The Find

A weekend or so back I traveled down to Whitewater State Park to participate in their Fossil Field Trip event. As part of this, visitors go to a site off of the park where they can hunt for fossils (participants can keep two). It was very well presented and attended! The site is in the Cummingsville Formation, which is the limestone that follows the Decorah Shale. (Actually, it's a bit more complicated than that: much of the Cummingsville Formation in Olmsted County is roughly the offshore equivalent of the more nearshore Decorah of the Twin Cities, so where we were is probably equivalent to a horizon in the upper half of the Decorah quarry walls at the Brickyard.) Unlike the distinctive green-gray Decorah, the Cummingsville presents as a tan unit. It's a shaly limestone at the site, so it doesn't quite have the strength of a pure limestone, but it does better than the Decorah.

Weathering Cummingsville at the site.

The Cummingsville is not as fossiliferous as the Decorah, even accounting for my different search image, and the site is a known fossil site, so the going was slow at the beginning. Then I found this:

Well, I did do a little prep work and applied water before taking this picture, and the rock is about palm-sized all told, but you get the idea.

I'd been hoping to find a receptaculitid, because those are common in the Cummingsville and I haven't found one, but this was something better. Even in an unprepared state it was obviously an echinoderm based on the plates, but what kind? A crinoid calyx? Something else?

If you know what the arrows are pointing to...

The prep work exposed the little vent-like features, meaning it was some kind of rhombiferan cystoid. The cleaning also made it more obvious where the plates met, which can be kind of confusing when there are all these ridges to mislead the eye.

A handy diagram! The dotted lines are where the plate edges become obscure or are lost.

If you don't know what it is, check this out:

Figure 1 from Parsley (1970), with red lines and dots added by me. Original image CC BY-NC-SA 3.0.

Yup, this is a Pleurocystites, or at least a good-sized chunk of one. Either P. squamosus (Parsley 1970) or P. strimplei (Brower 1999) would be appropriate for the Cummingsville; there's not really enough there to tell between them, but I'm not complaining! It's fun to be in the right place at the right time with the right knowledge and experience.

References

Brower, J. C. 1999. A new pleurocystitid rhombiferan echinoderm from the Middle Ordovician Galena Group of northern Iowa and southern Minnesota. Journal of Paleontology 73(1): 129–153. 

Mossler, J. H. 2008. Paleozoic stratigraphic nomenclature for Minnesota. Minnesota Geological Survey, St. Paul, Minnesota. Report of Investigations 65.

Parsley, R. L. 1970. Revision of the North American Pleurocystitidae (Rhombifera-Cystoidea). Bulletins of American Paleontology 58(260): 135–213. 

The Continuing Story of Nanosaurus agilis

Recently Barrett and Maidment (2025) published a paper on the state of Morrison hypsilophodont-things, which is of great interest here because after two long posts on Nanosaurus agilis, we're solidly invested in its fate. How did it fare? Short answer: not very well. But, on the other hand, neither did anybody else. Well, Drinker was shown more appreciation than probably anyone has given it since 1990, but that's not saying much.

So, what to call these happy fellows at the Denver Museum of Nature and Science?

Barrett and Maidment (2025) went over the type specimens of N. agilis, N. rex (Othnielia), Laosaurus celer, L. consors (Othnielosaurus), L. gracilis, and, via illustrations, Drinker nisti. (There is a slight advance on Carpenter and Galton 2018, in that we now get the implication that Bob Bakker has D. nisti as opposed to the whereabouts being unknown.) They find none of the type specimens to be diagnostic. The one that comes off the worst is L. consors. Material cataloged as the type is an assemblage rather than an individual. To be fair, Marsh knew he had multiple individuals at the time, but then he should have been more careful about specifying a type. The parts that had been on display as a panel mount at Yale may be one associated individual, consisting of most of the cervical and dorsal series (just centra), possibly six sacrals, parts of the left shoulder girdle and the pelvis, a partial left femur and complete left foot, and parts of the right femur, tibia, and astragalus. This is a lot of parts/partials plus a lot of plaster, which is not encouraging. The rest of the material is a chimeric mix including at least juvenile dryosaur and hypsil material. The only one of the six that ends up being interesting is D. nisti, which has some dental and jugal features reminiscent of pachycephalosaurs (but is still not diagnostic, although it would be nice to have the type material in hand to be sure).

