Paleontology of Scotts Bluff National Monument

Those of us old enough to have attended elementary school circa 1985–1990 may remember the experience of successfully (or less-than-successfully) traversing The Oregon Trail. Although the game certainly included a great deal of content and detail, you can play as long as you like but you'll never find a trace of a fossil in it. The people who actually used the real Oregon Trail and its counterparts did find fossils, though. One such intersection of paleontology and human history is Scotts Bluff National Monument (SCBL), which you can read about in our freshly issued paleontological resource inventory (Shaffer et al. 2026).

A former exhibit at the monument's visitor center highlighted examples of journal records. Figure 2 in Shaffer et al. (2026).

SCBL is part of a small cluster of National Park Service units that document the middle Cenozoic of the northern Great Plains. The most famous of these is Badlands National Park and its White River Group, but of course there is also Agate Fossil Beds National Monument and the younger Arikaree Group. Niobrara National Scenic River we saw last year. Wind Cave National Park also has some White River Group outcrops, and Fort Laramie (another place in The Oregon Trail) of today's Fort Laramie National Historic Site sits among Arikaree Group strata and was used by O.C. Marsh as a base of operations. Another Trail landmark, Chimney Rock, is the focus of NPS-affiliate Chimney Rock National Historic Site as well as the source of type specimens for the bird Phasianus (now Archaeophasianus) mioceanus Shufeldt 1915 and the rodent Eumys brachyodus Wood 1937. SCBL fits quite neatly among this regional crowd, complementing some of them and partially filling the temporal and stratigraphic gap between the Early Oligocene of Badlands and the Early Miocene of Agate Fossil Beds.

Click to expand for the annotations. 120 years can make a difference! Figure 5 in Shaffer et al. (2026).

The new report includes a new stratigraphic column for the monument and a detailed discussion of the mammalian biostratigraphy. Stratigraphically the monument encompasses the Oligocene part of the White River Group (Brule Formation), the mid-Oligocene Gering Formation, and younger undivided strata of the Arikaree Group. The biostratigraphy and lithostratigraphy are not quite nailed down at the top, but there is reasonable (but not conclusive) evidence that it gets into the late Early Miocene (Hemingfordian).

And if you want the technical explanation for the previous image... Figure 7 in Shaffer et al. (2026).

What kinds of fossils have been found at the monument? The great majority with solid location information come from the Brule Formation, so if you're familiar with Badlands, Scotts Bluff won't seem terribly different. There are the inevitable turtles (observed by 19th century travelers), oreodonts, and nimravids, and a whole host of ungulates. (There are only so many ways to say "small, extinct, and deer-like". It's a bit like "hypsilophodont" for any small bipedal ornithischian.) The higher stratigraphic units have not been as profuse with vertebrate body fossils as the Brule, but they do all right with trace fossils. In fact, trace fossils are one of the monument's specialties. There are vertebrate burrows in the Brule about 0.3 meter (1 foot) across and up to 4 meters (13 feet) long. One is associated with a turtle specimen. Cross-sections of animal tracks can be seen in the Gering Formation, some of which may have been made by entelodonts. Root traces and invertebrate burrows are abundant in the undivided Arikaree Group (Shaffer et al. 2026).

A number of tracks can be seen in cross-section just above the pronounced break, and the underside of one is just peeking out a little right of center. Figure 12 in Shaffer et al. (2026).

Although the people traveling by Scotts Bluff did not have time to do much more than note fossils, the site and its geologic exposures attracted geological interest. As a result, there are substantial vintage collections from "Scotts Bluff" (regrettably little other provenance information at hand) at the American Museum of Natural History, Harvard's Museum of Comparative Zoology, the Smithsonian, and especially Yale's Peabody Museum of Natural History, which has probably the longest history. At least seven fossil taxa were named from specimens found at or in the vicinity of the bluff, although only four could still be considered in use. Despite the evident interest, a comprehensive description of the site's paleontology has not been prepared until now. Scotts Bluff National Monument can take its rightful place among the paleontological parks of the Great Plains.

References

Shaffer, A. B., E. Evanoff, E. Welsh, J. S. Tweet, and V. L. Santucci. 2026. Scotts Bluff National Monument: paleontological resource inventory (public version). Science Report NPS/SR—2026/504. National Park Service, Fort Collins, Colorado. https://doi.org/10.36967/2319364.

Shufeldt, R. W. 1915. Fossil birds in the Marsh Collection of Yale University. Transactions of the Connecticut Academy of Arts and Sciences 19: 1–110.

Wood, A. E. 1937. The mammalian fauna of the White River Oligocene. Part II. Rodentia. Transactions of the American Philosophical Society 28(2): 155–269.

Fossil Marine Mammals of the National Park Service

This year it works out that I'm a little early for the annual "Fossil [Group] of the National Park Service", and we continue our tour of mammal groups with a bit of a grab-bag. As with the marine reptiles, there is not one single group of marine mammals. Rather, several different groups became adapted to the oceans. There are the cetaceans, including whales, dolphins, and porpoises (and yes, dolphins and porpoises are small whales, but you know what I mean). There are the pinnipeds, including animals such as seals, sea lions, and walruses (and yes, there are two distinct groups of pinnipeds called seals, true seals without ears and eared seals that are closer to sea lions; it wouldn't be an Equatorial Minnesota post without mentioning at least a couple of caveats and technicalities, after all). Finally, we also have sirenians (dugongs and manatees) and desmostylians (extinct, kind of hippo-like things), two herbivorous groups that may or may not have been related.

