Haplocanthosaurus tibiae and dorsal vertebrae. Curtice et al. (2023: fig. 1).
Brian Curtice and Colin Boisvert are presenting our talk on this project at 2:00 pm MDT this afternoon, at the 14th Symposium on Mesozoic Terrestrial Ecosystems and Biota (MTE14) in Salt Lake City, and the related paper is in the MTE14 volume in The Anatomical Record. Here’s the citation and a direct link to the paper:
This one is exciting to me for several reasons, both personal and scientific. I’ve been friends with Brian Curtice and Ray Wilhite since the late 90s, but I’ve never published with them before now. It’s nice to have Colin Boisvert on board as well — he’s working on his Master’s at BYU, just like Brian and Ray did back when, and he’s a keen observer of the sauropod scene.
Turning to the science, the number of known Haplo individuals in the entire Morrison is small, probably fewer than a dozen, so any new Haplo material is nice to get. Also, Dry Mesa is a big, famous, productive, diverse quarry, and having Haplo in that quarry is interesting and important.
But to me the most exciting thing about this is that Dry Mesa now has the highest diversity of sauropod genera of any locality in the world. At least six valid, impossible-to-confuse sauropod genera are known from Dry Mesa (listed alphabetically here; we provide specimen numbers of diagnostic elements for each genus in the paper):
- Apatosaurus
- Brachiosaurus
- Camarasaurus
- Diplodocus
- Haplocanthosaurus
- Supersaurus
BYU 12613, a posterior cervical of a diplodocid, in dorsal (top), left lateral (left), and posterior (right) views. The centrum length is 270 mm, compared to 642 mm for C14 of D. carnegii. Wedel and Taylor (2013), Figure 7.
Alert readers may also recall BYU 12613, a posterior cervical that Mike and I called Diplodocus in our 2013 neural spine bifurcation paper, but which may actually pertain to Kaatedocus. All the Diplodocus material from Dry Mesa is small, and I’m not at all confident that I could tell small Diplodocus vertebrae from Kaatedocus, so out of an abundance of caution we’re calling it all Diplodocus for the purposes of counting genera.
BYU 11617, which sure as heck looks like Barosaurus to me, with a loooong swoopy centrum, big posterolateral flanges, and prezygs that overhang the condyle.
There are also vertebrae in the quarry that I’ve always considered to belong to Barosaurus, like BYU 11617 from this post. If Brian Curtice is right about BYU 9024 (this monster) belonging to Supersaurus rather than Barosaurus, then I’m no longer certain that we can distinguish Supes and Baro based on cervical vertebrae. So maybe those Baro verts actually belong to Supersaurus. But if they don’t — or if BYU 9024 itself belong to Barosaurus, as Mike and I have argued (in our 2016 SVPCA talk, and this post and this post) — then Barosaurus is a seventh sauropod genus from Dry Mesa.
The high sauropod diversity at Dry Mesa is exciting for a couple of reasons. One, it emphasizes the ridiculous productivity of the Morrison paleoenvironment. Yes, there were droughts and fires and landslides and whatnot — at least periodically, even at Dry Mesa (Richmond and Morris 1998). But there was also an environment — or rather, a series of environments — fecund enough to support many coexisting genera of whale-sized herbivores. That’s part of the Morrison story, too.
And two, this is relevant to the “problem” of Morrison sauropod diversity — the idea that there are just too darned many sauropods in the Morrison, no environment could have supported so many, and therefore Morrison sauropod taxonomy has to be messed up, buncha dumb paleontologists oversplitting genera and species because they don’t know any better. (For more on this idea, see Darren’s brilliant series of posts at Tetrapod Zoology; the concluding post, with links to all the rest, is here.)
I put “problem” in scare quotes because I think it’s illusory. In addition to Dry Mesa with its six or seven sauropod genera, there are a handful of Morrison localities with five sauropod genera, more with four, and gobs with three. Not surprisingly, the diverse localities tend to be the big ones, which at least hints that more quarries would have more sauropods if they were bigger — maybe only the biggest quarries did a decent job of capturing the diversity of sauropods on the landscape.
