Speleotherium logani

It would be easy to think that we've got the large Late Pleistocene mammals of North America pretty well locked down. After all, every self-respecting animal of that stripe has a long list of synonyms and pseudonyms, sometimes going well back into the 19th century. (All right, to be fair, horses are a mess if you look closely.) Even here, though, there can be surprises. Recently we had the Pacific mastodon and the re-establishment of the dire wolf in its own genus, and now we have the recognition of an entirely new genus and species of scrubox, Speleotherium logani (White et al. 2025).

If you know a bit of Greek, you'll get the idea that the name indicates we're dealing with a beast ("therium") associated in some way with caves ("speleo"). The holotype and best specimen of Speleotherium logani did indeed come from a cave, and in fact was partially encrusted with cave deposits (which certainly give it an unusual look but haven't made it easy to prepare or interpret). A few years ago the skull was photographed for a photogrammetric model, and you can take it for a spin and see the deposits, particularly on the right side of the face. This specimen and others were discovered in 1976 in what is now called Muskox Cave in its honor, within Carlsbad Caverns National Park, New Mexico. The species name honors the discover, Lloyd Logan. Although the name literally translates to "Logan's cave beast", the authors suggest the common name "Logan's austral scrubox" instead (White et al. 2025).

Figure 31 from Kottkamp et al. (2020), used in several other places as well (including White et al. 2025). You're looking at the back of the skull, going off to the right. Other bones are also visible, as well as the coating of cave mineralization.

The Muskox Cave fossils were long thought to belong to the shrubox Euceratherium (which is the name used for it at the 3D model above). That's how we labeled them in recent inventories of the park's fossils, for example (Kottkamp et al. 2020, 2022). It was not until White et al. began to prepare the specimens that it became apparent that there was something else here. Euceratherium has a narrow "forehead" and complexly twisted horn cores, whereas the Muskox Cave skull has a broad "forehead" and less curvy cores. The metapodials (metacarpals and metatarsals) are also shorter and stockier, which twigged something else; the authors knew of similarly proportioned metapodials of an animal similar to but much smaller than Euceratherium from sites in Mexico and Belize, but had never had a face to go with them. Speleotherium is therefore not a "one-off" but something that had a fairly wide range in North and Central America, and there are probably other examples that are currently listed as Euceratherium (White et al. 2025). The metapodial anatomy is rather similar to the same bones of the takin (White et al. 2025), which is a Himalayan bovid that's kind of in-between things like muskox, sheep, and goats in appearance and habits. That may give an idea of what Speleotherium was doing. The short and stocky metapodials suggest it was active in rugged terrain, but based on fossil distribution it was not limited to higher elevations (White et al. 2025).

The skull in the process of being captured by photogrammetry (producing the 3D model linked above), showing its best side. Figure 36 in Kottkamp et al. (2020).

Given we're dealing with National Park Service fossils, you can imagine it's been on my radar. It showed up in the 2001 inventory of NPS cave fossils as what is now a grainy photo (Santucci et al. 2001), but we've since been able to feature the image in higher resolution glory for Carlsbad-specific inventories (Kottkamp et al. 2020, 2022). There's been a soft spot for it around here; it even got a coloring page, now part of the "Cenozoic Life in the National Parks" coloring book (just mentally substitute Speleotherium for Euceratherium as the label; the coloring page was prepared long before the bones got their new name).

References

Kottkamp, S., V. L. Santucci, J. S. Tweet, R. D. Horrocks, E. Lynch, and G. S. Morgan. 2020. Carlsbad Caverns National Park: Paleontological resource inventory (public version). Natural Resource Report NPS/CAVE/NRR—2020/2148. National Park Service, Fort Collins, Colorado.

Kottkamp, S., V. L. Santucci, J. S. Tweet, R. D. Horrocks, and G. S. Morgan. 2022. Pleistocene vertebrates from Carlsbad Caverns National Park, New Mexico. New Mexico Museum of Natural History and Science Bulletin 88:267–290.

Santucci, V. L., J. Kenworthy, and R. Kerbo. 2001. An inventory of paleontological resources associated with National Park Service caves. NPS Geologic Resources Division, Denver. Technical Report NPS/NRGRD/GRDTR-01/02.

White, R. S., J. I. Mead, and G. S. Morgan. 2025. Logan's austral scrubox, a new ovibovine (Mammalia: Artiodactyla: Bovidae) from Muskox Cave, Eddy County, New Mexico. New Mexico Museum of Natural History and Science Bulletin 101: 473–494.

Hyoliths VII: The New Blood

Have you ever been working on some mundane task when you suddenly wondered about the latest news from the world of hyoliths? Taking a walk, or merging onto a busy highway, or applying shampoo in the shower? All right, probably not, but if so, we're here for you!