Where does this leave the Morrison hypsil(s), which Carpenter and Galton (2018) had declared N. agilis? Anonymous, for the time being. Carpenter and Galton (2018) looked upon the pile of Morrison hypsil bits and proposed it was "all" Nanosaurus agilis. Barrett and Maidment (2025) looked upon the same pile and clutch of names and regarded it as a taxonomic dead end, to be set aside to allow a fresh start for more complete and better preserved specimens (with quarry maps and documented associations and such).

At heart, we're seeing two different approaches to taxonomy, and which one you choose depends on how pragmatic you are and how bound you feel by existing names. If you want a species with a holotype featuring robust apomorphies, N. agilis is not for you. We saw that in the comments section of the last post: most of the characters cited by Carpenter and Galton (2018) are widely distributed among hypsil-things, with just a couple that might have some particular use. However: Is there a hypsil-thing in the Morrison that is anatomically consistent across specimens, whether or not said specimens are diagnostic across Ornithischia? If so, is it reasonable to call this hypsil *something*, knowing that it may be revised later? If so, the oldest existing name is Nanosaurus agilis. If you go that route, I'd recommend looking into a neotype, though. ("All would be well, if, if, if, if, if...")

References

Barrett, P. M., and S. C. R. Maidment. 2025. A review of Nanosaurus agilis Marsh and other small-bodied Morrison Formation “ornithopods". Bulletin of the Peabody Museum of Natural History 66(1): 25–50. doi: https://doi.org/10.3374/014.066.0102.

Carpenter, K., and P. M. Galton. 2018. A photo documentation of bipedal ornithischian dinosaurs from the Upper Jurassic Morrison Formation, USA. Geology of the Intermountain West 5:167–207. doi:

The downside of reef building?

I was reviewing text for a website a few weeks back dealing with aspects of the history of life, and a couple of things struck me about biological reefs. First, a quick look at reef-builders through time (a useful overview can be found here if you'd prefer more flesh on the bones, or corallites or shells or whatever may be more appropriate):

The first multicellular reef-builders were the archaeocyathan sponges, who flourished briefly in the Cambrian but did not even make it to the end of the period. Corals, in the form of rugose and tabulate corals, spread in the Ordovician but took a while to make reefs. They were joined by stromatoporoid sponges (layered like stromatolites, spelled like stromatolites, but not stromatolites) and various microbes, with the Devonian being an apex of reef-building. The classic stromatoporoid-tabulate reefs of the Devonian went kaput in the End-Devonian extinction. Permian reefs were a conglomeration of just about everything that couldn't get out of the way: various algae, sponges, bryozoans, and other less obvious things. This assortment bought it at the end of the Permian. False starts with scleractinian corals in the first part of the Mesozoic gave way to the rudist bivalves in the Cretaceous. The rudist reefs went out with non-avian dinosaurs, marine reptiles, pterosaurs, ammonites, and so forth at the end-Cretaceous extinction. Finally we get to the big scleractinian coral reefs in the Cenozoic, with some sponge and oyster reefs and such for variety.

So far, a typical pattern: group of organisms branches into reef building, reefs spread and become ecologically complex, reefs flourish for a while, mass extinction wipes out reefs. Then after a hiatus reefs become fashionable again, with some other group laying the foundation for a new iteration, and the cycle continues. A couple of observations come to mind. First, reefs seem to be an obvious evolutionary path for immobile marine invertebrates. It may take some time, but some group always takes up the baton after another falters.

Then, the other shoe. What happens to the previous reef-builders? Seen any archaeocyaths lately? Any vacation packages advertising stromatoporoid reef visits for their island getaways? Run across any rudists while snorkeling? Could it be that once a group goes all-in on the reef habit, it's stuck with it?

Furthermore, reefs have a habit of getting smacked in mass extinction events. Does a reef inherit a narrowing range of environmental restrictions from its components as its complexity increases? Does it become vulnerable to unpredictable instability, such as some minor constituent going through a bad patch leading to collapse via a Rube Goldbergian-cascade of events? More broadly, does reef building amount to an evolutionary Faustian bargain, in which a group becomes dominant for a while by locking itself into a doomed arrangement? (Granted, we're all doomed in the final analysis, but some of us are more obviously doomed than others.) Or am I just playing the gloomy Minnesotan?