New thematic inventories and a bit more cave paleontology

A couple of thematic inventories have just been published with the involvement of the NPS Paleontology Program. One of these is the first part of a paleobotany series, eventually to be three parts covering the Cenozoic, Mesozoic, and Paleozoic. The first part, Matel et al. (2026), covers the Cenozoic and is available for download through February 24. This is one of the projects from the National Park Service-Paleontological Society Paleontology in the Park Fellowship Program. In it, we've worked to provide information on Cenozoic paleobotany for every park unit where it's known. (It's easier to do concisely when the record is one piece of petrified wood than when the park is, say, Florissant Fossil Beds National Monument, so necessarily the scale of detail varies.) For practical reasons the focus is on macrofossils, with pollen and such as an adjunct.

The other new inventory, Santucci et al. 2025, covers NPS cave paleontology from 2002 to 2023. This is presented as an update of a previous report (Santucci et al. 2001). I'm taking the opportunity here to add a postscript because the past couple of years have been very productive. First of all, we came upon a new park record: Kalaupapa National Historical Park, on the north side of Molokaʻi, Hawaii. Although main focus here is historical, this park has a very interesting geological story too, involving the collapse of a volcano and the subsequent growth of another smaller volcano. The smaller volcano is now extinct, leaving behind Kauhakō Crater. Inside the crater people have found bird bones in a cave. One is a partial ulna of the extinct flightless ibis Apteribis glenos, the other is a coracoid of Pterodroma hypoleuca, the modern Bonin petrel, which does not live on the island today (Olson and James 1982, 1991).

Also, a few things in press or under study have progressed in the past couple of years. Avid readers of this blog will know that the "musk ox" of Muskox Cave at Carlsbad Caverns National Park is now named Speleotherium logani (White et al. 2025). The Cumberland Bone Cave monograph has also been published (Eshelman et al. 2025). Most notable, though, has been the publication of work on Mammoth Cave National Park. The park inventory (Toomey et al. 2025) was mentioned here a few months back. There has also been a good short summary of the Mississippian vertebrates (Hodnett et al. 2024a) and no fewer than five new taxa: ctenacanthiforms Troglocladodus trimblei and Glikmanius careforum (Hodnett et al. 2023); petalodonts Clavusodens mcginnisi (Hodnett et al. 2024b) and Strigilodus tollesonae (Hodnett et al. 2024c); and holocephalan Macadens olsoni (Hodnett et al. 2025).

Clavusodens mcginnisi on the prowl, among the crinoids. Illustration by Benji Paysnoe for the National Park Service.

References

Eshelman, R. E., C. J. Bell, R. W. Graham, H. A. Semken, Jr., C. B. Withnell, S. G. Scarpetta, H. F. James, S. J. Godfrey, J. I. Mead, J.-P. Hodnett, and F. V. Grady. 2025. Middle Pleistocene Cumberland Bone Cave Local Fauna, Allegany County, Maryland: a systematic revision and paleoecological interpretation of the Irvingtonian, Middle Appalachians, USA. Smithsonian Contributions to Paleobiology 108.

Hodnett, J.-P., R. Toomey, H. C. Egli, G. Ward, J. R. Wood, R. Olson, K. Tolleson, J. S. Tweet, and V. L. Santucci. 2023. New ctenacanth sharks (Chondrichthyes; Elasmobranchii; Ctenacanthiformes) from the Middle to Late Mississippian of Kentucky and Alabama. Journal of Vertebrate Paleontology 43(3): e2292599. doi: 10.1080/02724634.2023.2292599.

Hodnett, J.-P., R. Toomey, R. Olson, K. Tolleson, R. Boldon, J. Wood, J. S. Tweet, and V. L. Santucci. 2024a. Sharks in the dark: Paleontological resource inventory reveals multiple successive Mississippian Subperiod cartilaginous fish (Chondrichthyes) assemblages within Mammoth Cave National Park, Kentucky. Park Stewardship Forum 40(1): 53–67. doi: 10.5070/P540162921.

Hodnett, J.-P. M., H. C. Egli, R. Toomey, R. Olson, K. Tolleson, R. Boldon, J. S. Tweet, and V. L. Santucci. 2024b. Obruchevodid petalodonts (Chondrichthyes, Petalodontiformes, Obruchevodidae) from the Middle Mississippian (Viséan) Joppa Member of the Ste. Genevieve Formation at Mammoth Cave National Park, Kentucky, U.S.A. Journal of Paleontology 98(6): 1087–1097. doi: 10.1017/jpa.2024.40.

Hodnett, J.-P., R. Toomey, R. Olson. J. S. Tweet, and V. L. Santucci. 2024c. Janassid petalodonts (Chondrichthyes, Petalodontiformes, Janassidae) from the middle Mississippian (Viséan) Ste. Genevieve Formation, Mammoth Cave National Park, Kentucky USA. Historical Biology 36(9):1783–1792. doi: 10.1080/08912963.2023.2231955.

