at some stage the ideas from this series should become part of the formal scientific record. (I make no promises about how long that will take.)
So assuming that we can’t all just walk away and pretend that none of this ever happened, are there better ways to save the name Supersaurus?
Method 1. Someone finds autapomophies
Matt and I are of course primarily vertebra jockies. We are not above studying the occasional taxon based on appendicular material, but our expertise lies in the domain of the axial. It’s perfectly possible that someone who understands sauropod appendicular anatomy better than we do could isolate some autapomorphies in the holotype scap BYU 9025, and Supersaurus would then be firmly founded on a diagnostic type specimen.
Can we find hope for this outcome in the results of phylogenetic analyses?
In Whitlock’s (2011) diplodocoid analysis, Supersaurus emerges with but a single autapomophy: “Anterior caudal neural spine height less than 150% centrum height” (page 44). Based, as it is, on a referred element, that doesn’t help us much here. (Although it’s worth noting that Whitlock scored this character as 0 for Supersaurus and 1 for Barosaurus, which does very slightly suggest that the referred caudal is not Barosaurus and therefore might belong to the same individual as the Supersaurus holotype. Yes, this is weak sauce.)
Tschopp et al.’s (2015) unnumbered supplementary file Apomorphies recovered by TNT under implied weighting is difficult to interpret: for example, a heading on the first page says simply “R_iw” and its counterpart on page 8 is simply “P_iw“. But the Supersaurus-relevant entries are the same under both headings. In both cases, they read:
Supersaurus vivianae BYU
Char. 258: 1 –> 0
Char. 274: 1 –> 0
WDC DMJ-021
Char. 165: 1 –> 2
Char. 172: 0 –> 1
Char. 174: 0 –> 1
Char. 257: 1 –> 2Node 137 (Supersaurus vivianae)
Char. 183: 1 –> 2
I read this as meaning that the two OTUs have autapomorphies as listed, and the node uniting them has a single synapomorphy. But all of these characters related to the presacral vertebrae (C165-C183 in the cervicals, C257-C274 in the dorsals). So again, there is nothing here to help us diagnose Supersaurus on the basis of the holotype scapulocoracoid.
Of course, that doesn’t prove that there there aren’t any diagnostic characters. Someone with a good eye for sauropod scapulocoracoids might find details missed by these phylogenetic analyses, whose remits were much broader. But the news so far is not good.
Method 2. Nominate a neotype from the BYU material
If we accept that there are probably no more than two big diplodocoids in the Dry Mesa quarry, and that one of them is Barosaurus (based in the big cervical BYU 9024), and that the “Dystylosaurus” vertebra BYU 4503 is not Barosaurus, then it must follow that it belongs to Supersaurus. Unlike the type scapulocoracoid BYU 9025, that vertebra probably is diagnostic (it’s an anterior diplodocid dorsal, yet its spine is unsplit) so perhaps Supersaurus could survive by being diagnosed on that basis.
How would this work nomenclaturally? I think it would be difficult. If I have properly understood Article 75 of the ICZN, you can only go ahead and designate a neotype “when no name-bearing type specimen (i.e. holotype, lectotype, syntype or prior neotype) is believed to be extant”. But the holotype scapulocoracoid exists (so far as we know, though we’re not sure where it is).
All is not necessarily lost, though. Paragraph 75.5 (Replacement of unidentifiable name-bearing type by a neotype) says “When an author considers that the taxonomic identity of a nominal species-group taxon cannot be determined from its existing name-bearing type (i.e. its name is a nomen dubium), and stability or universality are threatened thereby, the author may request the Commission to set aside under its plenary power [Art. 81] the existing name-bearing type and designate a neotype.” But that means writing an ICZN petition, and I’m not sure anyone wants to do that. The process is technical, picky and prolonged, and its outcome is subject to the whim of the committee. It’s quite possible someone might go to all the trouble of writing a petition, then wait five years, only to have it rejected.