Arcola Bluffs Day Use Area

It's been a good while since our last St. Croix post, hasn't it? I wanted to let you in on a fun place I recently visited for the first time; Arcola Bluffs Day Use Area. This site is not widely known; there's this article (with much more artistic photos than my own), an NPS cultural landscape assessment from 2018 that weighs in at 204 mb (NPS 2018; absolutely worth it if you want a thorough understanding of the site, and also includes a section on Fairy Falls), and then some short pieces here and there, and that's about it. Visiting it, though, you'll discover great geology, views of the river and the historic Soo Line High Bridge, forest and prairie settings, and some evocative ruins.

Titanosaur osteoderms, 2025 update

Occasionally I glance at the site statistics, but since I don't use anything detailed there's not a lot to get from them except that it's fun to see where the obvious spoof hits are coming from (Singapore, lately; sometimes Hong Kong or Russia). Sometimes I can tell that a post has been picked up elsewhere and gotten a few views. Over the last month or so, there have been an unusually large number of visits to "Titanosaur osteoderms: functions and conclusions", and at the same time a similar number of visits have come from a service at the University at Buffalo. Conclusion? Seems like someone at the university is using the post in a course. If that's what's going on, this one is for you!

Since I wrote the osteoderm series back in 2019, there have a few reports of interest on titanosaur osteoderms. I added several overlooked and new records to the distribution post in 2019–2020, and there hasn't been much change there since. One tangential note, also applicable to "Titanosaurs of Yesterday", is a further advance in the study of Agustinia ligabuei, the spiky sauropod that wasn't. Bellardini et al. (2022) published an analysis that found A. ligabuei was not a titanosaurian or even a macronarian, but a rebbachisaurid. (And it's still not armored, either.)

As noted in the Menucocelsior arriagadai post, Rolando et al. (2022) was not just a description of a new titanosaur taxon, but also included reports of material from other titanosaurs. Among these specimens were four isolated osteoderms from the Cerro Matadero site of the Allen Formation. Three represent the "ellipsoidal" form (bulb-and-root) of D'Emic et al. (2009) and the other is a "keeled" osteoderm. Rolando et al. interpreted the keeled osteoderm as perhaps from the tail or back of a saltasaur and the two more complete ellipsoidal osteoderms as perhaps aeolosaur osteoderms from the hip region.

Another report also discussed in another post is Fronimos (2021) on an osteoderm of a Big Bend titanosaur (e.g., Big Bend Alamosaurus). To paraphrase, this is a large oval and unkeeled osteoderm from the upper Javelina. It is tall, symmetrical, 19.9 cm long (7.83 in), not hollow, not differentiated into a bulb and root, and does not have a cingulum. It resembles the North Horn Formation Alamosaurus osteoderm and the osteoderms of Mendozasaurus neguyelap and unnamed South American forms (Fronimos 2021). Fronimos (2021) regarded the most likely functions as mineral storage, local defense, and display.

Concerning the function of titanosaur osteoderms, Silva Junior et al. (2022) published a study using finite element analysis to evaluate titanosaur osteoderms versus likely titanosaur adversaries, specifically the bites of abelisaurs and baurusuchid crocs. They found that bites had less of an effect on solid osteoderms (i.e., those without hollow internal spaces), and interpreted this to indicate that solid osteoderms could do more than provide mineral storage. On the other side of the mineral storage question, Broeckhoven and du Plessis (2022) made an analysis of osteoderms in armadillo lizards. Using micro-computed tomography, they found that the female lizards in their study had denser, more compact osteoderms than males, and observed the presence of TRAP-positive cells (tartrate-resistant acid phosphatase, involved in bone resorption and breakdown). Denser osteoderms may help maintain a minimum level of mineral density for reproduction and provide defensive strength to osteoderms also being used for a mineral storage function. The authors did not find a difference in density between seasons, and suggested this meant the osteoderms were only subject to resorption during particularly stressful conditions, or that it only took place during certain phases of embryo growth. They concluded that mineral storage for reproduction is a plausible function for osteoderms in female reptiles.

