Fossils of the Upper Ordovician Platteville Formation in the Upper Midwest USA: An Overview

I'm not really in the business of plugging books, but I *have* gotten one recently that those of you who read this blog for the Ordovician posts may find interesting (if you haven't already come across it). The book is "Fossils of the Upper Ordovician Platteville Formation in the Upper Midwest USA: An Overview" by Dennis Kolata, Illinois State Geological Survey emeritus (and also one of the authors on a volume on the Deicke K-bentonite). I was tipped off to it by member "connorp" on The Fossil Forum during my quest to identify what turned out to be Zittelloceras.

The Platteville of Illinois and southern Wisconsin isn't *exactly* the same as in Minnesota (the strata are thicker and the fossils are better preserved than what we see in the Twin Cities), but anyone looking for information or comparative photos for Minnesota Platteville fossils is going to find plenty in the book to consider. The book is also useful for identifying fossils in the overlying rocks (e.g., the Decorah Shale), because many of the genera are the same. Several graphics clarify the correlation of different Platteville divisions across the area where the formation was deposited.

The text, organized by broad taxonomic group, is technical. Each species is given a diagnosis, followed by remarks about aspects such as notable features or distinguishing it from other species, and then its stratigraphic and geographic distribution. This is not unlike the various group-focused articles in Sloan (1987), but unlike the small black-and-white figures in the 1987 book, Kolata's book is filled with gorgeous color plates featuring large photos of every species. (The one quibble I have is that scaling is given by numbers, e.g., "x1.5", instead of scale bars, but I can certainly use them either way!) For anyone who is interested in the fossils but is not versed in the details of invertebrate anatomy, or anyone just looking to identify a particular find, these plates are invaluable.

If you'd like to find out more about this volume, the Illinois State Geological Survey bookstore is online here. The book can also be found on Amazon. It is 316 pages and costs $60.00.

References

Kolata, D. R. 2021. Fossils of the Upper Ordovician Platteville Formation in the upper Midwest USA: an overview. Illinois State Geological Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign, Champaign, Illinois. Bulletin 108.

Sloan, R. E., editor. 1987. Middle and Late Ordovician lithostratigraphy and biostratigraphy of the Upper Mississippi Valley. Minnesota Geological Survey, St. Paul, Minnesota. Report of Investigations 35.

Fossil Collections of the Ancestral Puebloans

Although the ancient biological origin of fossils has only been widely appreciated in the past couple hundred years, people have collected fossils for various reasons for millennia. One of my favorite instances is recorded by Roman biographer Suetonius, who noted that Augustus had a collection of bones of "sea and land monsters" at Capri. (By the way, if you're also a sucker for ancient history as written by ancient historians, "The Twelve Caesars" is a great book.)

One of the things I've come across working with National Park Service paleontology is that the Ancestral Puebloans, represented by numerous locations in the NPS, had a notable interest in fossils. This is something that took a while for me to realize because most of the evidence is in the archeological literature and as a paleontologist, I didn't know to look in it. On the flip side, the archeologists generally didn't make a big deal of finding run-of-the-mill fossils among the artifacts at their sites; for them, fossils were just one class of objects among many. I haven't made an exhaustive survey, but a couple of sites stand out.

Pecos Pueblo is the namesake feature of the complex Pecos National Historical Park. The pueblo was excavated between 1915 and 1925 by Alfred Vincent Kidder of the Robert S. Peabody Museum of Archaeology (Phillips Academy, Andover, Massachusetts). Kidder (1932) reported finding "many hundreds" of fossils at Pecos Pueblo. They were predominantly marine fossils from "the limestone formations underlying the red sandstones of the valley", which appears to correspond to the Pennsylvanian-age Alamitos Formation of the Madera Group. Among these were corals, brachiopods ("bivalves" of the photo caption), snails, and crinoids. Not all were marine; among them was a partial rhino tooth, and there were also many pieces of petrified wood, including colorful Chinle wood and brown or gray wood typical of the area southwest of Santa Fe, possibly selected for its unusual cleavage and the "clear, resonant tone which it gives when tapped". Kidder observed that the majority of the fossils were found in rubbish and suggested they were collected as curios, but I have to wonder. It takes some effort to collect hundreds of fossils (although admittedly Pecos Pueblo was inhabited for a long time).