Brian Engh’s assemblage of large-bodied Brushy Basin dinos for Jurassic Reimagined Part 1. Coincidentally, though, if you swap in Supersaurus for Barosaurus — or maybe just add Supersaurus alongside Barosaurus — you’ll have the known sauropod diversity of the Dry Mesa Dinosaur Quarry.
One you have five or six sauropod genera coexisting closely enough to get buried in the same hole, I think the “problem” of Morrison sauropod diversity goes away. The Morrison Formation outcrops from New Mexico to Canada, from the Oklahoma panhandle and the Black Hills of South Dakota to central Utah, and spans probably 7 or 8 million years. Even four or five distinct habitats or communities across all that space and time (which might be unrealistically conservative — it could easily be several communities at a time, turning over every 2 or 3 million years*), each with four to six sauropod species, gets the species count waaay up there.
*But wait — doesn’t our figure up top show that Haplocanthosaurus persisted from the lower part of the Salt Wash to the upper part of the Brushy Basin? Sure, but not as the same species right the way through. There were probably something like half a dozen species of haplocanthosaurs in the Morrison — H. priscus, H. delfsi, the as-yet-unnamed-but-definitely-distinct Bilbey Haplo (Bilbey et al. 2000), the as-yet-unnamed-but-definitely-distinct Snowmass Haplo (Foster and Wedel 2014, Wedel et al. 2021), plus I assume a couple more when and if we get better material of the more fragmentary specimens. That would be consistent with the multiple known species of Apatosaurus, Brontosaurus, Camarasaurus, Diplodocus, etc. So sequential communities of Morrison sauropods probably had a lot of the same genera — there’s nearly always a Cam of some kind, some apatosaurine lurking around, etc. — but with different species across time, space, and paleoenvironmental conditions.
I think a big part of the problem is that it’s (maybe too) easy to think of the Morrison Formation as a single thing — like most formations — and to think that we can hold all of it in our heads at once. But the Morrison is a monster, more comparable to a group than to other formations, and not really comparable to any other dinosaur-bearing formation in terms of extent, productivity, and likely diversity of environments and habitats. (For an overview of Morrison environments through time, see Jurassic Reimagined Part 1.)
So, yeah. Morrison sauropod diversity was high, and we just have to deal with that. Plus, hey, now we have more Haplo to play with. Happy days all around!
References
- Bilbey, S.A., Hall, J.E., and Hall, D.A. 2000. Preliminary results on a new haplocanthosaurid sauropod dinosaur from the lower Morrison Formation of northeastern Utah. Journal of Vertebrate Paleontology 20(supp. to no. 3): 30A.
- Foster, J.R., and Wedel, M.J. 2014. Haplocanthosaurus (Saurischia: Sauropoda) from the lower Morrison Formation (Upper Jurassic) near Snowmass, Colorado. Volumina Jurassica 12(2): 197–210. DOI: 10.5604/17313708 .1130144
- Richmond, D.R., and Morris, T.H. 1998. Stratigraphy and cataclysmic deposition of the Dry Mesa Dinosaur Quarry, Mesa County, Colorado. Modern Geology 22:121-143.
- Wedel, Mathew J., and Michael P. Taylor. 2013. Neural spine bifurcation in sauropod dinosaurs of the Morrison Formation: ontogenetic and phylogenetic implications. Palarch’s Journal of Vertebrate Palaeontology 10(1):1-34. ISSN 1567-2158.
- Wedel, Mathew; Atterholt, Jessie; Dooley, Jr., Alton C.; Farooq, Saad; Macalino, Jeff; Nalley, Thierra K.; Wisser, Gary; and Yasmer, John. 2021. Expanded neural canals in the caudal vertebrae of a specimen of Haplocanthosaurus. Academia Letters, Article 911, 10pp. DOI: 10.20935/AL911
Sauropod vertebrae in anterior view exhibiting a spectrum of variation in the dorsoventral positions of the neurocentral joint. Wedel and Atterholt (2023: fig. 1).