Finally, I've saved the most interesting update for last. In an abstract, Filippi et al. (2023) described an articulated tail, MAU-Pv-CO-726, from the Bajo de la Carpa Formation of Cerro Overo–La Invernada, Patagonia, Argentina. (Yes, another Bajo de la Carpa mystery titanosaur!) MAU-Pv-CO-726 includes 25 caudals, 11 chevrons, and two osteoderms in place, with another nearby. The pair of osteoderms is associated with the last anterior caudal, found flanking the side and underside of the tail (about where the chevron articulates with the caudal). They are described as bulbous, oval, a little more than 10 cm (4 in) long, and feature a medial ridge and tapered spine on the lateral half, whereas the solitary osteoderm is described more like a classic bulb-and-root. Filippi et al. found MAU-Pv-CO-726 to be the sister taxon of Rinconsaurus caudamirus, marking the first evidence of an armored rinconsaur (and no doubt causing R. caudamirus's usual best friend Muyelensaurus pecheni great phylogenetic distress). They interpreted the location of the osteoderms as evidence of a defensive function. The osteoderms' placement also has implications for paleoart; titanosaur restorations usually put osteoderms on upper-lateral surfaces. But, then again, if you want my opinion I think titanosaurs were too diverse for a one-size-fits-all approach to osteoderms, in function, anatomy, or placement.

References (note that a couple are different from previous usage, as those were online preprints)

Bellardini, F., R. A. Coria, G. J. Windholz, A. G. Martinelli, and M. A. Baiano. 2022. Revisiting the Early Cretaceous sauropod Agustinia ligabuei (Dinosauria: Diplodocoidea) from southern Neuquén Basin (Patagonia, Argentina), with implications on the early evolution of rebbachisaurids. Historical Biology 35(12): 1–27. doi: https://doi.org/10.1080/08912963.2022.2142911

Broeckhoven, C., and A. du Plessis. 2022. Osteoderms as calcium reservoirs: Insights from the lizard Ouroborus cataphractus. Journal of Anatomy 241(3): 635–640. doi: https://doi.org/10.1111/joa.13683

D'Emic, M. D., J. A. Wilson, and S. Chatterjee. 2009. The titanosaur (Dinosauria: Sauropoda) osteoderm record: review and first definitive specimen from India. Journal of Vertebrate Paleontology 29(1):165–177.

Filippi, L. S., F. Bellardini, A. Paulina-Carabajal, P. Cruzado-Caballero, J. González-Dionis, A. H. Méndez, F. Gianechini, K. Ulloa-Guaiquin, A. Garrido, I. Maniel, Y-N. Lee, and K. Do-Kwon. 2023. Articulated osteoderms on a titanosaur tail from Cerro Overo–La Invernada (Bajo de la Carpa Formation), Upper Cretaceous, Northern Patagonia Argentina: Paleobiological and paleoecological implications. Publicación Electrónica de la Asociación Paleontológica Argentina 24(R3): R67–R68.

Fronimos, J. A. 2021. Morphology and neurovascular anatomy of a titanosaur (Dinosauria, Sauropoda) osteoderm from the Upper Cretaceous of Big Bend National Park, Texas. Cretaceous Research 120: 104670. doi: https://doi.org/10.1016/j.cretres.2020.104670

Rolando, M. A., J. A. Garcia Marsà, F. L. Agnolín, M. J. Motta, S. Rozadilla, and F. E. Novas. 2022. The sauropod record of Salitral Ojo del Agua: An Upper Cretaceous (Allen Formation) fossiliferous locality from northern Patagonia, Argentina. Cretaceous Research 129: 105029. doi: https://doi.org/10.1016/j.cretres.2021.105029

Silva Junior, J. C. G., F. C. Montefeltro, T. S. Marinho, A. G. Martinelli, and M. C. Langer. 2022. Finite elements analysis suggests a defensive role for osteoderms in titanosaur dinosaurs (Sauropoda). Cretaceous Research 129: 105031. doi: https://doi.org/10.1016/j.cretres.2021.105031

Recent NPS paleontological inventories

I haven't posted as much on my National Park Service projects over the past couple of years, in part because I don't want to accidentally reveal sensitive locality information and in part because much of what I've done in that time frame doesn't lend itself to a blog format. As anyone who's worked somewhere long enough can tell you, eventually your duties start creeping toward management. It's very important to do things like coordinate reviews, provide feedback, maintain archives and data, and otherwise keep things going as smoothly as possible, but they make for dry posts. To make up for it and show off some the work we've been doing, I'm going to briefly highlight our most recent park inventories, which all have public versions available.