The irony here is that when Curtice and Stadtman (2001) referred the “Dystylosaurus” dorsal BYU 4503 to Supersaurus, they were at liberty to sink Supersaurus into Dystylosaurus rather than vice versa. Then the unique dorsal vertebra would have become the holotype, and the surviving genus would have been nicely diagnosable. Curtice and Stadtman (2001) did not discuss this possibility; nor did Curtice et al. (1996) discuss the possibility of folding Supersaurus into Ultrasauros when determining that the holotype vertebra of the latter belongs to the same taxon as the former.
Curtice and his collaborators were likely following the principle of “page priority”: preferring Supersaurus over the other two genera as it was the first one named in Jensen’s (1985) article that named all three. However, page priority does not exist at all in the present version of the Code (see Article 24, Precedence between simultaneously published names, spellings or acts), and even in earlier versions was only a non-binding recommendation. So it was really Curtice’s and his friends’ choice which genus to retain.
But that ship has now sailed. According to the principle of first reviser (Section 24.2.1), the pubished actions of Curtice and colleagues established a new status quo, and their choice of genus stands.
Method 3. Nominate Jimbo as a neotype
We might conceivably give up on the mixed-up Dry Mesa material as too uncertain to base anything on, and nominate WDC DM-021 (“Jimbo”) as the neotype specimen instead. It may have less material in total than has been referred to Supersaurus from the Dry Mesa quarry, but the association is somewhat more solid (Lovelace et al. 2008:528).
In some ways this might be the most satisfactory conclusion: it would give us a more solid basis on which to judge whether or not subsequent specimens can be said to belong to Supersaurus. But as with method 2, it could only be done via a petition to the ICZN, and I suspect the chances of such a petition succeeding would be low because clause 75.3.6 of the Code says that neotype designation should include “evidence that the neotype came as nearly as practicable from the original type locality [of] the original name-bearing type”.
So I don’t think this is likely to work, but I mention it for completeness. (Also, I am not 100% sure how solid the association of the Jimbo elements is, as the wording in Lovelace et al. (2008:528) does hedge a little.)
In conclusion …
I think the best hope for the survival of the name Supersaurus would be the recognition of unambiguously diagnostic characters in the holotype scapulocoracoid BYU 9025. In comments on the last post, John D’Angelo has started to think about what characters might work here. We’ll see how that thread pans out.
On the other hand, do we even particularly want the name Supersaurus to survive? It’s a pretty dumb name. Maybe we should just let it die peacefully.
Next time — in what really, really, really will be the last post in this series — we’ll consider what all this means for the other two names in Jensen’s trio, Dystylosaurus and Ultrasauros.
References
- Curtice, Brian D. and Kenneth L. Stadtman. 2001. The demise of Dystylosaurus edwini and a revision of Supersaurus vivianae. Western Association of Vertebrate Paleontologists and Mesa Southwest Museum and Southwest Paleontologists Symposium, Bulletin 8:33-40.
- Curtice, Brian D., Kenneth L. Stadtman and Linda J. Curtice. 1996. A reassessment of Ultrasauros macintoshi (Jensen, 1985). M. Morales (ed.), “The continental Jurassic”. Museum of Northern Arizona Bulletin 60:87–95.
- Jensen, James A. 1985. Three new sauropod dinosaurs from the Upper Jurassic of Colorado. Great Basin Naturalist 45(4):697–709.
- Lovelace, David M., Scott A. Hartman and William R. Wahl. 2008. Morphology of a specimen of Supersaurus (Dinosauria, Sauropoda) from the Morrison Formation of Wyoming, and a re-evaluation of diplodocid phylogeny. Arquivos do Museu Nacional, Rio de Janeiro 65(4):527–544.
