About that Saurophaganax paper

Newly out in VAMP:

Danison, Andy D., Wedel, Mathew J., Barta, Daniel E., Woodward, Holly N., Flora, Holley M., Lee, Andrew H., and Snively, Eric. 2024. Chimerism of specimens referred to Saurophaganax maximus reveals a new species of Allosaurus (Dinosauria, Theropoda). Vertebrate Anatomy Morphology Palaeontology 12:81-114.

Oh man, there is soooo much to say about this paper, which is a free download here. The short, short version is that OMNH 1123, the holotype specimen of the giant allosaurid Saurophaganax maximus, does not definitely belong to a theropod and may actually belong to a sauropod, and the same goes for some of the referred material, namely the atlas and chevrons. Since neither theropod nor sauropod material could be confidently assigned to Saurophaganax, we consider it a nomen dubium. That leaves a big ole pile of fossils from the Oklahoma panhandle that really do belong to a giant allosaurid, which we think is sufficiently distinct from Allosaurus fragilis and Allosaurus jimmadseni to warrant naming a new species, Allosaurus anax. If you want all the evidence and technical details and scientific reasoning, it’s in the paper, and some of it may make it into future blog posts. If you want to know what a weird ride this project has been, read on.

Who even are you?

The first point I want to make is that I myself have had just about every possible conflicting thought about the identity of OMNH 1123, the Saurophaganax holotype. I think chronologically I’ve gone through the following stages in this order: 

1. thinking it belongs to a theropod, for essentially all of my life before Andy Danison contacted me and invited me onto the project;
2. thinking it belongs to a sauropod, after Andy showed me how similar it is to the vertebrae of known juvenile sauropods;
3. thinking it belongs to a theropod, more or less in a panic after I published my last post about Saurophaganax and then worried that we were wrong and we were going to make fools of ourselves (or, more flatteringly, I made the strongest case I could for a theropod identity to stress-test our hypothesis, which an accurate description of the outcome but a lie about my motivation);
4. thinking it could plausibly belong to a sauropod, after Andy countered every point I raised in my “Saurophaganax is a theropod after all” push with photos of the same characters in the vertebrae of juvenile sauropods, which led to me agreeing with Andy and the other authors that designating Saurophaganax as a nomen dubium was the best move — this is the point of view that is crystallized forever in the new paper.

Also, I believe that at various points during the study the author team considered just about every possible scenario for dealing with the name Saurophaganax maximus, from thinking that it was a valid theropod genus and species, to thinking that it might be a valid sauropod genus and species (put a pin in that thought), to thinking that it was potentially valid but not definitively referrable to either Theropoda or Sauropoda, to realizing that if we couldn’t be certain if it was a theropod or sauropod, then no-one would be comfortable referring either theropod or sauropod material to it, which pushed us toward designating it a nomen dubium. We also considered a lot of potential taxonomic acts, including naming a new genus, naming a new species, or not naming the giant Oklahoma allosaurid and leaving it as Allosaurus sp. In the end, we decided a new species best captured our thinking about the material, and was most likely to be stable over the long run.

Am I sure about this?

Heck no! I’m the same guy who thought the Saurophaganax holotype was definitely a theropod, and definitely a sauropod. I remember the logic and evidence I used to reach each of those conclusions; I remember the certainty I felt in each one of those states; I remember the confidence that certainty gave me. But I think now that it was false confidence. I’m happy with the work we did in this paper, and I’m proud of it, and I think we came to the least-bad solution. But I’m sure this will not be the last word on Saurophaganax, and future authors may discover things we overlooked, or come back with a new perspective when and if new material of the giant Oklahoma allosaurid comes out of the ground.

Here’s what gives me pause: the accessory laminae in the Saurophaganax holotype are pretty much dead ringers for the spinoprezyg laminae (SPRLs) in the giant Oklahoma apatosaurine. I didn’t figure that out, Andy Danison did, and it’s one of those things that has just kept growing and growing in my mind, even after the paper was finalized. No other allosaurid or allosauroid or theropod of any description that I know of has prominent bars of bone in the same place, but they’d be expected in the neural arch of a juvenile diplodocid. And at this point I think it’s bordering on special pleading to argue that the giant Oklahoma allosaurid just happens to have these bars of bone, unique among theropods, that look identical to the SPRLs of a juvenile diplodocid, in a quarry dominated by diplodocids. So as of this evening/early morning, sitting here writing this post, I’ve about talked myself back around to thinking that the Saurophaganax holotype belongs to a sauropod, and possibly to a juvenile of the giant Oklahoma apatosaurine. 

