Compact Thescelosaurus Year Ten

Twelve months have rolled along since our previous check on The Compact Thescelosaurus, now clocking in at a decade of existence. With Triassic and Jurassic pseudosuchians for the previous two years, the obvious addition was Cretaceous pseudosuchians, of which there were more than the previous two additions combined. The Cretaceous section wasn't quite so dominated by one group like the Jurassic was by thalattosuchians, but it was a great time to be a notosuchian.

Like this one, Simosuchus clarki. I took this photo when the traveling exhibit visited the Science Museum 11 years ago; Wikipedia is running a photo of the same mount from another stop on the itinerary.

Compact Thescelosaurus Year Nine

October and National Fossil Day have rolled around again (check out the fall 2024 Park Paleontology News, too!), so it's time to take a look at the previous year's changes to The Compact Thescelosaurus and welcome some new content. First, the new stuff: I'm sure you'll be shocked to find out I've followed up Triassic pseudosuchians with... Jurassic pseudosuchians. I'm rearranging the pseudosuchian content a bit, to have the non-crocodylomorphs on one sheet and the crocodylomorphs on another. This was done to forestall the deployment of an unwieldy number of "subdivision" columns. Provided I get far enough along, something similar might have to happen with the new sheet around Crocodylia or so. Anyway, the main takeaways I got out of Jurassic pseudosuchians are 1) there's been a lot of work on thalattosuchians over the past couple of decades, and 2) I've discovered I'm not very fond of thalattosuchians and certainly don't mind that they conk out midway through the Cretaceous.

Hey, it's the Science Museum "Goniopholis" again! (Most Jurassic pseudosuchians are thalattosuchians, but North America is largely bereft of the darlings, so we make do with crocs like these.)

Compact Thescelosaurus Year Eight

It's that time again, for National Fossil Day (October 11 this year), a new sheet for The Compact Thescelosaurus, and the annual summary of what was added to the spreadsheet in the past 12 months. In addition to National Fossil Day events this month, the latest issue of Park Paleontology News is up for viewing. Also in breaking NPS paleontology news: additional dating of the fossil human tracks at White Sands National Park, and a previously overlooked record of a tyrannosaur tooth at Yellowstone National Park. [Update, 2023/10/10: And a tritylodont bonebed at Glen Canyon National Recreation Area was just announced; goes well with this new paper on a massive track block from the recreation area, too.]

Here at Equatorial Minnesota, we've passed 400 entries this year. Later this year, December 15 will mark 10 years of posting. (Also, anyone know why this nautiloid post would have spiked in interest?) The Compact Thescelosaurus has been around for 8 of those years, and it's traditional to add a new sheet. For this year, first I considered all of Pseudosuchia (except for the aetosaurs, covered already), but decided against it due to the number of species. I then looked at doing just Mesozoic pseudosuchians before being discouraged by whatever it is Thalattosuchia has been doing over the past 200 years. So, for now it's just Triassic forms, with the intent to expand over time.

Prestosuchus threatening an Eoraptor in the "Ultimate Dinosaurs" exhibition at the Science Museum of Minnesota, May 2014.

Compact Thescelosaurus Year Seven

Here we are at the second weekend of October, which means it's time for three things: National Fossil Day; a new sheet for The Compact Thescelosaurus; and our annual roundup of what's been added to the spreadsheet. National Fossil Day falls on Wednesday, October 12 this year, although events occur throughout the month (especially the weekends before and after), so check your nearest museum or National Park System unit for events! Our fall Park Paleontology newsletter is also up for viewing (including more fun with packrats).

Detour into Choristodera

This week a paper on unusual prehistoric aquatic reptiles was published. I am speaking, of course, of Brownstein (2022) on choristoderes. (If you thought it was going to be spinosaurs, you must be new around here!)

We have a soft spot for choristoderes here at Equatorial Minnesota Towers, even if they rarely rate so much as an "and also featuring Champsosaurus" credit in sci-pop culture. Brownstein (2022) includes the classic Champ but is more focused on the short(er)-faced choristodere Simoedosaurus, although under a fresh coat of taxonomic paint: the North American species S. dakotensis is moved to the new genus Kosmodraco on the grounds of anatomical differences and differences in time and place from the type species, European S. lemoinei. It also gets a new friend, K. magnicornis. Which said, sure... but the species of Kosmodraco still clade more closely to Simoedosaurus than to anything else, so if your genericometer was so tuned, you could still include them in Simoedosaurus with a clear phylogenetic conscience. (There are a lot of anatomical differences between the two genera. My only quibble with Kosmodraco is that it's an awfully pretty name for a choristodere; it sounds more like an an extravagantly crested pterosaur. Meanwhile, Champsosaurus itself is still secretly a taxonomic booby trap waiting to be sprung. Sooner or later someone is going to do something with the various species that is entirely legal by the rules of taxonomy and yet manages to displease everyone else.)