- Tschopp, Emanuel, Octávio Mateus and Roger B. J. Benson. 2015. A specimen-level phylogenetic analysis and taxonomic revision of Diplodocidae (Dinosauria, Sauropoda). PeerJ 2:e857. doi:10.7717/peerj.857
- Whitlock, John A. 2011. A phylogenetic analysis of Diplodocoidea (Saurischia: Sauropoda). Zoological Journal of the Linnean Society 161(4):872-915. doi:10.1111/j.1096-3642.2010.00665.x
Sauropod Vertebra Picture of the Week 
July 2, 2019 at 11:49 pm
Uh oh, the ignorant one posts first… my father is a retired radiologist, and it may or may not have been one of his journals that pointed out that modern imaging technology may be giving us too much info: when abnormalities are found, are they normal variation that was previously undetectable, and provoking too many false positive followup treatment, or is it wise to rule out pathology? Since paleontologists have pretty much the same level of detailed access to whatever fossil has been gifted to us by time and geology and chemistry, and since large animals tend to fossilize poorly – if I’m not being obvious, how confident are we that even striking things like “split vs not-split” ridges, are really – I mean, they’re different, but…. let me try another tack: if bone spurs (and cervical “ribs”) are the result really of living soft tissue stresses and not of developmental osteology, then with a monster this size, won’t there be unusual features on such a scap or vert if (to pick an extreme) this thing lived in the mountains and another cousin lived its whole life on flat land? …Hopefully someone with actual knowledge posted while I was typing…
And I must live too far from a nice museum like that, I haven’t had that look of glee like you two do with these scaps… I’m still trying to picture an animal that big to have these bones as just a part of its shoulder.
July 3, 2019 at 12:47 am
This is a very exciting series of posts. As for the name Supersaurus, I think it has its charms. It’s easy to remember and just rolls right off your tongue.
Now Thanos is a stupid dinosaur name. They just slapped another name onto a dinosaur. It’s named after 1 cervical vertebra and not much else.
July 3, 2019 at 2:27 pm
A great series of posts fellas! I think y’all 100% nailed it calling the massive BYU 9024 cervical Barosaurus. Likewise, I enjoyed the presented options above. Personally I am a fan of “Door #3”, and currently I am doing age determinate histology on “Jimbo”, so it will be interesting to see if the association between age and morphologies help to elucidate this matter any. Again great work!
July 3, 2019 at 4:18 pm
Thanks, Cary! I actually didnt know anyone was currently working on the Jimbo material, so it’s good to learn that.
(Now I start thinking: maybe we as a community should maintain a sort of open ongoing register to let people know what we’re working on. It could be searchable, maybe even in subtle ways like knowing about phylogeny so that if I ask who is working on diplodocines it would show me a record of someone working on Kaatedocus. You know what? I should built it in my spare time. HAHAHAHAHA!)
July 3, 2019 at 8:10 pm
Thanks for the shout-out!
If you ask me, Supersaurus should live or die as a name on the merits of its holotype. It doesn’t really have the kind of long history of taxonomic importance and stability that would make a neotype really called for. If it turns out that Supersaurus is dubious but Dystylosaurus is not, then so be it.
However, as evidenced by my comments on the previous post, I do think that Supersaurus has a distinctive enough collection to potentially support its validity. Of course, from my metaphorical armchair, I am hardly well-qualified to give more than some provisional suggestions of what characters to look at, and it would probably take some substantial up-close comparative study of a variety of diplodocid scapulae (including both Dry Mesa diplodocid scapulae) to evaluate the similarities and differences and figure out which ones have merit.
July 4, 2019 at 12:10 am
I’m loving this series too. Supersaurus has been in my consciousness since I got a copy of Elting and Goodman’s “Dinosaur Mysteries” as a birthday present in primary school. I suppose another possibility is that the very large Dry Mesa diplodocid assemblage is one individual and it is closely related to Barosaurus lentus (hence the shared cervical characters) but is not actually B. lentus (differences in the division of the neural spines and broader scapulae among other things). Then Supersaurus might stand (or could be sunk into Barosaurus as B. vivianae, if you so felt). I don’t think we can tell at the moment though further study of Jimbo might hold the answer – for instance do its cervicals show the Barosaurus-like features picked out by Mike and Matt?