Pecos Pueblo is hardly a patch on Pueblo Bonito of Chaco Culture National Historical Park, though. Pepper (1920) documented fossils in 18 rooms, not counting artifacts made of petrified wood. Most had just a few, but Room 12 is something else. Room 12 has a floor area less than 10 square meters (108 square feet; a bit less than 3.7 by 2.7 m or 12 ft by 9 ft), and when excavated contained a 1.5 m (5 ft) thick layer including the following:

• 1,000+ small fossil shells
• 300 fragments of crinoid stems
• 140+ water-worn pebbles
• 125+ chalcedony concretions
• 125+ fragments of contemporary Pacific shells
• 50 to 75 specimens of crystals or other rocks and minerals of beauty or interesting form

This is the largest intentional accumulation of fossils predating the rise of museums that I've come across. Furthermore, unlike Pecos Pueblo, a significant chunk of the paleontological collection could not have been collected more or less "in the backyard". Judd (1954) provided taxonomic identifications of some of the fossils from a re-excavation. Chaco Canyon is over Campanian (Late Cretaceous) bedrock. The taxa identified from Room 12 include several Pennsylvanian-age brachiopod species known from central New Mexico, a Cenomanian ammonite (Metoicoceras whitei) with its nearest occurrences in the Black Mesa area of Arizona, and a snail (Gyrodes compressa/Euspira compressa) known from Upper Cretaceous rocks of the Pacific coast of California. This is a gathering of fossils that took some effort.

What exactly were the inhabitants of Pueblo Bonito doing with 1,300+ fossils? Agostini and Notterpek (2020) suggest that the fossil shells, together with the water-worn pebbles and concretions, were symbolic of water and a "past watery world". The canyon itself would also be symbolic of the action of water. It's an interesting idea, although again I do marvel at the sheer number of fossils. The scientific romantic in me wonders if there was someone there who just found fossils and minerals interesting, maybe even had them arranged in some pleasing setup (even sorted by morphology), and perhaps cultivated the collection of rare and unfamiliar objects. Or, maybe concentrating all of those fossils in one small place amplified their power. Or, maybe it was something like a museum, or at least a place to display and contemplate these objects. But what do I know?

References

Agostini, M. R., and I. Notterpek. 2020. Cosmological expressions and medicine stones in the Ancestral Pueblo world. KIVA 86:(4):4030–427. doi: https://doi.org/10.1080/00231940.2020.1832406.

Judd, N. M. 1954. The material culture of Pueblo Bonito. Smithsonian Miscellaneous Collections 124.

Kidder, A. V. 1932. The artifacts of Pecos. Yale University Press, New Haven, Connecticut.

Pepper, G. H. 1920. Pueblo Bonito [large file]. Anthropological Papers of the American Museum of Natural History 27.

G. Suetonius Tranquillus. 121. The twelve Caesars. Penguin Books, London, England. 1989 reprint of 1957 translation by Robert Graves.

Zittelloceras

While on a walk earlier this year, I spotted a Decorah block that I decided to pick up for photography. The initial attraction was the abundance of snails, which are a reliable indicator that pieces of our fossil arthropod friends are also present (if there's only one practical thing you take away from this blog, it's "when you're in the Decorah and see snails, look for trilobites"). This was indeed the case:

Here's the whole block, which rewards a click to embiggen. There is a nice Clathrospira and a lophospire just right of the scale bar, and many smaller snails scattered throughout. You may also pick out the trilobite pygidia.

Here's a pygidium, pointed toward the top of the photo.

A nice pygidium plus a number of other things, including some crinoid columnals, bryozoan fragments, other trilobite bits, and, near the top, a whorl of a snail.

There was also something else: a dark object several millimeters long and broad. It appeared to be a thin-walled flattened tubular object, with a distinct series of ornamented transverse ridges. The ridges showed an alternating pattern of strongly projecting and more subtle, like perforations. Both had little scooped frilling, the same kind of shape as a doodle of stereotypical ocean waves.

The object in question is near center. You may have noticed it in the first photo. The light-colored band near the center is some light prep to see if I could get the matrix out from the groove.