As described in the last post, Jessie Atterholt is presenting our poster on this project today, at the 14th Symposium on Mesozoic Terrestrial Ecosystems and Biota (MTE14) in Salt Lake City, and the related paper is in the MTE14 volume in The Anatomical Record. Here’s the citation and a direct link to the paper:
I’ve been interested in neurocentral fusion in sauropods and other critters for a long time, especially when the neurocentral joint is shifted dorsally or ventrally relative to the neural canal. I noted some instances of those shifted joints in blog posts (one, two, three), but I didn’t know what to do with that information. The impetus to turn those observations into a paper came from two sources. First, working with Jessie got me thinking about shifted neurocentral joints as one more Batman villain in the rogue’s gallery of neural-canal-related weirdness in birds, sauropods, and other archosaurs. Jessie and I kindled the ambition to catalog that entire zoo — results of that mega-project so far are on a new sidebar page.
Fronimos and Wilson (2017: figure 2)
Second, I read Fronimos and Wilson (2017). This is an extremely cool paper and it’s a shame I haven’t blogged about it before. The authors went through the cervical and dorsal vertebrae of the holotype skeleton of Spinophorosaurus (GCP-CV-4229) and measured the complexity of the neurocentral joints. They found that joint complexity increased toward the base of the neck, maxed out in the anterior dorsals, and decreased in posterior dorsals. That’s consistent with the idea that complex neurocentral joints were an adaptation to increasing biomechanical stress on the vertebrae, which should likewise increase toward the base of the long, cantilevered neck and decrease toward the big anchor of the sacrum. The basic idea is that the complex joints increased the joint surface area and decreased the likelihood of traumatic dislocations — disrupting the joint between the arch and centrum would tend to cause life-ending spinal cord injuries.
Available surface area for the neurocentral joint in its normal position (below) and shifted dorsally, above the neural canal (above). The lower part of the neural arch is H-shaped in cross-section, with anterior and posterior fossae below the zygapophyses. The real-life example this is based on is in the last image in this post.
Reading that paper was a lightbulb moment for me. If the neurocentral joints of sauropods were adapted to resist biomechanical stresses, anything that increased the “contact patch” between neural arch and centrum would be desirable. From the standpoint of a neural arch and centrum trying to stick together, the neural canal is a flaw, a big dumb area of forced non-union. But you can’t get rid of the neural canal, which houses the spinal cord and the developmentally important spinal arteries (see Taylor and Wedel 2021 for more on the latter). The only way to eliminate the gap caused by the neural canal is to get around it by shifting the neurocentral joint dorsally or ventrally. John Gilmore famously said that the internet interprets censorship as damage and routes around it. We hypothesize that in an evolutionary sense, sauropod neurocentral joints interpreted the neural canal as damage and routed around it.
Of course you don’t have to be a sauropod to benefit from the enlarged contact patch between neural arch and centrum, as shown by the ’boutons’ of many mammals, including humans (unfused sheep vertebra shown above). But as Fronimos and Wilson (2017) pointed out, strengthening the neurocentral joints was probably especially important for sauropods, which grew rapidly for a long time and achieved large body size with many joints still unfused (see also Wedel and Taylor 2013: table 1, Hone et al. 2016: table 2). That would also explain why some sauropods went well beyond bouton territory, into having the neurocentral joint entirely dorsal or ventral to the canal.
Hey, it only took me five and a half years to get this idea out of my notebook and into a peer-reviewed paper!
There’s still the question of why the neurocentral joints shifted dorsally in some vertebrae and ventrally in others. The ventral shift in caudal vertebrae makes intuitive sense — the neural arch narrows dorsally, so shifting the joint upward would decrease the surface area, not increase it. Also, shifting the joint ventrally allowed the neural arch to be morticed between the transverse processes, which further increased the contact patch and made the neurocentral joint even stronger.
MB.R.3823, a dorsal centrum of Giraffatitan in posterodorsal view. The neurocentral joint surfaces of the centrum come together dorsal to the neural canal, leaving only a paper-thin gap.