July 4, 2019 at 12:12 am
I’ve really enjoyed this series Mike, thanks.
If the holotype of Supersaurus vivianae is non-diagnostic, then Supersaurus vivianae should be declared a nomen dubium. Dystylosaurus edwini would be resurrected (based on the holotype vertebra). I assume this would include the Jimbo material.
When Wilson & Upchurch (2003) decided that Titanosaurus indicus was found to be based on non-diagnostic material, it was declared a nomen dubium. Titanosaurus had a very long and rich taxonomic history, but no attempt was made to ‘save’ the genus. Supersaurus would go the same way.
An ICZN petition isn’t worth pursuing to retain Supersaurus as a valid genus. The case for designating a neotype for Supersaurus is quite weak. (A neotype was declared for Coelophysis bauri based on non-topotypic material, but this was a special case.)
Last but not least… If it’s clear that Supersaurus and Dinheirosaurus are congeneric (following Tschopp et al., 2015), then the Supersaurus material could be referred to Dinheirosaurus as a separate species – probably as the new combination Dinheirosaurus edwini.
July 4, 2019 at 12:16 am
Note that an autapomorphy isn’t essential to diagnose a genus, if you can find a unique combination of characters.
July 4, 2019 at 5:58 am
Mike Taylor wrote- “and that the name must therefore be considered a nomen nudem, resting as it does on non-diagnostic material.”
This would make it a nomen dubium, not a nomen nudum. Nomina nuda are not properly erected, due to breaking one or more ICZN rules, whereas nomina dubia are undiagnostic.
Tim Williams wrote- “If it’s clear that Supersaurus and Dinheirosaurus are congeneric (following Tschopp et al., 2015), then the Supersaurus material could be referred to Dinheirosaurus as a separate species – probably as the new combination Dinheirosaurus edwini.”
That’s impossible as Dystylosaurus has priority over Dinheirosaurus. Instead, Dinheirosaurus would become Dystylosaurus lourinhanensis.
As for how to proceed, I’d go with Method 1. But to make Supersaurus a nomen dubium, you have to find it indistinguishable from at least two other taxa. So the first step is, which two sauropods with known scapulocoracoids can’t be distinguished from Supersaurus’ scapulocoracoid?
July 4, 2019 at 8:55 am
(Mickey, thanks for spotting the nudum/dubium foul-up: now fixed.)
July 4, 2019 at 11:35 am
John D’Anglo: perhaps you’re right that, if the holotype scap proves non-diagnostic, the name should just be allowed to die. It’s been an important name in the non-technical literature (as you can see from Adam Yates’s comment!) but not in the technical literature. For example, no-one’s ever named a clade Supersaurinae or similar. And as I noted in the post, it’s not as though it’s an inherently awesome name, like Xenoposeidon or Brontomerus. In fact, Supersaurus is up there with the very dumbest of the dinosaur names we have right now.
July 4, 2019 at 11:39 am
Adam, you make a good point that the BYU diplodocid material could represent a single individual whose cervicals are indistinguishable from those of Barosaurus but whos postcervical materal differs diagnostically from it. That hadn’t really occurred to me. And yet the cervical is so very barosauriffic. Based on what I’ve seen in photos, the Jimbo cervicals don’t really resemble those of Barosaurus at all closely, but I’ve yet to study them in detail (and of course I’ve never seen the material in real life).
I do think that reassigning the species vivianae into the genus Barosaurus as a new combination would be the worst of all worlds. We’d be left with a taxon that was still not really diagnosable, and which was vulnerable to further name changes in the future. (But then I think all dinosaurs names should be monospecific genera.)