Hodnett, J.-P., R. Toomey, H.-D. Sues, V. Santucci, K. Tolleson, and J. Tweet. 2025. A new euchondrocephalan chondrichthyan (Chondrichthyes, Euchondrocephali) from the Middle Mississippian (Viséan) Joppa Member of the Ste. Genevieve Formation at Mammoth Cave National Park, Kentucky, USA and a reassessment of the Lower Mississippian (Tournaisian-Viséan) “Helodus” coxanus Newberry, 1897. New Mexico Museum of Natural History and Science Bulletin 100: 87–93.

Matel, T. P., I. B. Huegele, C. R. Cace, K. M. M. Bober, L. D. Boucher, V. E. McCoy, E. J. Hermsen, S. R. Manchester, C. C. Visaggi, J. S. Tweet, and V. L. Santucci. 2026. Cenozoic paleobotanical resource inventory of the National Park System. Elements of Paleontology. Cambridge: Cambridge University Press. 10.1017/9781009770477.

Olson, S. L., and H. F. James. 1982. Prodromus of the fossil avifauna of the Hawaiian Islands. Smithsonian Contributions to Zoology 365: 1–59.

Olson, S. L. and H. F. James. 1991. Descriptions of thirty-two new species of birds from the Hawaiian Islands. Part I. Non-Passeriformes. Ornithological Monographs 45:1-88.

Santucci, V. L., J. Kenworthy, and R. Kerbo. 2001. An inventory of paleontological resources associated with National Park Service caves. National Park Service Geological Resources Division Technical Report NPS/NRGRD/GRDTR-01/02.

Santucci, V. L., J.-P. Hodnett, P. Seiser, J. S. Tweet, and J. Wood. 2025. National Park Service cave paleontology: 2002-2023. Journal of Cave and Karst Studies 87(4):108–116. doi: 10.4311/2024PA0119.

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 

White, R. S., J. I. Mead, and G. S. Morgan. 2025. Logan's austral scrubox, a new ovibovine (Mammalia: Artiodactyla: Bovidae) from Muskox Cave, Eddy County, New Mexico. New Mexico Museum of Natural History and Science Bulletin 101: 473–494.

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.

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

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

Catching up with NPS proboscideans

I had occasion recently to review some of the records in the 2020 National Park Service fossil proboscidean inventory (Mead et al. 2020), so I thought it would be useful to produce an update on the roster of parks, National Natural Landmarks, and National Historic Landmarks that we included at that time.

Fossil Canids of the National Park Service

We've been taking a tour of Mammalia for the past two annual "Fossil [Group] of the National Park Service", and this year we'll make it three in a row with man's best friends, the Canidae. The dog record starts up in the Eocene with the hesperocyonines, who held court through the Oligocene but then petered out in the Miocene. Turning up in the Oligocene are the borophagines, or "bone-crushing dogs," and the canines, which include wolves, foxes, domestic dogs, and close relatives. Borophagines, as the nickname suggests, had robust jaws and teeth, which doesn't mean they should be typecast as slavering hypercarnivorous brutes (canids in general have been pretty flexible about diet over their history). They drop out of the record at about the end of the Pliocene, leaving the field clear for the canines, which had been a fairly minor component of the canid radiation until about the Late Miocene. If you're interested in paleontological nitty-gritty on these two groups, check out Wang et al. (1999) on borophagines and Tedford et al. (2009) on canines. Canids, incidentally, are a North American invention, and unlike some other groups that originated in North America (camels, horses, rhinos), they have never gone extinct on the continent.

Parks Stewardship Forum: National Park Service Paleontology

For the past year, my supervisor Vincent Santucci and I have been assisting the preparation of a group of articles on National Park Service paleontology for Parks Stewardship Forum. We've assembled seventeen articles from various contributors on a variety of topics and parks, covering aspects of inventory, monitoring, research, and curation, from semitechnical to technical (the Florissant and John Day articles are the most technical, if you're concerned about that). Our issue has now gone live, and you can read and download each of the articles here. I hope you find something you like!

The cover comes from one of my pet projects, the paleontology of George Washington Birthplace National Monument (for which I contributed an article).

Fossil Lagomorphs of the National Park Service

It's time for the annual focus on the paleontology of a particular group in National Park Service lands. This year we turn from the felines to one of their prey items, the lagomorphs (rabbits, hares, and pikas). So, why bunnies and pikas? To be honest, most of us have probably never given more than a moment's thought to the fossil record of lagomorphs, and that moment probably involved one of three thoughts: a nodding recognition that fossil rabbits et al. must exist; goofy speculation ("prehistoric saber-toothed rabbits"); or providing some ancient carnivore an appropriate lunch for a drawing or story. Well, you know me: I love topics nobody else is talking about. (I get in fewer arguments that way.) Also, I come from a household that appreciates small mammals for what they are. In return, they seem to feel comfortable hanging around. (A Tamiasciurus hudsonicus deciding your yard is part of its territory provides entertainment value all winter; the little psychos will take on anything.) For the past couple of months a young rabbit has been a frequent visitor, so this is my tip of the cap.

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:

Fossil Felids of the National Park Service

For this year's annual focus on a fossil group in National Park System units, I am going to pay my Internet cat tax and present a quick look at the fossil felids of the parks. If you're not familiar with the history of Felidae, it may come as a surprise that cats are a relatively recent innovation. They have only a few tens of millions of years under their collective belts, and didn't arrive in North America until Pseudaelurus in the early Miocene. (Note: barbourofelids and nimravids may give off saber-toothed cat vibes, but they aren't Felidae.)