The most obvious argument against is that whatever OMNH 1123 is, it had strongly-up-tilted transverse processes, like Haplocanthosaurus and a lot of theropods (see the Discussion in Boisvert et al. 2024) and very much unlike, say, OMNH 1366 and other dorsals of adult diplodocids. But I now think this is ontogenetically plastic — the juvenile Barosaurus specimens described by Melstrom et al. (2016) and Hanik et al. (2017) also have strongly up-tilted transverse processes. And in case I get hit by a bus before I can explain this more fully, it’s pretty clear that the neural arch telescopes in the dorsoventral direction over the course of ontogeny, and someone should work on that, too.

Anyway, the specter of Saurophaganax as a sauropod is a good segue to the next section.

What if we’re wrong?

I wrote up above about the comforting certainty of thinking that the Saurophaganax holotype definitely belonged to a theropod, or definitely belonged to a sauropod. I think that was in part because the intermediate idea, that OMNH 1123 could be either thing, feels inherently unstable to me. Surely someone will come along and point out some feature or combination of features that makes OMNH 1123 either definitely theropod or definitely sauropod. What then? Here are the possibilities I’ve thought of:

1. OMNH 1123 definitely belongs to a theropod, and it’s diagnostic enough to hang a species name on: then it goes back to being Saurophaganax maximus or Allosaurus maximus depending on how people calibrate their genericometers, Allosaurus anax becomes a junior synonym, and we were just flat wrong (see our discussion of this possibility on p. 107 of the new paper).
2. OMNH 1123 definitely belongs to a theropod, but it’s not diagnostic enough to hang a species name on: Saurophaganax remains a nomen dubium, just a nomen dubium with a home, and Allosaurus anax remains the valid name for the giant Oklahoma allosaurid.
3. OMNH 1123 definitely belongs to a sauropod, but it’s not diagnostic enough to hang a species name on: Saurophaganax remains a nomen dubium, just a nomen dubium with a home (in Sauropoda or Neosauropoda this time), Allosaurus anax remains the valid name for the giant Oklahoma allosaurid, and the giant Oklahoma apatosaurine remains unnamed.
4. OMNH 1123 definitely belongs to a sauropod, and it’s diagnostic enough to hang a species name on: well, Allosaurus anax remains the valid name for the giant Oklahoma allosaurid, and the implications for the giant Oklahoma apatosaurine are…real interesting.

I don’t think #1 is likely, but I don’t think it’s impossible. Option #2 seems the least likely to me: if OMNH 1123 belongs to a theropod, surely the unprecedented accessory laminae would make it highly diagnostic — this was the cornerstone of Dan Chure’s case in his 1995 paper naming Saurophaganax. Option #3 seems the most likely to me, for reasons explained above; instead of accessory laminae that are unique among theropods,* the weird bars of bone in OMNH 1123 would be bog-standard SPRLs, and the specimen could plausibly belong to any of several diplodocids known from Oklahoma Morrison.

* To be clear, the fact of some accessory laminae somewhere would not be unique to OMNH 1123 among theropods, but accessory laminae that mimic sauropod SPRLs would be.

Option #4 doesn’t seem very likely to me, but it is fascinating to consider the implications. I’ve long suspected that the giant Oklahoma apatosaurine represents a new species at least, based on a bunch of characters I’m not going into in this post, but I’ve never done the thesis-equivalent of work that it would take to persuasively demonstrate that. There is a scenario in which OMNH 1123 might be shown to belong to Apatosaurinae, in which case the combination Apatosaurus maximus could be on the table. Or Saurophaganax might become the third genus of apatosaurine alongside Apatosaurus and Brontosaurus, which seems insane, but there’s a plausible path to that result. OMNH 1123 wouldn’t be my first pick of holotype for the giant Oklahoma apatosaurine, and it could belong to a non-apatosaurine diplodociod, in which case no issues would arise for Apatosaurinae. Still, by lobbing the specimen vaguely (but not definitively!) sauropod-wards we may have created future headaches for sauropod workers in the Oklahoma Morrison. But we had to slay the dragon in front of us, not all the dragons everywhere forever.

Also, I should note that I’m a firm nominalist: to me names are hypotheses, and we should keep them around as long as they’re useful. I’m betting that Allosaurus anax is going to be a better fit for the giant Oklahoma allosaurid, but time will tell. And speaking of the name… 

The name

I love the name Allosaurus anax. I didn’t come up with it, Andy did. Here’s why I like it so much: 

1. Most importantly, although we came to different conclusions than Chure (1995) about the identity of OMNH 1123, we like and respect Dan Chure and his work, and we didn’t want the new paper to be seen as a criticism of his work. I always thought Dan showed a lot of generosity of spirit in creating the name Saurophaganax maximus, honoring J. Willis Stovall and salvaging Stovall’s intent with the original, defunct name Saurophagus maximus. Similarly, I thought it was just perfect that Andy wanted to honor Chure’s work and salvage his intent by creating the species name Allosaurus anax.
2. The species name anax means “king”, and there’s a nice parallel there to Tyrannosaurus rex. Allosaurus rex would sound derivative. I’m hardly unbiased here, but to me Allosaurus anax sounds wicked awesome.