Appropriately for this time of year, we have some news of hyoliths meeting or escaping grisly demises. (Or not, but that's taphonomy for you.) Kraft et al. (2023) published on an exceptionally well-preserved specimen of the Middle Ordovician central European trilobite Bohemolichas incola, including gut contents. The hyoliths are only a small part (quite literally!) of the story, which is well worth checking out if you have any interest in trilobites. The small trilobite (on the order of 35 mm or 1.4 inches long) apparently ate every darn thing it could fit in its mouth that wasn't putting up too much of a fight, including tiny hyoliths, ostracodes, stylophoran echinoderms, and chunks of shells.

The trilobite in question (Figure 1 from Kraft et al. 2023; scale bar 10 mm or 0.4 inches). Hyolith bits are in purple, including one recognizable shell under the trilobite's pygidium (tail segment). CC BY 4.0.

Paleozoic examples of the bilobed trace fossil Rusophycus are often attributed to resting trilobites, and one of the things you can do when you're not moving is pick up a snack. Lee et al. (2025), in a description of Cambrian Rusophycus from China, included an example where the trace was associated with hyolith shells. Unlike classic Rusophycus, thought to occur at the seafloor surface, this example was interpreted as a burrow. Also unlike classic trilobite predation trails, in this case the food had a hard shell. The trace-maker is thought to have been scavenging for hyoliths that had been transported from elsewhere.

Returning to the Ordovician of central Europe, we find a hyolith that was not eaten, although not from lack of trying. Fatka et al. (2023) reported a specimen of Elegantilites custos with healed damage in the form of scratches on its operculum. The culprit in this case is thought to have been an echinoderm, possibly an ophiuroid (brittle star) trying to get in.

Perhaps you'd prefer to think of your hyoliths more in terms of a grand and proud lineage, rather than delicious treats for every passing trilobite and brittle star. If so, Liu et al. (2024) have an analysis of Cambrian hyoliths for you. Using all valid Cambrian genera (N=115), they considered a set of 20 morphological characteristics over time and space. Overall hyolith taxonomic diversity peaked in Series 2 of the Cambrian (roughly speaking, the time when trilobites appeared and therefore kind of like the old "Early Cambrian"). They then keeled over sharply and were at lower levels for much of the rest of the Cambrian, locally reviving to a certain extent in the Early Ordovician. Their decline may have been due to an ocean anoxic event (the Sinsk Event) around 513 to 508 million years ago. The two major wings of hyoliths, the hyolithids (the kind with helens and complex opercula; filter feeders?) and orthothecids (the kind without helens and with simple opercula; deposit feeders?), did not follow the same curves: the orthothecids peaked sooner and felt the bite sooner, whereas the hyolithids didn't really get started until Series 2 and actually peaked just after it before suffering their drop. Morphological diversity was greatest in Series 2, although granted hyoliths had a somewhat limited repertoire.

The curve of Cambrian hyoliths. Figure 1 in Liu et al. (2024). CC BY 4.0.

References

Fatka, O., M. Valent, and P. Budil. 2023. The first healed injury in a hyolith operculum. The Science of Nature 110(50). https://doi.org/10.1007/s00114-023-01879-0.

Kraft, P., V. Vaškaninová, M. Mergl, P. Budil, O. Fatka, and P. E. Ahlberg. 2023. Uniquely preserved gut contents illuminate trilobite palaeophysiology. Nature 622: 545–551. https://doi.org/10.1038/s41586-023-06567-7.

Lee, D.-C., M.‑K. Oh, Y. Zhang, X.‑L. Zhang, J.‑H. Lee, K. Liang, and W. Li. 2025. Two new probable feeding traces of Rusophycus from the Cambrian of China: tracemaker’s behavior and formation mode. Geosciences Journal 29: 1–17. https://doi.org/10.1007/s12303-025-00007-6.

Liu, F., T. P. Topper, L. C. Strotz, Y. Liang, Y. Hu, C. B. Skovsted, and Z. Zhang. 2024. Morphological disparity and evolutionary patterns of Cambrian hyoliths. Papers in Palaeontology 10(2). https://doi.org/10.1002/spp2.1554.

Your Friends The Titanosaurs: Utetitan zellaguymondeweyae

Back almost four years ago when we first waded into Alamosaurus, I noted that "I was waiting on it because I was concerned that it might suffer a taxonomic detonation at any time, so I thought I'd hold off as long as possible." Titanosaurs work on their own schedule. Although people have danced around the issue for decades by suggesting that A. sanjuanensis is dubious or refraining from including some specimens in the species, nobody had taken the step of formally proposing another name for any of the material until Gregory S. Paul in October 2025 with Utetitan zellaguymondeweyae. This genus and species are based on the North Horn specimen that has long been the "practical purposes" type* of A. sanjuanensis.

*Seems like there ought to be a name for non-type specimens that everyone uses instead of the type. "Apatotype", for "deceptive type"? Or "pseudotype" for "false type"? Think like the "Mantel-piece" of Iguanodon mantelli. Brachiosaurus had a whole apatotype species until it was split off for Giraffatitan.

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.