It turns out that there are 24 NPS units with cat body or trace fossils. All of the records, unsurprisingly, are early Miocene in age or younger. The great majority are Quaternary (concerning the question of when to cut off the paleontological record, caves don't discriminate if you happen to be 11,000 years old rather than 12,000 years old, and neither do we): only seven of the 24 park units have pre-Q cats. These are Big Bend National Park, Death Valley NP, Hagerman Fossil Beds National Monument, John Day Fossil Beds NM, Lake Mead National Recreation Area, Mojave National Preserve, and Niobrara National Scenic River.

These maps are so much easier to make now that I have one file with all of the parks as points, and I can just turn them on and off. 1. John Day Fossil Beds National Monument; 2. Oregon Caves NM; 3. Lava Beds NM; 4. Hagerman Fossil Beds NM; 5. Yellowstone National Park; 6. Great Basin NP; 7. Death Valley NP; 8. Tule Springs Fossil Beds NM; 9. Lake Mead National Recreation Area; 10. Mojave National Preserve; 11. Joshua Tree NP; 12. Grand Canyon NP; 13. Chaco Culture National Historical Park; 14. White Sands NP; 15. Carlsbad Caverns NP; 16. Guadalupe Mountains NP; 17. Big Bend NP; 18. Amistad NRA; 19. Waco Mammoth NM; 20. Niobrara National Scenic River; 21. Ozark National Scenic Riverways; 22. Chickamauga & Chattanooga National Military Park; 23. Potomac Heritage National Scenic Trail; 24. Valley Forge NHP.

Geographically the sites are concentrated in the southwestern US; in fact, 15 of the sites are in Arizona, California, Nevada, New Mexico, or Texas. This seems to say something about cat biogeography, given these are mostly Quaternary sites and the NPS has a pretty good Quaternary record in terms of geographic spread. I wouldn't base a thesis on it or anything, though.

It's not stated on the map, but the Quaternary record is heavy on caves; a dozen of the records are from caves or rock shelters. These included significant records at Carlsbad Caverns NP, Grand Canyon NP, Guadalupe Mountains NP, Potomac Heritage NST (Cumberland Bone Cave), and Valley Forge NHP (Port Kennedy Bone Cave).

Most of the records are body fossils, but at least three have cat trace fossils: tracks at Death Valley NP and White Sands NP, and tracks and cave scratches at Chickamauga & Chattanooga NMP. One of these sites has yielded a track type specimen, Felipeda scrivneri Sarjeant et al. (2002) from Death Valley NP. There are also eight fossil felid species named from body fossils discovered within or potentially within NPS areas (all named before the units were established):

• Felis lacustris Gazin (1933) from Hagerman (now Puma lacustris)
• Machairodus? hesperus Gazin (1933) from Hagerman (now Megantereon hesperus)
• Felis augustus Leidy (1872) possibly from Niobrara (now Panthera onca [augusta], and Pleistocene instead of Miocene in age)
• Felis (Pseudaelurus) intrepidus Leidy (1858) possibly from Niobrara (now Pseudaelurus intrepidus)
• Crocuta inexpectata Cope (1895) from Valley Forge (now Miracinonyx inexpectatus) 
• Lynx calcaratus Cope (1899) from Valley Forge (now considered a synonym of Lynx rufus)
• Smilodon gracilis Cope (1880) from Valley Forge
• Uncia mercerii Cope (1895) from Valley Forge (now considered a synonym of Smilodon gracilis)

Attaining consensus on cat taxonomy and nomenclature can be like, well, herding cats. It doesn't help that it can be difficult to tell cats apart; see a record of "Panthera onca" at Carlsbad Caverns NP becoming Panthera atrox (Kottkamp et al. 2022), and "Puma concolor" fossils at Grand Canyon NP becoming Miracinonyx trumani (Hodnett et al. 2022; take the skull for a spin here). Nevertheless, the Quaternary sample can be divided among seven species or species groups. Three are extinct:

• American cheetah (Miracinonyx inexpectatus and M. trumani): found at Carlsbad, Grand Canyon, Potomac Heritage, and Valley Forge
• American lion (Panthera atrox): found at Carlsbad, Potomac Heritage, and Tule Springs
• Saber-toothed cats (Smilodon spp.): found at Potomac Heritage, Tule Springs, Valley Forge, and Waco Mammoth

Two are still around but not this far north:

• Jaguar (Panthera onca): found at Lava Beds, Oregon Caves, Ozark, Potomac Heritage, and Valley Forge (these are all pretty far north for something we associate with tropical jungles!)
  
• Jaguarundi (Herpailurus yagouaroundi): found at Valley Forge

Finally, two are still found in the United States:

• Bobcat (Lynx rufus, with allowance for Lynx sp.): Amistad, Carlsbad Caverns, Chaco Culture*, Great Basin*, Grand Canyon, Guadalupe Mountains, Joshua Tree*, Lava Beds, Tule Springs, Valley Forge, and Yellowstone* (*=Holocene only)
• Cougar/mountain lion/puma (Puma concolor): Carlsbad Caverns, Chaco Culture*, Guadalupe Mountains, and Tule Springs

The most species-rich sites are:

• Carlsbad Caverns NP (American cheetah, American lion, bobcat, cougar)
• Hagerman Fossil Beds NM (American cheetah, Homotherium sp. [a saber-toothed cat], Lynx rexroadensis, Megantereon hesperus [or cultridens; another saber-toothed cat], Puma lacustris)
• Tule Springs Fossil Beds NM (American lion, bobcat, cougar, saber-toothed cat)
• Valley Forge NHP (American cheetah, bobcat, jaguar, jaguarundi, saber-toothed cat)

Of these four, the Hagerman assemblage is Pliocene, the Valley Forge assemblage is middle Pleistocene, and the other two are late Pleistocene. In the Pleistocene, at least, a robust cat assemblage may include a big lion-type cat, a saber-toothed cat, a smaller big cat (but apparently not cougars and jaguars at the same place), and a bobcat-sized cat.

