Your Friends The Titanosaurs: Mesetasaurus protector (plus news from Antarctica)

The newest titanosaur is the second from Uruguay and the Guichón Formation. Here's the breakdown:

Genus and Species: Mesetasaurus protector. The genus name is a reference to the locality, Meseta de Artigas. The species name is a reference to the Uruguayan national hero José Artigas, (Soto Núñez et al. 2026). His name is also part of the locality, so we end up with a multilayered reference that boils down to "José Artigas's lizard".

Citation: Soto Núñez, M., F. Montenegro, and D. Perea. 2026. A new aeolosaurini (Sauropoda, Titanosauria) from the Upper Cretaceous of Uruguay. Ameghiniana (advance online publication). doi: https://doi.org/10.5710/AMGH.19.06.2026.3689

Geography and Stratigraphy: The type and only known specimen is from Meseta de Artigas, in the northern part of Paysandú Department, Uruguay. We are in the Guichón Formation, previously noted as the source of the titanosaur Udelartitan celeste (Soto et al. 2024). At that time, an age in the first half of the Late Cretaceous was suggested. This time a somewhat younger age is proposed, "perhaps late Santonian-early Campanian" (Soto Núñez et al. 2026).

Holotype: FC-DPV 3740 (Vertebrate Fossil Collection, Facultad de Ciencias, Universidad de la República), two anterior caudals (Soto Núñez et al. 2026). The authors refer to the more anterior caudal as 3740A and the more posterior as 3740B, and suggest A is the third caudal and B is the sixth.

The two caudals are well-preserved, although unfortunately this is not the same as completeness (the processes are truncated). They are distinct from those of U. celeste, being decidedly aeolosaurine/id/inid in anatomy. They are also somewhat smaller, not that U. celeste was an especially titanic titanosaur in the first place. Not surprisingly given its anatomy, M. protector plots among the aeolosaurs, making it the second record of an Uruguayan aeolosaur after the Asencio Formation caudal in Soto et al. (2022).

I don't have a whole lot to say about this species. To make this post a little less perfunctory, I'd like to go a little farther south. Barrett et al. (2026) have reported the second titanosaur from Antarctica, after the caudal reported by Cerda et al. (2011, 2012). The new material is BAS D.8621.25 (British Antarctic Survey, Cambridge, United Kingdom), a partial anterior caudal that coincidentally enough also has a bit of an aeolosaur appearance. It comes from the early Campanian-age Beta Member of the Santa Maria Formation on James Ross Island. (For those of you keeping track, Cerda et al. also described their specimen, a partial middle caudal, from the Santa Maria Formation. The particular strata have since been placed in the overlying Snow Hill Formation as the Gamma Member.) It is not well preserved and is rather small, at only 59 mm (2.3 in) long, 89 mm (3.5 in) if you include the substantial posterior condyle. This puts it in the company of Magyarosaurus dacus. We can't be sure of the exact growth stage, but there's enough of the neural arch to show it wasn't a very young juvenile. Interestingly, although not described until now, BAS D.8621.25 is actually the first classic dinosaur fossil collected from Antarctica, way back in December 1985 (Barrett et al. 2026).

Several views of BAS D.8621.25. Figure 3 in Barrett et al. (2026). CC-BY-4.0.

References

Barrett, P. M., P. D. Mannion, S. L. Beeston, M. C. Lamanna, B. Clark, A. Otero, J. P. O’Gorman, and M. Evans. 2026. A titanosaurian sauropod dinosaur from the Upper Cretaceous of Antarctica. Acta Palaeontologica Polonica 71(2): 349–362. doi: https://doi.org/10.4202/app.01315.2025.

Cerda, I., A. Paulina Carabajal, L. Salgado, R. Coria, and J. J. Moly. 2011. The first record of sauropod dinosaurs from Antarctica. Journal of Vertebrate Paleontology, Program and Abstracts, 2011:86.

Cerda, I. A., A. Paulina Carabajal, L. Salgado, R. A. Coria, M. A. Reguero, C. P. Tambussi, and J. J. Moly. 2012. The first record of a sauropod dinosaur from Antarctica. Naturwissenschaften 99:83–87. 