What about dorsal vertebrae? In dorsal vertebrae of Haplocanthosaurus, Camarasaurus, and Giraffatitan, the neurocentral joint is shifted dorsally, to the point that in some Camarasaurus dorsals the joint lies completely above the neural canal. It’s not obvious why that would be more advantageous than shifting ventrally — except possibly that shifting ventrally might have interfered with pneumatization. In some unfused Cam dorsals, like the one shown below, the lateral pneumatic cavities are so big that they excavate right up under the dorsally-shifted neurocentral joint.
MWC 3630, an unfused dorsal centrum of Camarasaurus in right lateral (top) and posterior (bottom) views.
Still, pneumatic diverticula are thought to opportunistically occupy spaces that aren’t being loaded very much (Witmer 1997), so presumably they could make cavities above, below, or in any other direction from the neurocentral joint. We’re not really sure why the joint shifted dorsally in dorsal vertebrae of some sauropods. We know that the developmental program could accommodate shifts in both directions over fairly short distances in the same individual, because in the CM 879 skeleton of Haplocanthosaurus, the neurocentral joints are almost entirely above the neural canals in the dorsal vertebrae, and completely below the canals in the caudals. (The sacrals in that specimen are doing their own weird thing, about which more another time.)
DINO 4970, an unfused neural arch of Camarasaurus in the Carnegie Quarry (“the Wall”) at Dinosaur National Monument. The arch is in ventral view, with anterior toward the top. Note the butterfly-shaped neurocentral joint, with no gap for the neural canal.
Our paper is short and to the point because we don’t have a lot of data on this yet. Our sampling so far is basically limited to stuff we’ve stumbled over that made us go ‘huh!’ As with our work on paramedullary diverticula in birds, we hope that our work inspires more people to look into this weird stuff and document it — we can’t be sure about the rules until we know what all is out there.
References
- Fronimos, J.A. and Wilson, J.A., 2017. Neurocentral suture complexity and stress distribution in the vertebral column of a sauropod dinosaur. Ameghiniana, 54(1), pp.36-49.
- Hone, D.W.E., Farke, A.A., and Wedel, M.J. 2016. Ontogeny and the fossil record: what, if anything, is an adult dinosaur? Biology Letters 2016 12 20150947; DOI: 10.1098/rsbl.2015.0947.
- Taylor, Michael P., and Mathew J. Wedel. 2021. Why is vertebral pneumaticity in sauropod dinosaurs so variable? Qeios 1G6J3Q. doi:10.32388/1G6J3Q
- Wedel, Mathew J., and Michael P. Taylor. 2013. Neural spine bifurcation in sauropod dinosaurs of the Morrison Formation: ontogenetic and phylogenetic implications. Palarch’s Journal of Vertebrate Palaeontology 10(1):1-34. ISSN 1567-2158.
- Witmer, L.M. 1997. The evolution of the antorbital cavity of archosaurs: a study in soft-tissue reconstruction in the fossil record with an analysis of the function of pneumaticity. Journal of Vertebrate Paleontology 17(Supplement 1): 1-76.
BIG day today. The 14th Symposium on Mesozoic Terrestrial Ecosystems and Biota (MTE14) is taking place in Salt Lake City this week. Normally I’d be there in a heartbeat, but my son is graduating from high school next week and I’m far too busy to get away. Still, I’m an author on one poster and two talks that are running today, along with the three associated short papers that are published in the conference volume in The Anatomical Record.
I will be blogging about these things, and shortly, but for now here are Wedel-related presentations and links to the papers, in chronological order. (The whole conference volume is available here, I just extracted the papers I’m on as separate PDFs to post in the links below.)
1. Wedel and Atterholt on expanded neurocentral joints in sauropods — Jessie is presenting our poster, which should be up for most of the day. Citation and link to paper:
2. Curtice et al. on the first material of Haplocanthosaurus from Dry Mesa — I believe Brian Curtice and Colin Boisvert are tag-teaming this talk at 2:00 pm MDT.
3. Weil et al. on Morrison microvertebrates from the Oklahoma panhandle — Anne Weil is giving this talk at 2:15 pm MDT.
Stand by for more info on all this stuff. And if you’re attending MTE14, go catch these presentations and say hi to all these excellent human beings!
Sauropod Vertebra Picture of the Week 