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.

Your Friends The Titanosaurs: Petrustitan hungaricus and Uriash kadici (and every other Transylvanian titanosaur)

It's been a while since I got to do one of these...

To say that Díez Díaz et al. (2025) names Petrustitan hungaricus and Uriash kadici is to miss the point. Between the paper itself and the supplementary material, you get a novel's worth of information on the titanosaurs of Romania, including descriptions of a couple dozen significant finds (including individuals and assemblages of multiple individuals). But yes, the report does name one new genus and species, and transfers another species to a second new genus.

Happy Valentine Formation Day!

With Valentine's Day having come on Friday, I thought it would be fun to show some love to the Valentine Formation. This geologic unit, from the Middle Miocene of Nebraska, is a great fossil producer but not especially famous, so let's give it a moment in the spotlight.

On fossils in metamorphic rocks

One of the introductory-level bits of information people learn about fossils is that fossils are found in sedimentary rocks, not igneous rocks or metamorphic rocks. This works as a first-order approximation, but... it's not strictly true. For example, among igneous rocks, there are some that overlap sedimentary rocks, e.g., pyroclastic flows, ash beds, and so on. You can certainly find fossils in those. There are also occasional impressions of things in basalt flows; tree trunk molds are most common, and at least one rhino (the famous "Blue Lake rhino"; e.g., Beck 1937) has been captured this way. Tree molds are also interesting for testing our conventional definitions of paleontology in other ways: Because of the rapid cooling and hardening of the basalt, tree molds are essentially instant fossils. The rock can't get much more lithified, after all (especially compared with Quaternary sedimentary slop), yet modern examples haven't put in the time that frequently quoted definitions insist on for fossils, such as 10,000 years. In my day job we talk about paleontological resources as evidence of life in a geological context, so there is no cutoff. Where was I? Oh, yes. Basically, you can get fossils in igneous rock if the rock was playing by sedimentary rules when it formed. Don't expect them in intrusive igneous rocks, though, except in xenoliths of sedimentary host rock (e.g., McCracken et al. 2000, also featuring cores!).

For metamorphic rocks, most of us with paleontological experience will make exceptions for low-grade metamorphics: quartzites, slates, low-grade marbles, things like those. In fact, a lot of rocks commonly called "marbles" are just limestones that can hold a polish. Get much beyond that, and surely the temperature, pressure, chemically active fluids, and mineralogical changes will destroy any unsuspecting crinoid or brachiopod, right?

Well...

Obviously, the answer is "not always", otherwise there wouldn't be a post.

Reports of fossils in metamorphic rocks even as far gone as eclogite (Cavrgna-Sani et al. 2010) or migmatite (Hill 1985; the rock you get when it stops screwing around with metamorphism and gets down to serious melting, but doesn't finish) pop up every so often in the literature as a thin thread of geological quasi-Forteana. The "thin thread" is because they are not common. If they *were* common, they wouldn't be worthy of comment. You don't get a paper out of announcing that there are crinoid columnals in the Decorah Shale. Bucher (1953) is perhaps the most significant reference on the subject, and includes a good bibliography, but through no fault of its own is now more than 70 years old and likely to only get older. Labora-López et al. (2015) adds a few more recent references in its discussion, although it has its own purposes that do not include being a thorough review and update of Bucher (1953).

Aside from being a curiosity, fossils in metamorphic rocks are useful for providing age controls that are notoriously absent from many metamorphic units, and sometimes can help with correlations. Other interpretations are limited by distortion or general poor preservation of the fossils, and by the topic of Labora-López et al. (2015), the loss of information from the sedimentary matrix itself.

One interesting aspect evident from Bucher's lists is that the fossils are not necessarily confined to animals with hard parts that are particularly resistant to replacement (e.g., crinoids). There are recrystallized bivalves, for example. Of course, bivalve replacement is hardly unusual in itself, as shells of bivalves and other mollusks are prone to replacement anyway thanks to the poor stability of aragonite over geologic time, which is why their fossils are so often molds and casts. Some fossils have been replaced by more exotic materials, including echinoderm ossicles replaced by diopside and epidote in a contact metamorphism zone.

Why have fossils in metamorphic rocks not attracted much attention? A not-insignificant part of the problem is people haven't generally been looking for them. As noted by Bucher (1953), paleontologists weren't looking because they assumed that metamorphism destroyed fossils, metamorphic rocks are a pain in the neck to work with compared to sedimentary rocks, and the fossils that have been found in metamorphic rocks are not of great quality, so why bother? Meanwhile, the hard-rock specialists weren't looking because they were hard-rock specialists and weren't interested in fossils.

Still, though, even if this means that fossils are actually some order of magnitude more abundant in metamorphic rocks than generally thought, they aren't exactly falling out of schists and gneisses. Bucher had an elegant proposal: he suggested that most metamorphic rocks of appropriate age to have fossils of things like brachiopods, crinoids, and mollusks are derived from rocks that were deposited in settings with few fossils to begin with. The exact language used is more complicated and bound up in pre-plate-tectonic thought and geosynclines (well, it was 1953, after all), but you get the point: It's hard to have metamorphosed fossils if you don't have fossils to start with. Another rule of thumb Bucher proposed is that fossils can persist if metamorphism does not involve mechanical effects and the fossils are much larger than the size of newly formed minerals. The chances aren't great, but if you're face to face with a metamorphic rock that began as a sedimentary rock of Phanerozoic age, there might just be a stubborn brachiopod or crinoid in there.

References

Beck, G. F. 1937. Remarkable west American fossil, the Blue Lake Rhino. The Mineralogist 5(8): 7–8, 20–21.

Bucher, W. H. 1953. Fossils in metamorphic rocks: a review. Bulletin of the Geological Society of America 64: 275–300.

Cavargna-Sani, M., J. L. Epard, and W. L. Taylor. 1997. Discovery of fossils in the Adula nappe, new stratigraphic data and tectonic consequences (Central Alps). Bulletin de la Société vaudoise des Sciences Naturelles 92: 77–84.

Hill, M. L. 1985. Remarkable fossil locality: crinoid stems from migmatite of the Coast plutonic complex, British Columbia. Geology 13: 825–826.

Laborda-López, C., J. Aguirre, and S. K. Donovan. 2015. Surviving metamorphism: taphonomy of fossil assemblages in marble and calc-silicate schist. PALAIOS 30: 668–679.

McCracken, A. D., D. K. Armstrong, and T. E. Bolton. 2000. Conodonts and corals in kimberlite xenoliths confirm a Devonian seaway in central Ontario and Quebec. Canadian Journal of Earth Sciences 37(12): 1651–1663.

Journey Somewhat Nearer to the Center of the Earth: fossils in cores

Most of the time, when people are looking for fossils, they find them at the surface or just below. However, this is hardly the limit of where they can be found. After all, a fossiliferous formation found at the surface in one location may be buried hundreds to thousands of feet beneath other rocks and sediments somewhere else, and it doesn't stop being fossiliferous just because it's buried that far down. It just becomes much less accessible. We can get glimpses of the buried fossils through core samples.