Soto, M., F. Montenegro, F. Mesa, and D. Perea. 2022. Sauropod (Dinosauria: Saurischia) remains from the Mercedes and Asencio formations (sensu Bossi, 1966), Upper Cretaceous of Uruguay. Cretaceous Research 131:105072. doi: https://doi.org/10.1016/j.cretres.2021.105072. 

Soto, M., J. L. Carballido, M. C. Langer, J. C. G. Silva Junior, F. Montenegro, and D. Perea. 2024. Phylogenetic relationships of a new titanosaur (Dinosauria, Sauropoda) from the Upper Cretaceous of Uruguay. Cretaceous Research 105894. doi: https://doi.org/10.1016/j.cretres.2024.105894.

Soto Núñez, M., F. Montenegro, and D. Perea. 2026. A new aeolosaurini (Sauropoda, Titanosauria) from the Upper Cretaceous of Uruguay. Ameghiniana (advance online publication). doi: https://doi.org/10.5710/AMGH.19.06.2026.3689.

Your Former Friends The Ex-Titanosaurs

If you frequent The Compact Thescelosaurus, you may have noticed that several sauropods formerly placed in Titanosauria have been reclassified. (Apropos of nothing, I often wonder what the people who are browsing the sheets think when they see me active. Do they get excited to see what I'm working on? Or is it an inconvenience to whatever searching or sorting they're doing? Sometimes more appear while I'm working. I know it's just a coincidence, but it amuses me to think there's some kind of alert I don't know about that is issued when I show up.) This is not the first time this has happened. Back in 2019 Mannion et al. (2019) led me to move Baotianmansaurus henanensis and Dongyangosaurus sinensis to Titanosauria? (the question mark, the second-to-last refuge of a coward) and Jiangshanosaurus henanensis and Yongjinglong datangi out of Titanosauria altogether. After Beeston et al. (2024), the diamantinasaurs were also put at Titanosauria?. There has now been another purge of Early Cretaceous forms following Mannion and de Souza Carvalho (2026).

(Wait a second... Mannion et al. 2019, Mannion and de Souza Carvalho 2026, Mannion as third author on Beeston et al. 2024... Philip Mannion, stop taking my titanosaurs!)

In this case, the affected species were Hamititan xinjiangensis, Ninjatitan zapatai, and Volgatitan simbirskiensis. Although from different continents and formations, all three share one key characteristic: Supposed Early Titanosaur. SET is almost a curse. As soon as someone starts thinking a particular sauropod represents an Early Titanosaur, it is liable to transform, as if by perverse magic, into something else, and I don't recall that any have actually gotten back to being classified as titanosaurs. The main culprit seems to be that we just don't really have a good grasp on what somphospondyls were up to in their early years. (Well, that and the inevitability that the closer you get to the base of any lineage, the more generalized the taxa. And, perhaps, sometimes people might get too enthusiastic hoping for an Early Titanosaur and read a bit more into specimens than is warranted.) Somewhere in there is the lineage that led to titanosaurs, but until they established their monopoly, it's difficult to distinguish that thread from various also-rans, plus other sauropod groups that may be confused with them when you only have a couple of bones.

Backing up for a moment, Mannion and de Souza Carvalho (2026) is not primarily about reclassifying three disparate Early Cretaceous titanosaur-like sauropods. It's actually a redescription of Triunfosaurus leonardii, another victim of SET. In a minor upset for how these descriptions usually go, the type material doesn't turn out to be chimeric (the "middle-posterior caudals" are more likely anterior, but that's about as close as it gets to major anatomical reinterpretation). This then turned into an opportunity to look at the relationships of five SETs: T. leonardii, the three mentioned above, and Tengrisaurus starkovi. Running equal weighting (EQW) and extended implied weighting (EIW) against their data, they found the following placements:

• Hamititan was a turiasaurian under EQW and deeply nested in Titanosauria as a saltasauroid under EIW, which is a good trick. The authors in passing noted issues with its diagnosis and suggested it is not diagnostic at the genus level. For our purposes, I took the lowest common denominator and reassigned it to Eusauropoda.
• Ninjatitan was a diplodocid under EQW and a non-titanosaurian somphospondyl under EIW, hanging out with Chubutisaurus insignis. It isn't entirely comfortable in either position, and diplodocoids are known from the same formation, so the scrappy type could be chimeric and include both (Mannion and de Souza Carvalho 2026). For our purposes, I reassigned it to Neosauropoda.
• Tengrisaurus, boringly, was a clean titanosaur either way, although of course its exact placement in Titanosauria varied. No change was needed, and at the moment it is our oldest named titanosaur by default. Congratulations.
• Triunfosaurus was a non-titanosaurian somphospondyl under EQW and a basal titanosaur under EIW. Essentially it was either just inside or just outside the velvet rope, so hopefully that means there's a pretty good handle on it. No change was needed, as I already had it at Somphospondyli.
• Finally, Volgatitan was quite consistent... consistently a mamenchisaurid, which the authors found somewhat puzzling and not supported by the most robust of characters. A type specimen consisting of seven partial caudals also did not inspire great confidence in the results. Nevertheless, I moved it to Eusauropoda (I'm not using Mamenchisauridae until someone determines what Mamenchisaurus is and isn't).

Of these five, the two with the best cases to be recognized as true Early Titanosaurs are Tengrisaurus, which always ended up within it, and Triunfosaurus, on the doorstep. Although it's tempting to take one and plant a flag for the origin of the group, the situation is too messy for anything that neat, as noted by Mannion and de Souza Carvalho (2026). There's almost no record of somphospondyls in the Late Jurassic and earliest Cretaceous, when by definition they must have been around (because their sister group Brachiosauridae was around), and when we do start seeing them, they're all over the place (Mannion and de Souza Carvalho 2026).

References

Beeston, S. L., S. F. Poropat, P. D. Mannion, A. H. Pentland, M. J. Enchelmaier, T. Sloan, and D. A. Elliott. 2024. Reappraisal of sauropod dinosaur diversity in the Upper Cretaceous Winton Formation of Queensland, Australia, through 3D digitisation and description of new specimens. PeerJ 12:e17180. doi: 10.7717/peerj.17180.

Mannion, P. D., and I. de Souza Carvalho. 2026. Re-evaluation of the Early Cretaceous titanosauriform sauropod dinosaur Triunfosaurus leonardii from the Triunfo Basin, Brazil: implications for the initial radiations of Somphospondyli and Titanosauria. Zoological Journal of the Linnean Society 207(1): zlag073. doi: 10.1093/zoolinnean/zlag073.

Mannion, P. D., P. Upchurch, X. Jin, and W. Zheng. 2019. New information on the Cretaceous sauropods of Zhejiang Province, China: impact on Laurasian titanosauriform phylogeny and biogeography. Royal Society Open Science 6(8):191057. doi: 10.1098/rsos.191057.

Your Friends The Titanosaurs: Phosphatotitan khouribgaensis

The latest friendly titanosaur to come along hails from Morocco, making it the first named Moroccan titanosaur but not the first record. Other occurrences are mentioned here. For some reason it seems like the new names are always specimens that weren't included. Still lots of titanosaurs out there!

Your Friends The Titanosaurs: Yeneen houssayi

What do you get the formation that has five established titanosaur species and a couple of ne'er-do-wells? A sixth titanosaur, of course!

All joking aside, it's misleading to think of "Titanosauria" as a relatively small-scale group like Diplodocidae or Brachiosauridae when it's really a massive, sprawling complex including multiple distinct lineages that essentially monopolized all things sauropod in the Late Cretaceous. We talk of the Morrison Formation having diplodocids and dicraeosaurids and camarasaurids and brachiosaurids and whatever else, and that may sound more impressive than the Bajo de la Carpa Formation having six different titanosaurs. "What? You need all those titanosaurs?" "All those titanosaurs" are functionally replacing each of those smaller clades of the Morrison, as well as apparently just about everything else large and herbivorous. It's just the relationships and smaller divisions are still fuzzy. Eventually, we'll have a better grasp. But enough philosophy! Let's bring on today's guest, Yeneen houssayi. (And thank you to Alberta Claw and Stephen Poropat for supplying me with the paper!)

Silvisaurus condrayi

You wait long enough, and history starts to pile up, like falling snow (only history doesn't melt away and has a way of churning back to the surface). In paleontology, we've just passed two centuries with Megalosaurus (1824) and Iguanodon (1825). I was thinking about the topic of this post and how it was a relatively recent name, even though it felt old, but then realized that 1960 is not quite as recent as it was when I first read about Silvisaurus in the mid-1980s. I'm not tracking stats to any great degree, but it's probably safe to say there aren't a lot of people reading this who were mid-career when the scientific description of Silvisaurus condrayi was published.

