Eighteen months ago, I noted that the Carnegie Museum’s Diplodocus mount has no atlantal ribs (i.e. ribs of the first cervical vertebra, the atlas). But that the Paris cast has long atlantal ribs — so long the extend past the posterior end of the axis.
There were two especially provocative comments to that post. First, Konstantin linked to a photo of the Russian cast (first mounted in St. Petersburg but currently residing in Moscow). I’ll reproduce it here:
Carnegie Diplodocus, Russian cast, head and anterior neck in left lateral view showing smallish, straight atlantal ribs. Our thanks to Konstantin for this photo.
As you can see, there are atlantal ribs on this specimen, but they do not resemble those of the Paris cast. These are much shorter, narrower, and lacking in structure. I have not to my knowledge seen anything like this on any other Diplodocus, and my guess — it’s only a guess — is that these were added by the Russians at some stage in this specimen’s very complex history.
But wait, there’s more!
In another comment on the same post, Crown House linked to a 3D model of the Vienna cast that has been posted to Sketchfab. It’s a pretty low resolution model, but if you zoom and pan, you can see that it has large and complex Paris-style atlantal ribs:
Carnegie Diplodocus, Vienna cast, head and anterior neck in left lateral view, showing large atlantal ribs.
Although these resemble the atlantal ribs of the Paris mount, they are not identical: the wavy margins face posteriorly rather than anteriorly as in both the Paris mount and Holland’s (1906) illustrations; and the proximal end has a dorsal expansion.
So we seem to have (at least) four different state of atlantal ribs in different casts of the same Diplodocus:
- Absent in Pittsburgh and London
- Small and rod-like in Moscow
- Long with a wavy dorsal margin in Paris
- Long with a wavy ventral margin and a proximal dorsal expansion in Vienna
Can anyone offer informed speculation on how this state of affairs came about?
But then things get weird. If you manoeuvre your way around the model to look up at this region from below:
Carnegie Diplodocus, Vienna cast, head and anterior neck in left ventrolateral view, showing lateral processes of the atlas.
Well, what the heck are we seeing here? There are two spiny processes, one on each side, projecting laterally from the ventral part of the atlas, and swept back at mid-length.
I have never seen anything like this in any sauropod — or, come to think of it, any other animal, but I admit I don’t pay much attention to other animals.
Does anyone have any idea what these projections are? Remember you can go to the model and look at them in 3D.
Pneumatic dorsal ribs in a selection of ornithodiran taxa. Clades that lack pneumatic ribs have been omitted, including non-dinosaurian dinosauromorphs, ornithischians, all early diverging sauropodomorphs, and numerous sauropods. The only included clade for which dorsal rib pneumaticity might be synapomorphic is Titanosauriformes. Phylogenetic relationships of the sauropods are based on Mannion et al. (2013) for titanosauriforms (note that the position of Brontomerus is uncertain), Tschopp et al. (2015) for diplodocoids, and Zhang et al. (2022) for Xinjiangtitan. Ribs are not shown to scale. Ribs traced from Butler et al. (2009:fig. 1b, Raeticodactylus), Campana (1875:fig. 8, Gallus), Madsen Jr. and Welles (2000:plate 19, Ceratosaurus), Zhang et al. (2022:fig. 14, reversed, Xinjiangtitan), a photo of WDC-DMJ-021-134 provided by David Lovelace (Supersaurus; see Lovelace et al., 2007), Gilmore (1936:plate 29, reversed, Apatosaurus), Riggs (1904:plate 75, Brachiosaurus), Janensch (1950:fig. 108, reversed, Giraffatitan), Wilson and Upchurch (2009:fig. 21, reversed, Euhelopus), Taylor et al. (2011:fig. 7, Brontomerus), and Curry-Rogers (2009:fig. 30, Rapetosaurus). King et al. (2024:fig. 3).
New paper out today with Logan King, Julia McHugh, and Brian Curtice, on pneumatic ribs in Apatosaurus and Brontosaurus (King et al. 2024).