Felids are relatively uncommon compared to the other big terrestrial carnivorans. Fossil dogs and bears are more widely distributed in NPS units than cats. Furthermore, all but one NPS assemblage that has cats also has dogs, bears, or both (the exception being the Pliocene tracks of Death Valley NP). These groups, though, are for another time...

References

Cope, E. D. 1880. On the extinct cats of America. American Naturalist 14(12):833–858.

Cope, E. D. 1895. The fossil Vertebrata from the fissure at Port Kennedy. Proceedings of the Academy of Natural Sciences of Philadelphia 47:446–450.

Cope, E. D. 1899. Vertebrate remains from Port Kennedy bone deposit. Journal of the Academy of Natural Sciences of Philadelphia, 2nd series, 11(3):193–286.

Gazin, C. L. 1933. New felids from the upper Pliocene of Idaho. Journal of Mammalogy 14:251–356.

Hodnett, J. P., R. White, M. Carpenter, J. Mead, and V. L. Santucci. 2022. Miracinonyx trumani (Carnivora; Felidae) from the Rancholabrean of the Grand Canyon, Arizona and its implications on the ecology of the “American cheetah.” New Mexico Museum of Natural History Bulletin 88:157–186.

Kottkamp, S., V. L. Santucci, J. S. Tweet, R. D. Horrocks, and G. S. Morgan. 2022. Pleistocene vertebrates from Carlsbad Caverns National Park, New Mexico. New Mexico Museum of Natural History and Science Bulletin 88:267–290.

Leidy, J. 1858. Notice of remains of extinct Vertebrata, from the valley of the Niobrara River, collected during the exploring expedition of 1857, in Nebraska, under the command of Lieut. G. K. Warren, U.S. Top. Eng., by Dr. F. V. Hayden, Geologist to the expedition. Proceedings of the Academy of Natural Sciences of Philadelphia 10:20–29.

Leidy, J. 1872. Remarks on some extinct vertebrates. Proceedings of the Academy of Natural Sciences of Philadelphia 24:38–40.

Sarjeant, W. A. S., R. E. Reynolds, and M. M. Kissell-Jones. 2002. Fossil creodont and carnivore footprints from California, Nevada, and Wyoming. Pages 37–50 in R. E. Reynolds, editor. Between the Basins: Exploring the western Mojave and southern Basin and Range Province. California State University, Fullerton, California.

Send in the nautiloids: Early Ordovician fossils of the National Park Service

Previously we looked at the National Park Service records of the late Cambrian and Late Ordovician. What comes between the late Cambrian and Late Ordovician? That's right, the Early Ordovician. (The Middle Ordovician also does, but at the moment I've got Early on my mind. You know, in North America it might actually be more practical to divide the period into Early and Late, based on the lowstand that separates the Sauk Sequence from the Tippecanoe Sequence; or, maybe not. Who knows? You start to think about things like that when contemplating the divisions of the geologic time scale; where would the lines have been placed if it had been initially developed somewhere other than northwestern Europe?)

The Early Ordovician is kind of a transitional episode; in some ways, it's like a tag to the end of the Cambrian, considering it's the wind-down of the Sauk Sequence. I get the feeling that this epoch was not necessarily the most pleasant 15 or so million years in North America, at least in some areas. For example, in the Upper Midwest the Early Ordovician is represented by our old friend the Prairie du Chien Group. The PdC was certainly not bereft of life, but a whole lot of that life was stromatolite-building cyanobacteria, and a general rule of thumb is that any non-Precambrian geologic unit that features intervals of wall-to-wall stromatolites was probably not that hospitable while being deposited. Otherwise, the groups most commonly reported from Lower Ordovician rocks in NPS areas are brachiopods, nautiloids, gastropods, trilobites, graptolites, and conodonts. Apart from the nautiloids, you might think you were back in the late Cambrian. The evolutionary flowering that is evident in Middle and especially Upper Ordovician rocks was just kind of simmering: mollusks and echinoderms were chugging (although a lot of those early echinoderms didn't catch on), but corals and bryozoans were in low gear.

By my count, as many as 15 NPS units and affiliated areas have fossiliferous Lower Ordovician rocks, although the records at several of these units are not known to be particularly impressive at this time. Four of the parks are represented by the good old PdC, with fossils at Effigy Mounds NM, MNRRA, Saint Croix National Scenic Riverway, and potentially one of the units of NPS-affiliated Ice Age National Scientific Reserve. The distribution is a decent match for Early Ordovician finds in the United States as a whole (compare to the Early Ordovician records in the Paleobiology Database, for example). The major holes are New Mexico/Oklahoma/Texas, the Hudson River Valley, and Utah; none of Utah's NPS units includes a classic Ibexian sequence, but Great Basin NP next door in Nevada is Ibexian-adjacent and no slouch itself. It hosts one of the more interesting Early Ordovician fossil records in the NPS, along with Chesapeake and Ohio Canal National Historical Park, Death Valley NP, and Pictured Rocks National Lakeshore.