I'd never seen this combination of features before, but I could knock out a lot of things quickly. In fact, I knocked out just about everything, which was a problem. Given the probability I had discovered a completely new phylum is pretty low, all things considered, I figured I'd probably missed something. So, I pulled out my copy of "A Sea Without Fish" (Meyer and Davis 2009) to see if some similar exotica had been found in the well-studied Cincinnatian, as it's only a few million years younger. Then I got excited looking at the figure and description of the machaeridian worm Lepidocoleus. Machaeridia is an extinct group of Paleozoic armored annelid worms, with segments of calcitic plates and a heart-shaped cross-section.

This view, under different lighting, shows the ridges and frills to good effect.

Before I got too excited, I decided to put it up on the Fossil Forum, to see what others might think. The first suggestion was Phragmolites, which was reasonable enough but didn't fit my experience with that snail. The chunk wasn't curved enough, the dark coloration and thin wall were unlike the examples of Phragmolites I'd seen, and the ornamentation of the ridges wasn't a good fit. Then someone came up with the nautiloid Zittelloceras, and provided photos of a form with almost the exact same pattern of frilled ridges found in the Platteville.

An end-on view shows the cross-section, with the thin walls and central crushing.

So, it looks like rather than a worm, it's a nautiloid. Zittelloceras is one of the "arched" nautiloids, not coiled and not a full-on orthocone. Several species are present in the Platteville per Catalani (1987), but none are listed in the Decorah. This is not a particular problem, as the genus is present in younger strata as well, and the Decorah's cephalopod record lags the Platteville. (Note that Zittelloceras is frequently misspelled "Zitteloceras", with one "l", but a look at the original publication, Hyatt 1884, shows the two-l spelling is correct.) I'm sure there are worms out there to be found in the Decorah, but I'll settle for this record of an ornate nautiloid.

Here's one more angle for the road.

References

Catalani, J. A. 1987. Biostratigraphy of the Middle and Late Ordovician cephalopods of the Upper Mississippi Valley area. Pages 187–189 in R. E. Sloan, editor. Middle and Late Ordovician lithostratigraphy and biostratigraphy of the Upper Mississippi Valley. Minnesota Geological Survey, St. Paul, Minnesota. Report of Investigations 35.

Hyatt, A. 1884. Genera of fossil cephalopods. Proceedings of the Boston Society of Natural History 22:253–338. [some history: The paper is based on a talk presented by Hyatt April 4, 1883, a day before his birthday. There is a note on the first page that there was going to be a monograph in the Memoirs of the Museum of Comparative Zoology, but this did not happen. At any rate it's hard to think of an 80-page paper being "preliminary" to anything!]

Meyer, D. L., and R. A. Davis. 2009. A sea without fish: life in the Ordovician sea of the Cincinnati region. Indiana University Press, Bloomington and Indianapolis, Indiana.

Your Friends The Titanosaurs: Igai semkhu

This happens to be the 400th post on Equatorial Minnesota, and it's on a fitting subject, as about 15% of the posts have been on titanosaurs. In fact, this particular titanosaur has been mentioned before, as a potential coming attraction. What was referred to as MB.R.Vb-621–640 in that post now has a name: Igai semkhu. Let's have a look at what this new genus and species can tell us.

Figure 1 from Gorscak et al. (2023), including quarry map (with lost material), reconstruction, and geographic insets (CC BY-NC-ND-4.0).

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.

Vectipelta barretti

Last week we had a look at almost-hadrosaur Gonkoken nanoi. This week we're hopping over to another branch of Ornithischia for the ankylosaur Vectipelta barretti. I'm always up for ankylosaur news, and took particular interest in this case because I've long had a deep and irrational fondness for Polacanthus, going back to the 1980s.

Gonkoken nanoi

The Great Dinosaur Drought of 2022–2023 persisted from mid-December 2022 to early June 2023, nearly six months with three new dinosaurs and one silesaur, but with five showing up in the past few weeks, it looks like things have gone back to business as usual. Obviously that calls for some recognition, so this week and next week (pending anything else) I'll look at a couple of new arrivals, starting with the not-quite-hadrosaurid Gonkoken nanoi from the south end of Chile.

Figure 2 in Alarcón-Muñoz et al. (2023), showing a reconstruction of Gonkoken nanoi and an assortment of bones (CC BY 4.0).