This one had an unusual gestation. In the summer of 2002 2022 I did a road trip to Utah and western Colorado with my friend and frequent collaborator Jessie Atterholt. We did day trips to other collections, but we used Dinosaur Journey in Fruita as home base, and spent most of our time there. That’s where I first met Logan King, who was then recently graduated from Mike Benton’s lab at Bristol. Logan was spending the summer working for Julia McHugh at the Mygatt-Moore Quarry, and Logan and Julia were writing up MWC 9617, a sauropod rib from Mygatt-Moore with interesting pneumatic features.
Now, I had been interested in pneumatic ribs in sauropods for many years, and I’d amassed a war chest of published examples. But I had to admit to myself that the hypothetical pneumatic rib paper I’d been planning was simply never going to be my top priority, and therefore I was never going to actually start it, much less finish it. Logan and I hit it off right away, and I told him I’d be happy to shove my folder of pneumatic rib examples his way, and if he found it useful, I’d be grateful for an acknowledgment. In the actual event, he and Julia asked me to come on as a coauthor, and we were steadily making progress.
That fall I happened to be at Research Casting International at the same time as Brian Curtice — we were both there to see Haplocanthosaurus delfsi while it was down off exhibit from the Cleveland Museum. I’d hung out with Brian a lot back in grad school, but with one thing and another we hadn’t seen each other in many years, and those few days at RCI were a welcome opportunity to rekindle our friendship (and start down the path to coauthorship). Brian also got a look at YPM 1980, the holotype skeleton of Brontosaurus excelsus, while it was at RCI for a remount. Lo and behold, he found unmistakable pneumatic cavities in two of the dorsal ribs of YPM 1980.
A, left rib I, and B, right rib II of YPM 1980, the holotype of Brontosaurus excelsus, in posterior view. King et al. (2024: fig. 2).
That’s pretty awesome for a few reasons. We already knew that the dorsal ribs could be pneumatic in Apatosaurus louisae, because one of the ribs of CM 3018 has a nice round pneumatic cavity. But there was no solid evidence of costal pneumaticity in Brontosaurus. Marsh (1896) figured a rib with pneumatic cavities and claimed it for Brontosaurus, but without a specimen number the referral was uncertain. Turns out there is costal pneumaticity in Brontosaurus, and not just any bronto, but the ur-brontosaur itself, YPM 1980. And in 143 years, no-one had clocked it (there’s a lot of that going around). It seemed silly to write up a pneumatic rib of Apatosaurus from Mygatt-Moore and not mention the newly-discovered rib pneumaticity in YPM 1980, so we brought Brian in on the project. The manuscript went through a genuinely constructive review process at JVP, and we were revising the text and figs last fall.
While I had the apatosaur rib pneumaticity paper with Logan, Julia, and Brian going on one burner, Mike went to Chicago, decided that Brachiosaurus ribs were worth looking at after all (full story here), and went and wrote an entire paper on them in essentially no time. So after deciding in July of 2022 that I was never going to get around to my sauropod rib paper and I should hand it off to someone else (which was absolutely the right decision), a mere 14 months later I found myself working on two sauropod rib papers simultaneously. But they were on different taxa and had somewhat different focuses, so I made my junior author contributions to both and tried not to let Brachiosaurus step on Apatosaurus’s toes. (In particular, Mike and I didn’t talk much about pneumatic ribs outside of Brachiosauridae because there was already a broader survey in Logan’s manuscript.) Brach flew through review and into print just before year’s end (Taylor and Wedel 2023), and now the apatosaurines have lumbered over the finish line. I’m proud of both papers, and very happy to have them out in the world.
Proximal rib head that compromises MWC 9617 in posterior view. The inset image depicts a line drawing of the section of the rib that preserves pneumatic fossae within the rib canal sulcus. Abbreviations: cp, capitulum; I, proximal pneumatic fossa; II, middle pneumatic fossa; III, distal pneumatic fossa; t, tuberculum. Scale bar equals 5 cm. King et al. (2024:fig. 1).