The type skull of Kosmodraco magnicornis. It'll take a moment to orient yourself: the bitey part is surprisingly short (see the "r. lacrimal"? The eye was behind that). What you're looking at is a modest snout attached to a greatly flaring right "cheek" (which comes with a scalloped fringe). Figure 1 in Brownstein (2022). CC BY 4.0.

Either way, the skull is worth a look. There's garden-variety "weird" and then there's "why is this all practically all post-orbital?" (It certainly wasn't for intellect, most of the posterior of choristodere skulls being a series of struts and bars. Note that the maxillary teeth of Kosmodraco only go back as far as the eyes.) Champsosaurus, as we've already seen, had a long, narrow toothy muzzle, with the rest of the skull being broad and low. Kosmodraco had a skull that was still low but much more wedge-shape in dorsal view, as if someone smooshed or amputated a Champsosaurus-like snout. The business end of a Kosmodraco skull is an interesting analog for the modern alligator gar. It's the back of the skull where things get different, as Brownstein (2022) notes. Kosmodraco has a lot more skull going on behind the eyes, which themselves are elevated on skull like those of an alligator. The posterior margin is also ornamented with a series of knobs, and the skull is quite low (Brownstein 2022).

A comparison of the palatal regions of choristoderes Kosmodraco and Champsosaurus to an alligator and an alligator gar also serves as a comparison of basic facial shapes for the four. Similarities between Kosmodraco and the gar aren't as great if you continue through the rest of the skull. Figure 13 in Brownstein (2022). CC BY 4.0.

I'd like to take the opportunity to note that there's another extinct group of aquatic tetrapods with flat, blunt, broad skulls and eyes relatively far forward on the skull, which has so far avoided comparisons to Simoedosaurus/Kosmodraco: the metoposaurid amphibians of the Triassic. Again, it's not a perfect comparison (metoposaur snouts are blunter), but it would seem to point to the long-term existence of a niche for freshwater predators with certain cranial adaptations.

One of the other points noted by Brownstein is there is more diversity in choristoderes than you might suspect by simply looking at the number of genera. For example, as of this writing Champsosaurus is composed of several species over about 20 million years. North American specimens have tended to be lumped with either the short-faced Simoedosaurus or the long-faced Champsosaurus.

References

Brownstein, C. D. 2022. High morphological disparity in a bizarre Paleocene fauna of predatory freshwater reptiles. BMC Ecology and Evolution 22: article number 34. doi:10.1186/s12862-022-01985-z.

Compact Thescelosaurus Year Six

The time has come again for the annual review of The Compact Thescelosaurus. This year's new page is on aetosaurs and their close relatives, with the classification diagram page updated. (Don't forget, Wednesday the 13th is also National Fossil Day!)

Aetosaur Desmatosuchus spurensis is one of the subjects of the NPS Prehistoric Life Coloring Book. Coincidentally, an aetosaur also featured in the 2014 National Fossil Day artwork.

Compact Thescelosaurus Year Five

It's time for the annual review of The Compact Thescelosaurus. As is traditional, there's a new sheet, which this year covers mosasaurs, as you might have guessed from the image. The classification diagram page has been updated as well. (Don't forget, Wednesday the 14th is also National Fossil Day!)

Mosasaurus conodon, hanging out at the Science Museum.

Compact Thescelosaurus Year Four

It's time for the annual update to The Compact Thescelosaurus, now entering its fifth year. This time, ichthyosaurs join the group, which is really stretching it for me, but hopefully it's not entirely in vain. Ichthyosaurs fared a bit better than plesiosaurs in that *only* 91 of the 224 species (40.6%) included are of questionable validity, rather than 173 of 318 (54.4%). (Only.) My go-to work was McGowan and Motani 2003 on Ichthyopterygia (Handbook of Paleoherpetology 8), just to figure out what was there. Ichthyosaurus itself, like Plesiosaurus, accumulated an awe-inspiring retinue of species over the years, but it's not alone. A couple of areas of ichthyosaur taxonomy are pretty volatile at the moment as massively specious genera are re-evaluated, so expect revision. (Also expect the usual formatting bugs and obvious corrections that come with a new sheet.)

