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

Roundup on Thunderstorm Ridge: keeping up with Petrified Forest NP

Last week's publication of the stem-caecilian Funcusvermis reminded me that I really ought to show off Petrified Forest National Park (PEFO) more often. Since the last spotlight, on the "biloph" trilophosaur Trilophosaurus phasmalophus in spring 2020, four more species of Triassic vertebrates have been described from fossils found in the park, to go along with a bushel of reports on anatomy, identifications of rare forms, vertebrate trace fossils, stratigraphy and geochronology, and other topics, to say nothing of conference abstracts and papers that mention PEFO fossils in wider contexts. (SVP conferences are usually good for a handful of PEFO topics.) Because we're talking the Late Triassic, the taxonomic diversity is wide. There's a little bit of almost everything.*

*Interestingly enough, that includes Paleozoic marine invertebrates: reworked fossiliferous cobbles of the Permian Kaibab Formation have been found in the park's Chinle Formation outcrops, particularly the Sonsela Member. There are also limited Neogene deposits with Hemphillian vertebrates.

Classically, as with most places that have produced vertebrate fossils for more than a century, big singular fossils were long the focus (e.g., skulls of phytosaurs). Although there is still interest in those kinds of fossils, increasingly study has focused on bonebeds and microvertebrates, with much more care given to stratigraphic placement. It turns out that PEFO holds a whole weird and wonderful landscape of everything that gave it a go in the Late Triassic, before a couple of groups of archosaurs took over land management for the rest of the Mesozoic. (And if you don't like vertebrates, the plants are just about as wild in their own way, and there are freshwater and terrestrial invertebrates as well.) It practically begs for a book like those on Florissant, Fossil Lake, the Morrison, and the White River Badlands.

Here's a strat column to help keep the geologic units straight, borrowed from the park website.

With all of that in mind, here are a few quick hits from the past few years of research at PEFO:

Trilophosaurus and Ophthalmothule

For this post, we highlight two extinct reptiles that have been the subjects of publications in the past few days. Other than that, they don't have much in common. One is a short-necked terrestrial herbivore less than three meters long that lived during the Late Triassic in what is now Arizona, the other is a long-necked marine carnivore between five and six meters long that lived at about the Jurassic–Cretaceous boundary at what is now an Arctic island (not quite so arctic at the time).

Tiny frogs of the Chinle

I am embarrassed to realize that after five full years of doing this, with a header mentioning "National Park Service paleontology" and "the Mesozoic", I had not done anything with the Chinle Formation or Petrified Forest National Park. This week offers a fine opportunity to correct this oversight, with the publication of the first frog fossils from the Chinle Formation.

The Chinle Formation is a terrestrial unit, with its colorful rocks deposited in various floodplain, river, lake, and other settings during the Late Triassic. The mosaic of settings led to a variety of rock types, from conglomerates to mudstones, with a healthy supply of volcanic ash from eruption centers to the west. Because we're talking about the Late Triassic, before the end-Triassic extinctions gave dinosaurs the opportunity to fill most of the empty terrestrial niches, the Chinle is full of fossils from all sorts of unusual and obscure animals. (And also petrified wood and freshwater mussels. Lots and lots of petrified wood and mussels!) It and its correlatives are usually good for at least one surprise every few years. Lurking among all of the phytosaurs and aetosaurs and so forth were representatives of lineages that would blossom later. Some of them we know from bones (dinosaurs, early croc relatives, pterosaurs, etc.), others can be suspected based on time and place but haven't yet been found. With this week's announcement, frogs move from the potential to the confirmed (Stocker et al. 2019).

The Chinle Formation is divisible into a number of members, depending on where you are. In ascending order, the units in the Petrified Forest NP area are the Mesa Redondo, Blue Mesa, Sonsela, Petrified Forest, and Owl Rock members. For the frogs, we're dealing with the Blue Mesa and Sonsela members, representing approximately 223 to 213 million years ago. (Following the stratigraphy of the Chinle Formation requires a certain amount of effort and dedication. Not only are different members found in different places, but usage has varied over time.) The three frog-producing localities are spread from the park to the famous Placerias Quarry near St. Johns, Arizona (Stocker et al. 2019).

An outcrop of the Sonsela Member, from the park website (NPS/Andrew V. Kearns).

Frogs, being small and delicate, are not exactly heavily represented in the fossil record. The frog lineage, Salientia, is known back to the Early Triassic, but if you were doing a Compact Thescelosaurus-like project on Mesozoic salientians you'd be finished pretty quickly. Salientia includes early stem-frogs plus the crown group Anura, which is the group consisting of all living frogs, their most recent common ancestor, and everything else that falls within that group. There are to date two Early Triassic stem-frogs, the well-known Triadobatrachus of Madagascar and the somewhat less famous Czatkobatrachus of Poland, with the next named salientian being a respectable frog's jump all the way into the Early Jurassic of Arizona, Prosalirus of the Kayenta Formation. The Kayenta has historically proven stubborn about this whole "absolute dating" thing, but an age in the first half of the Early Jurassic is the consensus, so that's a gap of something approaching 60 million years (approximately 250 to 190 million years). The unnamed Chinle salientian practically splits the difference (Stocker et al. 2019).

The Chinle salientian is known from five tiny fossils. Fortunately, four of them are ilia, which are very distinctive bones in frogs: there is a cup-like socket for the femur and a long thin blade directed anteriorly, lengthened by cartilage, part of the mechanism that gives frogs their spring. In the case of the Chinle form, they are also well into the microvert range: approximately 6.2 mm long, or about a quarter of an inch, the kind of stuff you find when you run sediment through screens as opposed to spotting while hiking around. The whole animal would have been less than about 25 mm long, or about an inch, in the realm of modern miniature frogs (Stocker et al. 2019). So, if you were thinking that ur-frogs might have been prehistoric giants, well... not so much in the Chinle. There *were* enormous amphibians in the Chinle, specifically the metoposaur Koskinonodon and its equally enormous taxonomic history, but it isn't closely related to anything living and it didn't look much like a frog.

The form of the hip joint and shaft suggest that the Chinle form was well on the way to modern frog jumping mechanics (Stocker et al. 2019). It may have been a true anuran, but only time and more fossils will tell. The presence of a stem-frog or true anuran in the Chinle also has some implications for frog distribution and paleoecology. The two Early Triassic stem-frogs lived outside of the tropics, whereas the Chinle form was more or less at the equator in western Pangea, showing that the frog lineage had spread across the supercontinent within the Triassic. Also of interest is the persistence of salientians from the Chinle into the Kayenta; over the length of the Chinle, the local climate became more and more arid (Stocker et al. 2019).

A Triassic frog clings to the snout of a phytosaur, used with permission by Andrey Atuchin (supplied by Adam Marsh/PEFO).

References

Stocker, M. R., S. J. Nesbitt, B. T. Kligman, D. J. Paluh, A. D. Marsh, D. C. Blackburn, and W. G. Parker. 2019. The earliest equatorial record of frogs from the Late Triassic of Arizona. Biology Letters 15:20180922. doi:10.1098/rsbl.2018.0922.