Over the past year, we've published five park-level inventories, as both sensitive versions (internal-NPS only, with detailed locality information) and public versions. Lead authorship for these five includes park staff, a Scientists in Parks participant, a team of subject-matter experts, and in one case myself. I'm unofficial editor-in-chief for the Paleontology Program and have been intimately involved in getting these to publication, including taking care of aspects such as formatting, styles, copy-editing, and overall consistency among reports. Park-level inventories are intended for a park audience first, so we try to avoid jargon or make sure it is defined. In days past these were published as physical copies, but they are essentially digital now, which helps with the inclusion of more figures. I'm a big advocate of lots of photos, to help park staff identify types of fossils (and things that aren't fossils!).

The group of five from 2024–2025 runs a broad gamut of geography, geologic time, and types of fossils. Digital copies can be found at the NPS's DataStore on IRMA (Integrated Resource Management Applications) and the outside website National Park Service History Electronic Library & Archive. (Both sites are also fun to search in general if you have any interest in parks!) Full citations are provided in the references at the end, with the IRMA link as the DOI and the NPS History link under the title (direct pdf link).

Bryce Canyon National Park

Bryce Canyon National Park in southern Utah is famous for its scenery, which is weathered out of the colorful strata of the Paleogene Claron Formation. The Claron, though, is rather limited for fossils unless you like terrestrial snails or insect burrows. Instead, Bryce Canyon's best fossils come from the Upper Cretaceous Straight Cliffs–Wahweap sequence, which is notable because these strata slot into part of what is otherwise a rough 20–25 million years for terrestrial fossils in North America (about 100 to 75 Ma). Those of you familiar with the Cretaceous of North America know what happened in that time frame: the choice terrestrial depositional basins decided to take up snorkeling for an extended period. It has only been in the past few decades that a solid fossil record has been found for some of this gap. The Straight Cliffs Formation is good for vertebrate microfossils, and there are several such localities in Bryce Canyon. In fact, the paleontological inventory was begun in a roundabout way due to microfossils, following emergency monitoring and salvage efforts at microfossil sites on an area of road work. The resurgence of interest in fossils at the park led to an impressive field-based survey by a team of park staff and Scientist in Parks participants in 2022 and 2023 that was documented in Tran et al. (2024).

Colorado National Monument

Colorado National Monument in western Colorado is right outside of classic Morrison Formation collecting areas (the type locality of Brachisaurus altithorax among them). There is a history going back to the 1970s of paleontological inventories documenting aspects of the monument's fossils, such as the Morrison Formation or sites in the vicinity of trails. In 2023, Scientist in Parks participant Austin Shaffer spent a nine-month term investigating the sites found in the previous inventories and looking for new sites (Shaffer et al. 2024a). The monument was already known as a place with notable terrestrial trace fossils, but Austin turned up an outstanding variety of tracks, principally in the Morrison Formation and the Naturita Formation (formerly known as the Dakota Formation in this area). The new Morrison Formation tracks are notable because they appear to include both stegosaur and ankylosaur tracks, while the Naturita Formation wasn't even known to be fossiliferous in the monument before. In between, the Burro Canyon Formation (roughly equivalent to the Cedar Mountain Formation of Utah) has some uncommon bone material attributed to a sauropod, the catch being it's in a blastedly hard conglomeratic sandstone.

Cuyahoga Valley National Park

Turning eastward, Cuyahoga Valley National Park in northeastern Ohio is a little like Mississippi National River and Recreation Area in the Twin Cities, as a river-centered park unit with Paleozoic bedrock situated in an urban area. Here we're mostly looking at the Devonian and Mississippian. Sporadic reports of fossils have been made here since the 19th century, and one of our partners (J.-P. Hodnett) made a paleontological reconnaissance in 2022, but a systematic investigation of the area had never been done. We were impressed with Austin's work on the Colorado National Monument inventory and wanted to get him on another project, and the Cuyahoga project came together in the summer of 2024 (Shaffer et al. 2024b). This time there were no dinosaurs (which would have been rather surprising!), but in addition to the expected Devonian–Mississippian marine invertebrates there was scrappy plant material, a likely eurypterid, and a fragment of a possible Mississippian tetrapodomorph jaw. There is also a partial skeleton of a heretofore-undescribed Devonian ctenacanth shark that was found back in the 1930s.