A Visual Paleontological Inventory of Utah’s National Park Service Areas

Allow me to indulge in a bit of puffery and congratulations...

Let's go back a couple of years ago. We in the NPS Paleontology Program knew that the new edition of the Utah Geological Association's "Geology of Utah's Parks and Monuments" was not going to have an update of the overall park paleontology chapter. (Which is fair enough, since it was 35 pages in the previous update and was not getting shorter. The new volume is still well worth seeing, though, especially if you haven't seen the earlier editions.) We also were working with Tut Tran, then putting the finishing touches on the paleontological inventory report for Bryce Canyon National Park. These touches included some clever biostratigraphic figures of a kind we'd never used before. Thus was an idea born: Tut would prepare a standalone article featuring similar figures for the rest of Utah, with contributions from various luminaries in NPS and Utah paleontology. This article, "A Visual Paleontological Inventory of Utah’s National Park Service Areas", is now available for your edification and reading pleasure. Congrats, everyone!

Utah has 13 National Park Service units: five parks (Arches, Bryce Canyon, Canyonlands, Capitol Reef, and Zion), six monuments (Cedar Breaks, Dinosaur, Hovenweep, Natural Bridges, Rainbow Bridge, and Timpanogos Cave), one national recreation area (Glen Canyon), and one national historical park (Golden Spike). (There are a few other units in the state designated as "National", such as Grand Staircase-Escalante National Monument and Flaming Gorge National Recreation Area, but they are under different agencies.) This is omitting a few NPS trails (California, Mormon Pioneer, Old Spanish, and Pony Express) and the Virgin Wild and Scenic River, which are complicated to deal with because they don't have formal boundaries the same way the other types of units do; one day I'd like to go over rivers and trails thoroughly, but that's for another day. Anyway, the 13 units give Utah one of the best state-wide paleontological records in the NPS, up there with Alaska and California. Each one of them has something, although certainly some have more than others. The five national parks, Dinosaur NM, and Glen Canyon NRA are the most abundantly supplied and feature the longest records.

Figure 2, comparing the stratigraphic records of Utah's NPS units. Click to embiggen. CC BY 3.0 US.

These seven units are fairly similar stratigraphically and in fossil content, with the exceptions of Bryce Canyon (getting started when most of the others are tapering off) and to a certain extent Dinosaur (longer record and some different formations due to distance from the other units). The classic assortment of rocks generally includes the Permian, Triassic (Moenkopi and Chinle), Jurassic (Glen Canyon Group, San Rafael Group, and Morrison Formation), and part of the Cretaceous (Cedar Mountain Formation and Naturita, the old Dakota Sandstone). Arches, Canyonlands, Capitol Reef, and Glen Canyon in particular are geological and paleontological siblings. There are some older and some younger formations, but generally the sweet spot is between about 300 and 100 million years ago.

You might think, based on Dinosaur's reputation, that the Morrison Formation is the big producer, but as it turns out that's not the case. The Lower and Middle Jurassic rocks that make up so much of the scenic vistas, although not big bone producers, are perhaps the most iconic fossil producers with their fossil tracks. (Which is fitting for a park, because just like you can't put a vista in a box and take it somewhere else, fossil tracks are best appreciated where they are found.) The Chinle and Moenkopi are also good but a bit overlooked (Utah's Chinle having the excuse of being in the shadow of Arizona and New Mexico). Another interval that is very productive is the late Quaternary: several units have cave/rock shelter assemblages, usually thanks to packrats, with the assistance of other animals. Glen Canyon in particular is noted for dung caves, including Bechan Cave ("big feces" in Navajo) and its supply of mammoth dung. The Cretaceous is coming into its own with work at Bryce Canyon, Dinosaur, and Glen Canyon; in fact, work on the Cretaceous made our article outdated almost the day it was published, thanks to Pahasapasaurus gillettei from the Tropic Shale of Glen Canyon (Schmeisser McKean 2025). We were able to get October's Athenar bermani in there in the proof stage, but the plesiosaur managed to wait just long enough. (Darn it.)