Sure, like you don't know what an ichthyosaur looks like. This was found at Wikimedia Commons, but originally came from a short item by William Diller Matthew in the American Museum Journal for January 1908.

New Pages: Geologic Time Scale and Classification Diagrams

So far the year has been quiet (well, up until Friday), so I thought I'd address a couple of nagging things, which I've done by adding two pages. The first page is a geologic time scale figure, from one I worked up for National Park Service reports. It's the kind of thing I thought would be handy to have on hand here for reference, instead of having a link to an external site. It'll be updated from time to time as dates are refined. The Quaternary is rather cramped, although I don't feel particularly apologetic for shortchanging Homo sapiens.

The second page is a sort of "map" to the classifications used in the various sheets over at The Compact Thescelosaurus, made with classic ASCII cladograms. (I contemplated drafting them in other ways, but none of them were as amenable to updating.) I thought this would be useful for visualizing the mess of classification columns. The process also forced me to look at the positions of a few clades, as you may have noticed from the updates sheet.

It's not connected to either topic, but I've also added a paragraph of new information to the post on the "Kweichow sauropod" after coming across a mention of it in Averianov and Sues (2017).

Finally, so as not to leave the post without an image, here's one attached to a quick story:

Back in spring 2001 I was on a field trip to the Badlands/Black Hills area of southwestern South Dakota. We were stopped along a road near Deadwood for lunch. One of the professors said something to the effect that "there are fossils in this formation." I looked down at the chunks of rock at my feet and said "You mean like this?"

Yeah, like this.

From my notes the source is the Whitewood Formation (or Dolomite, or Limestone), fittingly enough an (surprise, surprise) Upper Ordovician unit. More on its cephalopods can be found in Miller and Furnish (1937).

References

Averianov, A., and H.-D. Sues. 2017. Review of Cretaceous sauropod dinosaurs from central Asia. Cretaceous Research 69:184–197. doi:10.1016/j.cretres.2016.09.006.

Miller, A. K., and W. M. Furnish. 1937. Ordovician cephalopods from the Black Hills, South Dakota. Journal of Paleontology 11(7):535–551.

Year One of The Compact Thescelosaurus (now with extra choristoderes)

Mid-October is the time of National Fossil Day, as well as just past the anniversary date of the late lamented Thescelosaurus! and the introduction of The Compact Thescelosaurus. In honor of the occasion, I've made a couple of additions. One is a new page with a selection of online museum collections databases. The other is a new worksheet on The Compact Thescelosaurus, featuring choristoderes. This sheet is the first of what I hope to be a series covering other fossil groups; choristoderes were selected for the honor this time around because there are only a few. I have a few candidates in mind for the next addition, perhaps a year from now; it depends on how ambitious I'm feeling. I haven't given up on the idea of making a version of the old website's contents available, but I haven't really decided how to do it.

So it's not really surprising that I came up with a post on subtle nuances of the nomenclature of Champsosaurus.

Champsosaurus: Adventures in 19th century taxonomy

It all started innocently enough with a couple of paragraphs in the 1870 Proceedings of the Academy of Natural Sciences, submitted on behalf of Joseph Leidy. The item notes that Leidy had received a reptilian vertebral centrum (the body of the vertebra, minus all the processes and such) collected by Ferdinand Vandeveer Hayden from the Moreau River, probably from Cretaceous rocks. It reminded Leidy of the vertebrae of marine reptiles, specifically Nothosaurus, so he proposed to name it Nothosaurops, type species N. occiduus. So far, so good. He got around to a longer description in 1873, in which he mostly repeated the 1870 information, but also included some figures of the fossil. Unfortunately, somebody goofed, because the text refers to something called Nothosaurus occiduus, but the plates and captions are using Nothosaurops occiduus. This would not be of much modern interest except for the fact that there is a good chance the specimen is the first described fossil of Champsosaurus.

Won't somebody please think of the champsosaurs?

Every so often, you may stumble across a crocodile-like thing lurking at the edge of your typical "two-page spread of all kinds of prehistoric critters" found in popular dinosaur books. If the book is of any quality, it includes a legend identifying the denizens, and the crocodile-like thing will be tagged "Champsosaurus" (if there isn't an error in the legend, of course). Unless you're intrigued by the name, or something else tickles your fancy, you'll probably continue along. There are a lot of crocodiles and crocodile-like things to keep track of, after all. What makes this one unusual?