July 4, 2019 at 11:45 am
TimW, are you sure that the nme Dystylosaurus would leap back to life if Supersaurus were decared a nomen dubium? If that’s true, then it would not be a bad outcome. Whether it would include the Jimbo material, I don’t know. It would depend on the basis that Lovelace et al. used to refer their specimen to Supersaurus in the first place, and that is not very clear in the paper. (Dave and Scott, if you’re reading this and you can remember the details, perhaps you could comment?)
Thanks for the reminder of the Titanosaurus case, which is indeed somewhat parallel to this one — except that much more was riding on the name Titanosaurus. So if that could be squashed without the world ending, no doubt the same is true of Supersaurus.
You’re also right to bring up Dinheirosaurus, which I’ve not thought about at all; though Mickey is of course right that if the two species were joined within a genus, then the older Dystylosaurus would be the winner. But as I’ve already noted, I am not a fan of moving species between genera. Names are labels, and should remain unchanged; genus-and-species names are tiny phylogenetic hypotheses and are always subject to change.
July 4, 2019 at 11:50 am
Mickey, you wrote: “to make Supersaurus a nomen dubium, you have to find it indistinguishable from at least two other taxa”. That is news to me. Where does this rule come from?
July 4, 2019 at 2:12 pm
Quick! someone photoshop some guitar strings and tuning pegs onto that scap Matt’s holding. He looks ready to shred.
July 4, 2019 at 2:28 pm
Mike: If a taxon is indistinguishable from only one other taxon, that’s just being called synonymous with that taxon, which is why you need it to be indistinguishable from two.
It’s for that reason that I think Tschopp et al. were wrong to call Diplodocus longus a nomen dubium—it can be confidently identified as a species of Diplodocus, and clearly is different from D. hallorum, so either it’s the same thing as D. carnegii or it isn’t.
As for Supersaurus, I made the case on the other post that it is distinguishable from all diplodocids with known scapulocoracoids. Out of all of them, it seems most similar to Apatosaurus yahnahpin and the undescribed apatosaurine specimen BYU 1252-18531, and can clearly be distinguished from Diplodocus, Barosaurus, and all other apatosaurines. It would be nice to be able to compare the similarities and differences via direct observation of the specimens, though. In particular, the apparent difference in the position of the acromion between the two Supersaurus scapulae gives me some concern, and some of the ratios Tschopp et al. reported seem inconsistent with available figures to me.
The worst-case scenario, if you ask me, would be for a Supersaurus neotype to be designated but for it to turn out that the Supersaurus holotype was diagnostic after all—and not be the same species as the neotype!
July 4, 2019 at 7:22 pm
John, I think that to proclaim A as a synonym of B, you have to do more than say “We can’t find diagnostic features to tell them apart”. You have to isolate synapomophies that tie them together. Otherwise you’d have to synonymise Xenoposeidon (known only from a dorsal vertebra) with Haestasaurus (known only from a forelimb and a patch of skin).
That said, I do think you’re right to be cautious about designating a neotype, and not only because of the tedious process it would entail. 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.
July 4, 2019 at 11:57 pm
Mike – Dystylosaurus would certainly be reinstated as a valid genus, if the holotype is diagnostic at genus level (which seems to be the case). This would also require that Dystylosaurus is not referrable to another earlier named genus (which doesn’t seem to be the case).
Other material could therefore potentially be referred to Dystylosaurus – including Jimbo. As you say, it would depend on the basis that Lovelace et al. used to refer their specimen to Supersaurus in the first place.
Mickey – Yep, you’re right. Dinheirosaurus would *not* have priority over Dystylosaurus. My bad.
July 5, 2019 at 1:24 am
“to make Supersaurus a nomen dubium, you have to find it indistinguishable from at least two other taxa”.
Is this true? Not really – although I get what Mickey is driving at.
The trouble is, as mentioned earlier in this series, individual elements can show a great deal of variation in shape and proportions (intraspecific or ontogenetic variation; taphonomy; etc). I’d say that a taxon can be a nomen dubium if you are not convinced that features originally described as “diagnostic” could lie within the potential range of variation observed within other taxa.