This article is not a rewrite of the NPS paleontology chapters in the old UGA volumes. It sets out to do different things and is much more visual in focus, rather than textual. (It even has its own nifty cover image, done by artist Benji Paysnoe in the spirit of the great "Vertebrate Paleontology of Utah" volume.) The main things you will find in this that you won't find in the older chapters are Tut's outstanding diagrams and a grand 62-page appendix listing fossil taxa from each park unit by formation, with citations. Between the nine authors, I think we were able to put together a pretty darn comprehensive appendix, although doubtless we missed something. (If you spot something, let us know, so it can be included if we get the opportunity to do an update.) Me, of course, I'm hoping for more Paleozoic invertebrates, but I'm not turning up my nose at anything!

Figure 39, a sample diagram (Rainbow Bridge NM). You should go to the article to see what's been found at the big parks! CC BY 3.0 US.

We're all excited for this to be out, and we hope you find it useful as well, as a unique look at the paleontological riches of Utah's NPS units.

References

Schmeisser McKean, R. L. 2025. A new species of Pahasapasaurus (Plesiosauria: Polycotylidae) from the Upper Cretaceous Tropic Shale (lower Turonian) of southern Utah, U.S.A. Cretaceous Research 106269. doi: https://doi.org/10.1016/j.cretres.2025.106269.

Tran, T., A. R. C. Milner, J. S. Tweet, D. D. DeBlieux, R. Hunt-Foster, A. B. Shaffer, J. I. Kirkland, E. Warner-Cowgill, and V. L. Santucci. 2025. A visual paleontological inventory of Utah’s National Park Service areas. Geology of the Intermountain West 12: 221–292. doi: https://doi.org/10.31711/giw.v12.pp221-292.

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.

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.

Odds and Ends

Several items worth a brief comment...

Minnesota state fossil

By Minnesota law, Castoroides ohioensis, the "giant beaver", became Minnesota's state fossil on July 1, 2025. C. ohioensis is a rare case of a write-in winning (the original slate of candidates did not include it). Call me a lot of things (crazy, no fun, pessimistic about human nature), but I have a hard time believing the giant beaver won based on its merits as a fossil found in Minnesota, as opposed to a bunch of people on the Internet thinking it would be funny for Minnesota's state fossil to be a giant beaver. Which, I suppose, is a reasonable response to the idea of state symbols in general and state fossils in particular.

Enigmacursor

Speaking of pessimism, no sooner are all previous names for Morrison Formation "hypsils" declared dubious than a paper by the same authors comes out naming... a new Morrison Formation "hypsil". (Not the first time this kind of thing has taken place, but usually the declaration of invalidity and the new name come in the same paper.) Anyway, the new one is Enigmacursor mollyborthwickae, based on a partial skeleton from Colorado featuring vertebrae, ribs, and most of the girdles and limbs. It's not one of the more famous (well, "famous", but bear with me) unnamed Morrison specimens like BYU ESM 163R or "Barbara" but instead was recovered a few years ago. (Some days it feels like famous unnamed specimens *never* get described, but I digress.) Given the matter of chimeric specimens discussed in the Nanosaurus paper, a quarry map would have been a nice inclusion. E. mollyborthwickae looks and phylogenetically acts about the way you'd expect out of a Morrison "hypsil". I wouldn't expect that it actually *is* the closest relative to Yandusaurus hongheensis among all dinosaurs known to date (for one thing, that's putting a lot of faith in Yandusaurus, one of those dinosaurs that seems more complete and better known than it is), but that's about where Morrison "hypsils" always turn up.

Tyrannosaurus

Meanwhile, on the reincarnation of the Dinosaur Mailing List, the Dinosaur Mailing Group, the hot topic has been Tyrannosaurus and nanotyrants. Some things never change, after all. It's not a spontaneous irruption, but driven by Gregory Paul's new review of latest Cretaceous western North American tyrannosaurs. This follows on the paper a couple of years ago proposing to split T. rex into three species. Paul further revises Tyrannosaurus in this paper, supporting not only the removal of Nanotyrannus lancensis, but also Stygivenator molnari. (If you remember using the word "aublysodont" seriously, you know what's up, and there's an excellent chance you're also at least 40.) These two species are interpreted as having crossed over from Appalachia (the eastern half of North America) with the dwindling of the Western Interior Seaway, which is a fascinating idea worth further consideration.