As usual, click to embiggen. Our Early Ordovician parks are 1) Death Valley NP; 2) Great Basin NP; 3) Kobuk Valley NP; 4) Denali NP & Preserve; 5) Yukon-Charley Rivers NPres; 6) Wind Cave NP; 7) Mississippi National River and Recreation Area; 8) Saint Croix National Scenic Riverway; 9) Picture Rocks National Lakeshore; 10) Ice Age National Scientific Reserve (affiliated area); 11) Effigy Mounds NM; 12) Ozark National Scenic River; 13) Buffalo National Scenic River; 14) Great Smoky Mountains NP; 15) Chesapeake and Ohio Canal National Historical Park.

Chesapeake and Ohio Canal NHP preserves good examples of the standard Early Ordovician assemblage in the Stonehenge Limestone and overlying Rockdale Run Formation. The Early Ordovician of both Death Valley NP and Great Basin NP is represented by rocks of the Pogonip Group, although different formations are present at the two parks. (When considering Paleozoic paleontology, if Death Valley or Yukon-Charley Rivers don't have something, it might not be present in the NPS. In this case Death Valley has the better record.) Great Basin is distinguished for examples of some of the wacky echinoderms that proliferated during the Ordovician. Pictured Rocks National Lakeshore is noted for the oldest NPS vertebrate material (I reserve the right to be cagy about the exact placement of conodonts), consisting of armor attributed to Anatolepis (Miller et al. 2006; a pteraspidomorph, or ostracoderm in more old-timey lingo). Pictured Rocks, incidentally, has an interesting unresolved stratigraphic issue: the above specimens came from the Au Train Formation and were associated with other microfossils of Early Ordovician age (Miller et al. 2006). However, a dissertation (Oetking 1952) documented Au Train macrofossils from the lakeshore area that appear to be correlative to Platteville fossils (i.e., Late Ordovician). This all suggests to me that either the identifications of Oetking's fossils are overly generous, or that the rocks identified as the Au Train Formation are more complex than currently suspected (a cryptic unconformity, etc.).

References

Miller, J. F., R. L. Ethington, and R. Rosé. 2006. Stratigraphic implications of Lower Ordovician conodonts from the Munising and Au Train Formations at Pictured Rocks National Lakeshore, Upper Peninsula of Michigan. Palaios 21:227–237.

Oetking, P. F. 1952. The relation of the Lower Paleozoic to the older rocks in the northern peninsula of Michigan. Dissertation. University of Wisconsin, Madison, Wisconsin.

Fossil Crocodylomorphs of the National Park Service

For this year's National Park Service fossil group inventory, I've chosen crocodylomorphs, which for convenience I'm going to refer to as "crocs". Crocodylomorpha encompasses the true crocodilians and their closest extinct relatives, which over the years has been defined to exclude major groups of allied Triassic archosaurs (rauisuchids, poposaurs, prestosuchids, etc.). (Technically speaking, traditional Crocodilia is closer to the clade Crocodyliformes, but I have a soft spot for "sphenosuchians" and it's my blog.) Non-crocodilian crocodylomorphs were big players throughout the Mesozoic but came to peter out in the Cenozoic, with holdouts into the Miocene (Sebecosuchia). Some of these non-crocodilian crocodylomorphs looked basically like modern crocodilians and presumably filled very similar niches, but by definition weren't crocodilians*. Others were quite a bit different; for example, small, long-legged terrestrial crocs had a wide distribution from the Late Triassic through the Jurassic, and there were multiple groups of marine forms.

*I have certain misgivings about crown groups, particularly that future stability of usage relies on groups not going extinct (or there would have to be backdating, like radiocarbon dates are pegged to 1950), although at this point I might as well complain about the decline in use of Etruscan.

The NPS record of croc fossils turns out to be sparser than I expected: there are 17 park units with solid records (albeit two of these being reworked or washed up, making them hard to place stratigraphically), and another couple potential records. Here is the requisite map and its accompanying long caption:

Click to embiggen. The sites mentioned in this post are: 1. John Day Fossil Beds National Monument; 2. Bighorn Canyon National Recreation Area; 3. Fossil Butte NM; 4. Dinosaur NM; 5. Colorado NM; 6. Curecanti NRA; 7. Bryce Canyon National Park; 8. Glen Canyon NRA; 9. Petrified Forest NP; 10. Chaco Culture National Historical Park; 11. Theodore Roosevelt NP; 12. Badlands NP; 13. Agate Fossil Beds NM; 14. Niobrara National Scenic River; 15. Big Bend NP; 16. Waco Mammoth NM; 17. Gateway NRA; 18. Fort Washington Park; 19. Cumberland Island National Seashore.

These 19 units are primarily in the Colorado Plateau and northern Great Plain, and these two areas correlate in large part to temporal distribution: the Colorado Plateau records are mostly Jurassic and Cretaceous, and the Great Plains records are Cenozoic. A couple of compact diagrams will show this:

Part 1 shows the Mesozoic, Paleocene, and Eocene records, which make up the bulk of the reports.

Part 2 shows the few younger records; the two that can't be pinned down are added to keep them company.