One example is _Serendipaceratops_. This (alleged) ceratopsian was named in 2003 based on a single isolated ulna. Thereafter, it was usually treated as a nomen dubium. In a 2014 paper, the original authors struck back and argued that _Serendipaceratops_ was indeed a valid genus, because the exact shape of the holotype ulna was unique among basal ceratopsians. However, this was thin gruel. The shape of the ulna can vary within a given taxon (as is the case for _Leptoceratops_, known from multiple specimens). How would we know that any another ulna belonged to _Serendipaceratops_ – unless it had the *exact* same shape as the holotype ulna?
Similarly, for _Supersaurus_… would we recognize any other scap as belonging to _Supersaurus_?
Mickey’s criterion of “you have to find it indistinguishable from at least two other taxa in order to declare it a nomen dubium” is very difficult to apply in practice. The exact shape of the _Supersaurus_ holotype scap may be unique – but that alone doesn’t make it diagnostic, given that scap shape can vary within a single sauropod taxon.
July 5, 2019 at 8:38 am
John’s correct about what happens if a taxon is only indistinguishable from one other taxon- it’s a synonym. I thought it was implied that the remains for each taxon were comparable to each other, so that instances where elements aren’t shared or e.g. distortion makes the original anatomy uncertain don’t count. In any case, as Tim stated above, shared apomorphies aren’t necessary, only a unique combination of characters.
Tim Williams wrote-
“Mickey’s criterion of “you have to find it indistinguishable from at least two other taxa in order to declare it a nomen dubium” is very difficult to apply in practice. The exact shape of the _Supersaurus_ holotype scap may be unique – but that alone doesn’t make it diagnostic, given that scap shape can vary within a single sauropod taxon.”
And here again I thought it was implied I meant “taxonomically indistinguishable.” Obviously, no two bones are identical so technically every bone was originally distinguishable from every other bone. But Tim’s correct that determining which differences are taxonomically useful takes work and some subjectivity. Ideally you’d want a known population to check for variability in various features. And you’d want an established alpha taxonomy, which we do not have for Morrison diplodocoids. I for one think Tschopp’s taxonomy is far too split, though at least he has an objective criterion. Regarding potential interspecific variability, sauropods seem to have had a lot of appendicular cartilage, which could lead to less constrained bone shapes.
But we have a starting point- John’s proposed unique character combination for Supersaurus’ holotype. Do those vary within other sauropod taxa?
July 5, 2019 at 12:22 pm
As Mickey has already pointed out, I only mean that two taxa which share a unique combination of characters and have no informative differences should be regarded as synonymous, so it doesn’t really make sense for a taxon to be dubious with respect to only one taxon.
July 5, 2019 at 4:42 pm
To some extent, they do, but I think Supersaurus does stand out:
1. Expansion of the posterior end of the scapular blade: According to Tschopp et al.’s supplementary tables, non-Supersaurus flagellicaudates (BYU 1252-18531 notwithstanding) range from 1.46 to 1.88 in this ratio, and Supersaurus ranges from 1.98 to 2.00. Given the apparent individual variation of around 10-15%, Supersaurus might not be distinguishable from Barosaurus (1.88) but probably is not Diplodocus (1.64-1.84). BYU 1252-18531 resembles Supersaurus in this character (2.06), and Tate-001 is reported to have a low ratio (1.70) by Tschopp et al. but is both drawn and described as having a high ratio by Filla and Redman 1994.
2. Symmetry of distal end of blade. Diplodocus hallorum and some apatosaurines appear to have an asymmetric distal end of the blade, with the posterodorsal corner located anterior to the posteroventral corner with the blade oriented horizontally. It is more symmetrical in all other diplodocids, including both Supersaurus specimens.