Will it settle anything? I don't expect it to. At this point it feels like everyone is well beyond being burned out on the topic and is firmly set in their ways. It doesn't help that Nanotyrannus, along with spinosaurs and exaggerated dinosaur sizes, is one of the most obnoxious long-running issues among dinosaur enthusiasts, providing further incentive to stay the heck away. It's a pity, though, because there's something something weirdly Alioramus-y going on with some of these specimens, and all we ever do is circle around the same couple of points we always have.

Probably 25 years ago or more I posted something on the DML about a taxonomic discussion, and another member suggested we'd be better off not using the names at all and just using specimen numbers. I thought it was crazy at the time since they're a lot harder to keep track of, but with time I'm definitely coming around to the idea.

Lithodendron

The second issue of Lithodendron, Petrified Forest National Park's journal, has just come out. Contributions to this issue include a report of a large silesaurid (and coelophysoid) from the park, and the printing of a previously unpublished stratigraphic study of the park from 1940 (always good to see formerly overlooked research get published!).

Cenozoic Life and Mesozoic Life in the National Parks coloring books

Finally, some uncomplicated fun: We've recently produced coloring books of Cenozoic and Mesozoic life in the National Parks to go with the Prehistoric Life in the National Parks coloring book from a few years back. They feature a mix of artwork from the original coloring book plus newer pages. The links above will take you to the data store pages for the two books, which can be downloaded freely as pdfs. Parks with notable Cenozoic or Mesozoic fossils may also have physical copies available.

References

Maidment, S. C. R., and P. M. Barrett. 2025. Enigmacursor mollyborthwickae, a neornithischian dinosaur from the Upper Jurassic Morrison Formation of the western USA. Royal Society Open Science 12(6):242195. doi: https://doi.org/10.1098/rsos.242195

Paul, G. S. 2025. A presentation of the current data on the exceptionally diverse non-tyrannosaurid eutyrannosaur and tyrannosaurini genera and species of western North America during the End Cretaceous North American Interchange. Mesozoic 2(2): 85–138. https://doi.org/10.11646/mesozoic.2.2.1

Feeding Diamantinasaurus

It's no secret that we like titanosaurs here at Equatorial Minnesota, and another favorite topic is potential gut contents in herbivorous dinosaurs (albeit we don't see a lot of papers on it). When Poropat et al. (2025)'s paper on the potential gut contents of a specimen of Diamantinasaurus matildae came out a couple of weeks ago, it was an obvious paper to cover here. True, diamantinasaurus may not be titanosaurs by phylogeny, but they're close, and they're still titanosaurs in our hearts.

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:

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

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.

Prosauropod rehab

I once wrote that "When you get interested in something, what's already there when you arrive will seem like it has always been there, and everything that comes along later will always seem a little new to you, even if it has been decades." Taxonomic fashion is one of those things. When I got into dinosaurs in the mid-1980s, prosauropods had shrunk to something like a half-dozen well-regarded genera plus some dross and a few names that were too new for someone to have gotten around to sinking. One of the survivors was always Ammosaurus, which somehow parlayed a few pelvic differences from Anchisaurus into family-level separation (Ammosaurus the plateosaurid, Anchisaurus the anchisaurid). Meanwhile, all of Africa's prosauropod diversity was being crammed, with varying degrees of success, into Euskelosaurus, Massospondylus, these things called "roccosaurids", and Aristosaurus. (Aristosaurus? You had to be there.) Since I had no personal memory of the work that had gone on in years before, and at five years old wasn't really pouring through the primary literature, it seemed like things had always been that way. This is not the case, though. The vast majority of this synonymization had taken place in the previous 10–15 years and was the work of just a few authors. What had come before that?

Well, obviously, what had come before that were the decades of describing and naming scads of prosauropods; otherwise, there wouldn't have been anything to synonymize. It seems like people loved to name them and then forget about them. The history of their research is littered with misconceptions, some of which seem blindingly obvious in hindsight (big predatory prosauropods? You sure you're not just looking at shed crowns from carnivorous animals?). It's a matter of lack of respect and interest: If dinosaurs were a sideshow to the evolution of important things (i.e., mammals), prosauropods were a sideshow to the sideshow, a couple of card tables featuring a guy with a big unibrow and someone doing "pull my finger" jokes.