More odds and ends

At the moment I'm preparing the grand annual update to The Compact Thescelosaurus. If you've been following along over the past couple of years, it doesn't take being Sherlock Holmes to guess what it will be. Actually, it doesn't even take being 1940s Radio Program Watson to guess, but do act surprised. In completely unrelated news, there's a taxon published this week I recommend you see: the little croc Thikarisuchus xenodentes. (What, you were expecting the theropod?) T. xenodentes, from the Cenomanian-age Blackleaf Formation of Montana, had a sharply triangular skull in top view and strongly differentiated teeth, among them the expected bitey teeth at the very front and long, low, narrow teeth at the back. This small croc may have had a taste for plants, or perhaps sliced up insects.

Something we love around here at Equatorial Minnesota is historical content about Minnesota geology. You may be familiar with the Minnesota Geological Survey's publication archive. It turns out that there are a bunch of MGS field notebooks scanned and available via the University of Minnesota libraries. You can find notebooks there from paleontologists such as Frederick Sardeson, Robert Sloan, and Clinton R. Stauffer, all of whom curiously have last names starting with "S". (Also interesting: Sardeson's field notebooks all have the left-hand pages filled out, but right-hand pages are much less frequently used. Was Sardeson a lefty?) There are also materials from the Department of Earth and Environmental Science.

Do you prefer to see your geology in the field? I came across a nice section of the St. Peter through Platteville under the I-94 bridge, on the east bank of the Mississippi. I'd been there years before but don't remember being so impressed with it. Maybe it wasn't as well-exposed then, or maybe I just wasn't experienced enough to appreciate it. The Platteville interval at the top was definitely exposed, but maybe this lower exposure is the result of more recent erosion or something. It definitely bears further photography and investigation, as it has a great view of the Glenwood.

The important part looks like this.

And here's what it looks like if I annotate all over it. I'm not entirely confident with the thickness of the Hidden Falls Member; for some reason the Mifflin is really grungy here. The Glenwood bits are open to interpretation (the Nokomis gets "Glenwood/St. Peter" because it's technically in the Glenwood but can't be distinguished from the St. Peter in well logs or gamma logs). The Tonti Member makes up most of the St. Peter Sandstone, if you're curious. There may be some Carimona at the very top. 

Oh yeah, also saw Bridal Veil Falls nearby, which has, y'know, seen better days, but is still running, after a fashion.

Or maybe you'd like some historical trivia? One of the things I wanted to find more about for the Mammoth Cave National Park paleo inventory was whatever became of the type specimen of Lithodrumus veryi, a Mississippian coral possibly collected from the park. It was described in 1904 by George Greene and the specimen has been lost to science since at least 1944. Greene's collection went first to the American Museum of Natural History and then to the National Museum of Natural History, but Lithodrumus veryi apparently went missing, as Easton (1944) couldn't find it at the AMNH. Just a few days ago I was looking up images of tabulate corals when I came upon a post at Louisville Fossils and Beyond that stated one cabinet had not been sold, and its contents were eventually going to the Indiana State Museum. Hope springs eternal! I've sent a message to the Indiana State Museum to see if perhaps L. veryi's type is there.

It's supposed to look like this (Greene 1904: Plate 49). Have you seen it, by any chance?

So that's what's going on around here. (Oh, that and some unusually intense bot "readership", or the whole of Hong Kong has suddenly discovered a passionate interest in the Ordovician fossils of Minnesota and Elliot Formation prosauropods. Maybe I'm cynical.) Tune in for the next post!

References

Allen, H. J., E. W. Wilberg, A. H. Turner, and D. J. Varricchio. 2025. A new, diminutive, heterodont neosuchian from the Vaughn Member of the Blackleaf Formation (Cenomanian), southwest Montana, and implications for the paleoecology of heterodont neosuchians. Journal of Vertebrate Paleontology e2542185. doi: https://doi.org/10.1080/02724634.2025.2542185

Easton, W. M. 1944. Revision of Campophyllum in North America. Journal of Paleontology 18(2): 119–132.

Greene, G. K. 1904. Contribution to Indiana palæontology 1(17): 168–175.

Whatever Happened to Euskelosaurus?

In principle, any dinosaur name considered dubious or a synonym can be brought back into use unless it is an objective junior synonym (based on the same specimen as a previous name) or suppressed by the International Commission on Zoological Nomenclature. In practice, some names are much more likely than others to rise out of the mire. For example, when was the last time you thought about Polyonax? (Is this the first time you've ever had occasion to think about Polyonax?) Then there are historical names based on questionable material that once were widely used but have now fallen completely out of favor. Think Monoclonius, Palaeoscincus, or Trachodon, long-time favorites that have staggered into obsolescence and cheap dinosaur toys.

Pulaosaurus qinglong

We're admittedly getting to Pulaosaurus qinglong a bit after announcement and description, but what's a few weeks after 160 million years? "Hypsil"-type dinosaurs are always going to be welcome here, and this one also has potential gut contents, albeit left for a later date, so let's extend a welcome and have a look after the jump break.