You can probably guess a lot of the story if you have some familiarity with the stratigraphy of western North America. As so many other groups of terrestrial vertebrates, the place to go in the NPS for Triassic crocs is Petrified Forest National Park, where "sphenosuchians" have been found in the famous Chinle Formation. (Ignore the phytosaurs; they only look like crocs.) After that, possible early croc tracks have been found in the Navajo Sandstone of Glen Canyon National Recreation Area; with all of the Early Jurassic tracks in the Colorado Plateau parks, there are likely other track records. We have no body fossil records in the parks' rocks yet, though (the facies aren't as forgiving as elsewhere). Four parks have records for the Late Jurassic: Bighorn Canyon National Recreation Area has swim traces attributed to crocs in the Sundance Formation, and no points for guessing what's represented at the other three. (It's the Morrison Formation.) NPS Morrison crocs are best known from Dinosaur National Monument, which primarily has the well-represented Amphicotylus (formerly Goniopholis), but also produced the type specimen of the diminutive Hoplosuchus kayi.

The Cretaceous is more sparsely represented, with nothing confirmed from the Early Cretaceous. Ot the Late Cretaceous records, neither Bryce Canyon NP (Straight Cliffs and Wahweap microvertebrate remains) nor Chaco Culture National Historical Park (Menefee isolated material) have much to speak of. Big Bend NP, on the other hand, has the most impressive croc record in the NPS. Granted, that's an easy call when you can point to the type specimen of the suitably Texas-sized Phobosuchus riograndensis (now a species of Deinosuchus), but the park also has by far the longest record of crocs in the NPS. Five formations are represented: the Aguja Formation and Javelina Formation, both Late Cretaceous; the overlying Black Peaks Formation, which straddles the Cretaceous and Paleocene; the Early Eocene Hannold Hill Formation; and the Middle Eocene Canoe Formation. Recently a second croc species has been named from Big Bend NP fossils: Bottosaurus fustidens, from the Paleocene part of the Black Peaks Formation. Other taxa are present, but have not been studied in as much detail.

Looking elsewhere in the Paleocene, there is a single record of a partial bone from the Aquia Formation at Fort Washington Park, and Theodore Roosevelt NP has crocs in the Bullion Creek and Sentinel Butte Formations, comparable to nearby Wannagan Creek (only not quite so concentrated). The Eocene is fairly good for NPS crocs. Apart from Big Bend, we have croc fossils in: the Wasatch Formation at Fossil Butte NM; the Clarno Formation at John Day Fossil Beds NM; and the Chadron Formation at Badlands NP. The type specimen of Caimanoidea visheri (now considered a synonym of Alligator prenasalis) may have come from Badlands NP.

And that's almost the end. Crocs disappeared from the drying interior of North America during the middle Cenozoic. For the Miocene, we have one *very* sketchy potential record from the early Miocene Anderson Ranch Formation of Agate Fossil Beds NM and better records of crocs from the middle Miocene Valentine Formation of Niobrara National Scenic River (including the type specimen of Nordenosaurus magnus, originally described as a big lizard but now identified as a small crocodilian). At Waco Mammoth NM there is late Pleistocene alligator material, but we are otherwise lacking Pleistocene crocodilian records. Two units have material of uncertain provenance: a scute found in dredge material at Cumberland Island National Seashore and various croc fossils that have washed up at Gateway NRA.

The Lost Fucoids of Edwin McKee

Okay, that's hyperbole. The fucoids were never lost, they were just overlooked.

Many of you have probably heard of Edwin "Eddie" Dinwiddie McKee, who was the park naturalist at Grand Canyon National Park from 1929 to 1940. He moved on to other positions, but the Canyon was never far behind him. By the end of his career he'd written monographs about almost all of the Paleozoic sedimentary formations of the canyon, missing only the Temple Butte Formation and Hermit Shale/Formation for a complete set. He doesn't seem to have focused much on the Precambrian sedimentary rocks, though. Maybe the logistics of access made them less appealing (you have to go all the way to the bottom to see them, after all). Maybe the relative paucity of non-microscopic fossils made them harder to interpret. Maybe he just wasn't interested in the Precambrian. We do, though, have an interesting assortment of Precambrian rocks collected and briefly described by McKee.

In May 1930, McKee paid a visit to the Chuar Creek/Lava Creek area of eastern Grand Canyon NP, returning with about two dozen specimens from the Dox Formation, part of the Mesoproterozoic Unkar Group (lower chunk of the park's famous Grand Canyon Supergroup). Several had intriguing spindle-shaped surficial pits and ridges. McKee gave a brief description of them in an article about "fucoides" at Grand Canyon (McKee 1932). "Fucoid" goes back to the 19th century proposition that what we now know as invertebrate burrow fossils were actually seaweed fossils. (Usually the plural is "fucoids", not "fucoides") By the early 1930s, this was pretty raggedy, as McKee acknowledged; he was using it as a term of convenience for "any structure of that general nature regardless of its origin." Among the "fucoides" he presented were spindle-shaped markings on two pieces of Dox Formation rock. A careful examination of the photo will reveal that the markings in the piece on the left are incised into the rock, and those on the right-hand piece project out of the rock. They're something like mud cracks, but are certainly not textbook cracks (McKee also notes that there *are* more typical mud cracks in the Dox).