Skip ahead a few decades. Some of my readers will have never heard of Aristosaurus (well, okay, nobody living has heard of Aristosaurus except me and maybe 10 other people who have been sworn to secrecy, and now I've lost my membership in the group for a cheap gag) and know only of Euskelosaurus as this thing that nobody talks about except to badmouth in the "Background" section of papers. You wouldn't remember the heady days of the '00s, when that genus collapsed under the weight of its synonyms. Instead, it will have always been a nomen dubium to you, and if it somehow returned (stranger things have happened), it wouldn't be a resumption of your interrupted Euskelosaurus service but something new. (Why, yes, I do have a sense I'm getting older. The only thing that saved me from being older than all MLB players this year was four games and 3 2/3rds innings from Rich Hill.)

Anyway, I've long had a soft spot for prosauropods. They're never been supremely popular and had the poor marketing insight to go extinct before they could be menaced by particularly charismatic theropods, but they have a subtle charm, like small bipedal ornithischians. Over the past year or so, there's been a series of papers providing redescriptions and historical analyses of some of the most venerable genera and species of prosauropods, including comments on some of those 1970s–1980s synonymizations. They include Barrett and Chapelle (2024) on Massospondylus, Barrett and Choiniere (2024) on Melanorosaurus, and Regalado Fernández et al. (2023) and Schaeffer (2024) on Plateosaurus.

Massospondylus

Another instance of perception not matching up with chronology: one of the things that comes out of Barrett and Chapelle (2024) was that before the 1970s, Massospondylus was kind of a dog of a taxon. It achieved its present exalted status mostly by getting there first and being less of a dog than the other choices. If Richard Owen had decided to lead with Leptospondylus or Pachyspondylus in 1854 instead of Massospondylus, it wouldn't have had that first point in its favor, and then where would we be? When a name was needed to absorb the mid-sized prosauropods of the Early Jurassic of southern Africa, M. carinatus was there waiting. Some of the new material was good enough to support a name, and our conception of Massospondylus carinatus drifted from the varied bones named by Owen to that material, which eventually supplied a neotype (a type or name-bearing specimen selected after a species was named, to replace a type that was lost or not specified). The original material was no longer available to query, having been destroyed in World War II, but casts and line drawings of some of it remain, and Barrett and Chapelle (2024) provided redescriptions of as much as they could. In the end, it's just as well that the species is now represented by a neotype, because that original material is not diagnostic beyond the level of Massospondylidae at best. The drift of the conception of Massospondylus, plus the uncritical assignment of a lot of material since the 1970s, leaves the possibility of surprises once "Massospondylus" specimens are thoroughly examined. This also applies to Melanorosaurus and Plateosaurus. (Granted, I'm not convinced that every new genus and species will stand the test of time, but that's for another time, when the pendulum eventually swings back to consolidation.)

Massospondylus as a flowchart. Figure 4 of Barrett and Chapelle (2024). CC BY 4.0.

Melanorosaurus

Proposed synonymizations don't always pan out, of course (one reason not to go overboard committing to the conclusions of New Paper Of The Week). The proposed sinking of Lufengosaurus and Yunnanosaurus into Massospondylus at the height of prosauropod consolidation did not attract much support, and the proposed sinking of Melanorosaurus into Euskelosaurus fared only marginally better. Although it escaped that fate, Melanorosaurus has never seemed to get much respect. It's almost a reflex for authors to mention its questionable type material, as if apologizing for trotting it out. Barrett and Choiniere (2024) went back to the original syntype series (a group of specimens used to bear a name) to see what could be salvaged.

M. readi, like many a species, was based on your standard pile o' bones of unclear association. Barrett and Choiniere (2024) regarded a subset, including several partial or complete vertebrae, an ulna, a radius, an ilium, a partial pubis, two tibiae, a fibula, and parts of four metatarsals, as representing one skeleton that they designated a lectotype (a name-bearing specimen selected from a syntype series). Furthermore, they were able to find several diagnostic features. It's not the prettiest type, but it *is* useable. The authors compared the lectotype to several other specimens frequently used as Melanorosaurus exemplars in the literature. Unfortunately, this part doesn't go quite so well for M. readi; NMQR 3314, one of the more important specimens (including a skull), is excluded on both anatomic and stratigraphic grounds. Another specimen, NMQR 1551, is considered consistent with M. readi but an assignment is not confirmed. (I personally hope it is, because I don't want an excuse for someone to try to bring back "Roccosaurus" as a name.) The upshot is M. readi is valid but not particularly helpful at the moment, pending reclamation of more complete material.

