Fossil Ursids of the National Park Service

Here we are, a little later than usual for the annual "Fossil [Group] of the National Park Service" but present nonetheless. I decided to get in another group of carnivorans, this time the bears (Ursidae). If you've been here for the cats and dogs, you can probably guess the basic shape of things: a few records earlier in the Cenozoic, then a big slug in the Pleistocene into the Holocene, with many of the records representing living species. That is indeed how it goes with the bears as well, with a couple of quirks: the bear record goes back as far as the dog record, into the Chadronian (Late Eocene), but is never as diverse as the records for either cats or dogs. Essentially you get a couple of genera or species in a formation, and that's about it. Bears, it seems, have never felt the need to be profuse about the business of being bears. It's not quite "one-bear-fits-all", but bears favor generalism, and there's only room for so many species of generalists in one place and time.

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