"Grant" is noted NPS photographer George A. Grant. Somewhere there must be a higher-quality version of this photo, but I haven't found it yet (I've seen one of the next figure in the article, but not this one).

This is the last we hear of these Dox "fucoides" from McKee, and probably the last anyone who was not a Grand Canyon National Park museum curator thought about them until 2019, when we began the Grand Canyon National Park paleontological inventory. I was working on the Precambrian paleontology chapter, and I love the historical side of the science, so McKee's article was right up my alley. I included the photo in my draft, and one of the reviewers noted, quite accurately, that there was no scale. Well, I couldn't do much about it (there isn't even a "photo is 2/3rd actual size" or something like that, and my time machine is in the shop, plus I don't do temporal paradoxes). That fall, though, when I was at the park I had the opportunity to visit the museum collections, and there they were. I took them outside to mimic the original photo, which appears to have been taken in front of a step, retaining wall, or something along those lines (of course including a scale bar this time).

It's not quite the same, but you get the idea. The white object is a box I used to provide additional support for the piece on the left, which at some point had been broken in two with the two pieces given different specimen numbers (the new numbers have yellowish backgrounds, while the original numbers have white backgrounds; if you compare this to the original photo, you can see the same spots).

While I was working, a number of other paleontologists were also visiting the collections as part of our National Fossil Day event. Spencer Lucas observed that the specimens looked a lot like microbially induced sedimentary structures (MISS), and asked about writing a short paper about them, to which I agreed (Tweet and Lucas 2021). The specimens themselves turned out to be more complex than is apparent from either photo. They are actually part and counterpart: in the color photo above, the large gray redox spots on the margins of the two pieces are the same spot, and the concave and convex features fit quite nicely when the pieces are lined up properly. Furthermore, there is another piece that belongs to this group, not included in the original photo (perhaps it didn't fit the composition?).

Here's a group shot, with the redox spots lined up and the previously omitted piece included.

The matching surfaces are laced with spindle-shaped features, convex in the upper row in the previous photo, concave in the lower row. Most of them are around 20 to 30 mm long (a little more or less than an inch), about 5 mm across, and with less than 5 mm of relief. A gentle, roughly longitudinal warp is most evident in the two left pieces, which might be a ripple or something similar but is heavily obscured. Flipping them over revealed additional but different features, a combination of blebs and long stringy features.

Figure 5 in Tweet and Lucas (2021). The black arrows in A point to two potential generations of ripples, and the white arrow points to the edge of a bed. B, the lower row in the preceding photo, is particularly marked by equant convex blebs and long stringy features, but there are a few on A as well.

The spindle-shaped features on the part-counterpart surfaces are shrinkage cracks, but as noted they aren't your typical mud cracks. Mud and coarser-grained sediments respond to shrinkage differently; mud grains stick to each other until something gives and a fissure forms, but sand grains slide apart from each other and do not form cracks unless something else interferes. That "something else" can be abiotic or, more frequently, biotic, such as a sticky microbial mat (Seilacher 1999). Something that is counterintuitive about microbially mediated cracks is that they are often preserved as positive features (Eriksson et al. 2007): mat and substrate contract and fissure, sediment fills fissure (either from above or from below due to environmental pressure), mat decays, and presto!—positive cracks! The long linear features in the photo above are similar to a different kind of MISS, in this case rolled-up mat fragments (Donaldson 1967; Eriksson et al. 2007).

This is more of a preliminary assessment than a definitive study. We don't have much to go on for the original geologic context, for one thing, and for another, if you really want to cover all of your bases, you need to take thin sections; MISS and inorganic features can be easily confused. Regardless, the features are highly suggestive of MISS, and the Dox Formation is already known to have stromatolites in other beds (Stevenson and Beus 1982). The Precambrian of the Grand Canyon has produced many features that were originally reported as burrow-like or "fucoidal", but most non-stromatolite features were dismissed as inorganic in the 1960s and 1970s, a couple of decades before the study of MISS took off. I would not be surprised if new study of the various formations of the Grand Canyon Supergroup, attuned to the possibility of MISS, were to uncover them in intervals previously regarded as barren of fossils.

References

Donaldson, J. A. 1967. Precambrian vermiform structures: a new interpretation. Canadian Journal of Earth Sciences 4:1273–1276.

Eriksson, P. G., H. Porada, S. Banerjee, E. Bopuougri, S. Sarkar, and A. J. Bumby. 2007. Mat-destruction features. Pages 76–105 in J. Schieber, P. K. Bose, P. G. Eriksson, S. Banerjee, S. Sarkar, O. Catuneanu, and W. Altermann, editors. Atlas of microbial mat Features preserved within the clastic rock record. Elsevier, Amsterdam.

McKee, E. D. 1932. Some fucoides from Grand Canyon. Grand Canyon Nature Notes 7(8):77–81.

Seilacher, A. 1999. Biomat-related lifestyles in the Precambrian. Palaios 14:86–93.

Stevenson, G. M. and S. S. Beus. 1982. Stratigraphy and depositional setting of the upper Precambrian Dox Formation in Grand Canyon. Geological Society of America Bulletin 93:163–173.

Tweet, J. S., and S. G. Lucas. 2021. Re-evaluation of Precambrian “fucoids,” microbially induced sedimentary structures in the Proterozoic Dox Formation, Grand Canyon National Park, Arizona. New Mexico Museum of Natural History and Science Bulletin 82:427–435.