Effigy Mounds National Monument

Effigy Mounds National Monument in northeastern Iowa was a park unit that had long been on my radar because of its bedrock geology: Jordan Sandstone up to the Dunleith Formation. I got the opportunity in 2023 to spend some time on the ground there and was rewarded with the discovery of a healthy assortment of Platteville Formation fossils (left in place!). More than two dozen taxa could be distinguished, mostly brachiopods and snails (Tweet and Santucci 2025). I also turned up an unexpected earliest reference to fossils in what is now the monument: as part of David Dale Owen's survey of the region, Benjamin Shumard stopped by in 1848 and recorded gastropods in what we would now call the Prairie du Chien Group (named for Prairie du Chien, Wisconsin, right across the river).

Mammoth Cave National Park

Mammoth Cave National Park's report is the most recent to be published, but preliminary work toward it began in 2019, making this our project with the longest gestation to date. Why so long? Well, for one thing it's essentially an edited volume with eight fully developed separate topical inventories: history of work, geology, Paleozoic plants, Paleozoic invertebrates and ichnofossils except for echinoderms, Paleozoic echinoderms, Paleozoic vertebrates, Quaternary vertebrates, and paleontological resource management and similar topics. Each had its own authorship group of subject-matter experts (except for the one on invertebrates and ichnofossils, which was done by some guy who mostly knows the Ordovician of Minnesota), and each had its own review process. Furthermore, the teams working to locate fossils are very, very good at doing so, so we kept on (keep on!) getting new information. Finally, at the beginning of 2024 the publication office made substantial changes to how they wanted submissions to be set up, then revised the new version, and as you might imagine it can be an interesting challenge to make changes to a document that is on the order of 450 pages long with nearly 200 figures. So, it took a long time, but I think the results are absolutely worth it.

References

Shaffer, A. B., J. S. Tweet, and V. L. Santucci. 2024a. Colorado National Monument: Paleontological resource inventory (public version). Science Report NPS/SR—2024/116. National Park Service, Fort Collins, Colorado. https://doi.org/10.36967/2303613

Shaffer, A. B. , V. L. Santucci , J. S. Tweet , and J.-P. M. Hodnett. 2024b. Cuyahoga Valley National Park: Paleontological resource inventory (public version). Science Report NPS/SR—2024/210. National Park Service, Fort Collins, Colorado. https://doi.org/10.36967/2306411

Tran, T., A. E. Bonham, J. S. Tweet, and V. L. Santucci. 2024. Bryce Canyon National Park: Paleontological resource inventory (public version). Science Report NPS/SR—2024/123. National Park Service, Fort Collins, Colorado. https://doi.org/10.36967/2303710

Toomey, R. S., J. S. Tweet, and V. L. Santucci , editors. 2025. Mammoth Cave National Park: Paleontological resource inventory (public version). Science Report NPS/SR—2025/243. National Park Service, Fort Collins, Colorado. https://doi.org/10.36967/2308547

Tweet, J. S., and V. L. Santucci. 2025. Effigy Mounds National Monument: Paleontological resource inventory (public version). Science Report. NPS/SR—2025/230. National Park Service. Fort Collins, Colorado. https://doi.org/10.36967/2307451

Your Friends The Titanosaurs: Chadititan calvoi

No sooner do I finish one titanosaur post when another new one shows up for its turn in the spotlight. Our latest guest, Chadititan calvoi, is another from the hallowed titanosaur stomping grounds of Late Cretaceous Patagonia. For anyone who feels the need to chuckle over the meme factor in the name, the jump break should present an opportunity to get it out of the system. (Ironically enough, Chadititan is noted for its small body size and slender limbs.) If you don't know the meme, feel free to ignore it and cross the jump break just the same.