3. Length of scapula to minimum width of blade: Diplodocus hallorum, Supersaurus vivianae, and some apatosaurines are the only flagellicaudates with this ratio below 6.0, but this exhibits a fair amount of individual (and possibly ontogenetic) variation, and while Tschopp et al. report this ratio for both specimens, I wonder if they measured Scap B twice, as this ratio appears to be roughly 6.6 in Scap A from the photos here.
4. Ventral bump on blade: I am not certain of Tschopp et al.’s accuracy in scoring this character, as CM 3018 is scored as having it but appears to lack it, and CM 94 is scored as lacking it but appears to have it. Whether this is individually variable in any diplodocid depends on the status of BYU 1252-18531. In either case, it is ambiguous in Scap A of Supersaurus.
5. Orientation of acromial ridge relative to scapular blade: This appears to exhibit a range of around 10-12° in several species, including Supersaurus (77-88°), but Barosaurus and Tornieria are clearly distinct in this character (56-64°). This might be influenced slightly by perspective.
6. Position of acromion: This varies between Scap A and Scap B, with Scap A resembling Diplodocus, Barosaurus, and Tornieria in having an acromion near the midpoint of the scapula and Scap B resembling apatosaurines and Galeamopus in having an acromion near the glenoid level. Even in Scap A, though, the acromion appears to be more anterior than in D. carnegii or Barosaurus. This might be influenced slightly by perspective.
7. Fossa posterior to acromial ridge: Most diplodocids have a fossa posterior to the acromial ridge. A. ajax, A. louisae, A. immanis, and BYU 1252-18531 do not. Whether this is individually variable in any diplodocid depends on the status of BYU 1252-18531.
8. Size of coracoid: Supersaurus appears to have an anteroposteriorly shorter coracoid than most diplodocids, resembling Diplodocus carnegii and Brontosaurus yahnahpin most closely. This is probably influenced by perspective, but it seems unlikely that Supersaurus had as long of a coracoid as in most diplodocids, and the difference (particularly with most apatosaurines) appears to be outside of the range of individual variation.
All told, Supersaurus appears to be distinct from every known diplodocid with a described scapula:
Atlantosaurus immanis: #4, #7, #8
Apatosaurus ajax: #4, #7, #8
Apatosaurus louisae: #1, #2, #4, #7, #8
Brontosaurus excelsus: #1, #4, #8
Brontosaurus parvus: #1, #4
Brontosaurus yahnahpin: #4
Galeamopus pabsti: #4, #8
Tornieria africana: #1, #4, #5
Barosaurus lentus: #5, #8, possibly #6
Diplodocus hallorum: #1, #2, #8
Diplodocus carnegii: #1, possibly #6
#6 is the only taxonomically informative character the two scapulae appear to significantly differ in that I’ve been able to evaluate. As they appear to differ from each other in only one taxonomically informative character and they differ from almost all other diplodocids in at least two, I conclude that Supersaurus vivianae is probably a valid species based on the two scapulae but that it is possible that it belongs to Brontosaurus or Diplodocus, and is most likely to be synonymous with Brontosaurus yahnahpin or Diplodocus carnegii out of all comparable species.
July 6, 2019 at 6:56 am
Supersaurus will remain valid unless BYU 9025 sinks into an already existing genus. Maybe Jimbo will be transferred to a new species in the future.
July 6, 2019 at 9:34 am
Well, I think John’s comment satisfies Method 1. Supersaurus is diagnostic based on its holotype scapulocoracoid pending any dispute.
July 7, 2019 at 11:54 pm
John – using these same scapula-related characters, would you also regard Atantosaurus immanis as a valid species?
July 8, 2019 at 3:23 pm
I’m not sure if my comment went through the first time, but:
I’m sorry, but I don’t really see what the scapulocoracoid characters I’ve listed really have to do with the validity of Atlantosaurus immanis. The NSMT specimen Tschopp et al. regard as conspecific with the A. immanis holotype has an overall fairly typically apatosaurine scapulocoracoid.