MWC 9617 is an interesting specimen, with a series of same-sized fossae running down the postero-medial side, inside a long sulcus. That’s the side of the rib where the intercostal nerve, artery, and vein would have run — because that’s where they run in all tetrapods — but that neurovascular bundle doesn’t usually sit in a sulcus in sauropod ribs (the same neurovascular bundle does sit in a groove on the underside of human ribs). Those fossae are too smooth and too regular to be pathological. Pneumatic excavations that far down the rib shaft are unusual but not unprecedented — some of the ribs of Paluxysaurus and the Wyoming Supersaurus have pneumaticity about that far distally, and then there’s the weird lonely foramen in the one rib of Brachiosaurus that Riggs (1904) did illustrate. And sometimes pneumatic diverticula do create repeated excavations that look almost identical; one of my favorite examples is the series of pneumatic foramina on the right side of the centrum in a cervical vertebra of (perhaps fittingly) Paluxysaurus. So this certainly looks like a large pneumatic excavation, which we might call a fossa or a sulcus, containing smaller subfossae excavated at regular intervals. That’s pretty cool, because although that general mode of pneumatization turns up now and then in vertebrae, nobody’s documented it in a rib before.
C5? of Paluxysaurus in right lateral view, traced from a photo I took at the Fort Worth Museum of Science and History back in 1990s. I should do a separate post just on this vert sometime — the pneumatic excavations on the left side of the centrum are completely different.
We think that MWC 9617 is a rib of Apatosaurus louisae, for a couple of reasons. One, A. louisae is the most common sauropod at Mygatt-Moore by a wide margin, so any given rib from MMQ is more likely to belong to Apatosaurus than to anything else. The other sauropods known from MMQ so far are Camarasaurus and an indeterminate diplodocine (Foster et al. 2018) — and no pneumatic ribs have ever been described for either Camarasaurus or any of the Morrison diplodocines. (That in itself is pretty weird, given that Diplodocus and especially Barosaurus have pretty complex and extensive vertebral pneumaticity. How did a thicc boi like Apatosaurus beat them to the punch on pneumatizing ribs?) Anyway, it’s more parsimonious that the pneumatic rib from the apatosaur-dominated quarry belongs to Apatosaurus, for which pneumatic ribs are already known, than that it belongs to Camarasaurus or a diplodocine, for which it would be a world first. Bottom line, if we’re wrong, that’s even more exciting.
What’s next? At some point, more stuff from Mygatt-Moore! Jessie and I made Dinosaur Journey home base for our 2022 research trip because neither of us had ever gotten more than one day at a time in that collection. With a whole week to play there, and Julia and Logan to show us weird stuff, we made a LOT of progress, and found some stuff even I didn’t expect. Watch this space.
If you’re around sauropod material, look at ribs. Even the ones that were described in the 1800s may surprise you. Describing pneumaticity is everyone’s business — if you see something, say something!
References
- Foster, J., Hunt-Foster, R., Gorman, M., Trujillo, K., Suarez, C., McHugh, J., Peterson, J., Warnock, J. and Schoenstein, H., 2018. Paleontology, taphonomy, and sedimentology of the Mygatt-Moore Quarry, a large dinosaur bonebed in the Morrison formation, western Colorado—implications for Upper Jurassic dinosaur preservation modes. Geology of the Intermountain West 5:23-93.
- King, J.L., McHugh, J.B., Wedel, M.J., and Curtice, B. 2024. A previously unreported form of dorsal rib pneumaticity in Apatosaurus (Dinosauria: Sauropoda) and implications for pneumatic variation among diplodocid dorsal ribs. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2024.2316665
- Marsh, O.C. 1896. The Dinosaurs of North America. 16th annual report of the U. S. Geological Survey, 1894-95, pt. I. US Government Printing Office, Washington, D.C.
- Riggs, Elmer S. 1904. Structure and relationships of opisthocoelian dinosaurs. Part II, the Brachiosauridae. Field Columbian Museum, Geological Series 2(6):229-247, plus plates LXXI-LXXV.
- Taylor, Michael P., and Mathew J. Wedel. 2023. Novel pneumatic features in the ribs of the sauropod dinosaur Brachiosaurus altithorax. Acta Palaeontologica Polonica 68(4): 709–718. doi:10.4202/app.01105.2023
Sauropod Vertebra Picture of the Week 