New paper: Curtice et al. (2023) on the first Haplocanthosaurus from Dry Mesa

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