Plateosaurus

If Massospondylus is what you get when specimen assignment goes to the last species standing, Plateosaurus is what happens when people care too much. For sheer mind-numbing taxonomic complexity in the world of dinosaurs, it's hard to beat the adventures of Upper Triassic European prosauropods. An extensive historical review can be found in Regalado Fernández et al. (2023), along with detailed reports on many of the significant specimens involved in the story. One of the things I find useful is rather than synonymize the many lesser lights with a species of Plateosaurus, the authors treat them as dubious species. Why is this useful? Keeping them separate helps to keep the concept of the host species from drifting. It's not as if there's some prize for having the tidiest faunal list, after all; specimens should only be assigned to the level of confidence.

Stratigraphic distribution of German Plateosaurus and friends. I could quote every figure in this article, but then I might as well reproduce the whole thing. Figure 2 in Regalado Fernández et al. (2023) CC BY 4.0.

Coming at Plateosaurus from a different angle, Schaeffer (2024) redescribed the holotype (singular name-bearing specimen) of P. trossingensis, which became the type species of Plateosaurus a few years back (another long story). This gets right at the heart of the taxonomic drift: you have to establish your basis of comparison before you can compare anything to it. Continuing with this, Schaeffer ran a phylogenetic analysis of sauropodomorphs with Plateosaurus trossingensis based just on the holotype. Fortunately, the species behaved predictably in terms of general location and neighbors.

References

Barrett, P. M., and K. E. J. Chapelle. 2024. A brief history of Massospondylus: its discovery, historical taxonomy and redescription of the original syntype series. Palaeontologia africana 58: 97–131.

Barrett, P. M., and J. N. Choiniere. 2024. Melanorosaurus readi Haughton, 1924 (Dinosauria, Sauropodomorpha) from the Late Triassic of South Africa: osteology and designation of a lectotype. Journal of Vertebrate Paleontology 44(1): e2337802. doi: https://doi.org/10.1080/02724634.2024.2337802

Regalado Fernández, O. R., H. Stöhr, B. Kästle, and I. Werneburg. 2023. Diversity and taxonomy of the Late Triassic sauropodomorphs (Saurischia, Sauropodomorpha) stored in the Palaeontological Collection of Tübingen, Germany, historically referred to Plateosaurus. European Journal of Taxonomy 913(1): 1–88. doi: https://doi.org/10.5852/ejt.2023.913.2375

Schaeffer, J. 2024. Osteological redescription of the holotype of Plateosaurus trossingensis (Dinosauria: Sauropodomorpha) from the Upper Triassic of SW Germany and its phylogenetic implications. Journal of Systematic Palaeontology 22(1): 2335387. doi: https://doi.org/10.1080/14772019.2024.2335387

Secrets of "Secrets Of The Dinosaur Mummy", or: How I Got An IMDb Entry

A few days back I did something I hadn't done since 2008: I watched "Secrets of the Dinosaur Mummy". This was mostly because I had a friend over and wanted to show her what the Leonardo thing was all about, along with my minor claim to small-screen fame. Obviously going that road brought out the memories, so I thought maybe it was time to have a look back. Getting the "Truth in Advertising" out of the way up-front: I don't actually have a lot of secrets about "Secrets of the Dinosaur Mummy", but I do know a title when I see one!

It turned out to be unexpectedly difficult to get a good photo of the cover, being moderately glossy and dark, but you get the idea. One of these two blurbs is good for a chuckle, given the prominence of the speaker in the documentary.

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.)

Your Friends The Titanosaurs: Qunkasaura pintiquiniestra

2024 has been a great year for new titanosaurs, as we are now on the fifth to be announced and we're still more than three months from the end of the year. For a change of pace, this time we're heading to Europe. Qunkasaura pintiquiniestra, the first new European titanosaur in more than two and a half years, hails from the Lo Hueco site in Spain.