Our reviewers

If I could have picked any two peer reviewers in the world for this paper, I would have picked Jerry Harris and Tom Holtz. Jerry because he’s described skeletons of an allosauroid (Acrocanthosaurus, in Harris (1998) and a diplodocoid (Suuwassea, in Harris & Dodson 2004 and numerous subsequent papers), so he has experience with all of the clades where OMNH 1123 might land, and because he consistently gives very careful, constructive reviews. Tom Holtz because he’s extremely sharp on theropod morphology but knows a thing or two about non-theropod dinosaurs, too, and also provides very thoughtful reviews. In the actual event, we got them both, and I couldn’t be happier.

My coauthors

Wow, what a great team this was to work with. I went to grad school with Andrew Lee, but we never managed to publish together before this. I’ve admired Eric Snively’s work for years but never published with him before either, ditto for Holly Woodward and Danny Barta. Funny true story: the authorship order of the paper is different from that of the SVP abstract because Holly thought that she hadn’t done enough to earn second author status, and she wanted someone else to take it. But Danny and I both felt that way about our own contributions. In the end I let them persuade me, but I still feel odd about it — so much of what I did on this paper was just get schooled by Andy Danison. At best I think I was the whetstone to his blade, but he did all the cutting.

And that brings me at last to Andy. Good heavens, he worked his butt off on this project, in museum collections and in the literature, finding stuff I’d never noticed and making connections that had escaped me, and then explaining his findings to us with piercing clarity. It was humbling but also exhilarating, because I got to learn new stuff about sauropod vertebrae. I hope to get some of that stuff into a future post, but for now it’s way late and I must sleep. Congratulations, team! It’s been satisfying to work with each of you.

Parting shot: it’s beginning to look a lot like S’naxmas

Jenny and I were talking tonight about some of the big Jurassic Park/Jurassic World dinosaurs we have around the house, and I discovered that the Jurassic World Super Colossal Allosaurus was a thing. What could be better for a dinosaur-obsessed guy who just helped rename the real world super colossal Allosaurus? Jenny got online and found it in stock at the local Target, and I ended up racing through the store in the last five minutes before they closed to score one for myself. 

I hope to do some more blogging about this project. We didn’t go into it in a lot of detail in the paper, but some of the stuff Andy found has wild implications for Morrison sauropods. And it would be kinda cool to do a post-mortem on why I was certain that OMNH 1123 was a sauropod, then a theropod, and now maybe sauropod again. And talk about the referred specimens. And about pneumaticity. Just maybe not until after Christmas. Then again, who knows. I’m publishing on stinkin’ theropods now, so anything is possible. Watch this space.

Previous posts on Saurophaganax:

• About that Saurophaganax abstract (October 20, 2024)
• Friday phalanges: Megaraptor vs. Saurophaganax (April 19, 2013)

References

• Boisvert, Colin, Curtice, Brian, Wedel, Mathew, & Wilhite, Ray. 2024. Description of a new specimen of Haplocanthosaurus from the Dry Mesa Dinosaur Quarry. The Anatomical Record, 1–19. http://doi.org/10.1002/ar.25520
• Danison, Andy D., Wedel, Mathew J., Barta, Daniel E., Woodward, Holly N., Flora, Holley M., Lee, Andrew H., and Snively, Eric. 2024. Chimerism of specimens referred to Saurophaganax maximus reveals a new species of Allosaurus (Dinosauria, Theropoda). Vertebrate Anatomy Morphology Palaeontology 12:81-114.
• Hanik, Gina M., Matthew C. Lamanna and John A. Whitlock. 2017. A juvenile specimen of Barosaurus Marsh, 1890 (Sauropoda: Diplodocidae) from the Upper Jurassic Morrison Formation of Dinosaur National Monument, Utah, USA. Annals of Carnegie Museum 84(3):253–263.
• Harris, J.D. 1998. A reanalysis of Acrocanthosaurus atokensis, its phylogenetic status, and paleobiogeographic implications, based on a new specimen from Texas. New Mexico Museum of Natural History and Science 13:1−75.
• Harris, J.D. and Dodson, P., 2004. A new diplodocoid sauropod dinosaur from the Upper Jurassic Morrison Formation of Montana, USA. Acta Palaeontologica Polonica, 49(2):197-210.
• Melstrom, Keegan M., Michael D. D’Emic, Daniel Chure and Jeffrey A. Wilson. 2016. A juvenile sauropod dinosaur from the Late Jurassic of Utah, USA, presents further evidence of an avian style air-sac system. Journal of Vertebrate Paleontology 36(4):e1111898. doi:10.1080/02724634.2016.1111898

Source: https://svpow.com/2024/12/22/about-that-saurophaganax-paper/