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).

Uŋčí Makhá Park Revisited, Part 2: Further Fossils

We're now up to the fourth entry in a completely unexpected series on the Platteville–Decorah rocks and fossils of Uŋčí Makhá Park. We've already seen the common fossils from the site, so for this go-round I'm focusing on rarities.

Uŋčí Makhá Park Revisited, Part 1: Freeze-Thaw

After I'd come across the new exposures at Uŋčí Makhá Park last fall, I was very curious about how a Minnesota winter and spring would treat them. After all, these were fresh, with no previous direct exposure to snow, ice, and freeze-thaw cycles. Would they rapidly degrade, or were they made of sterner material? Last week I had the opportunity to spend some quality time at the park, in preparation for and leading a training session for Mississippi National River & Recreation Area seasonals (and if any of the participants happen on this post, hello! I hope you had a good time!).

What were the results of this natural experiment? A few observations:

The Carimona Member of the Decorah (blue-gray upper interval), particularly the blocks used as landscaping, suffered appreciably more than the Magnolia Member of the Platteville (tan lower interval). I attribute this to the greater shale content of the Carimona.

This is a pretty illustrative comparison. The blue-gray block on the upper left is Carimona, and the tan block on the lower right is Magnolia. The Carimona block's upper surface is littered with small chips, while the only chips on the Magnolia block came from the Carimona block. (Note also the large burrow on the Magnolia block.)

More Carimona landscaping showing exfoliation.

This indicates that the Carimona blocks will weather faster than the Magnolia blocks; eventually, both lithologies will reach equilibrium with their new surroundings, but the "fucoidal" surfaces on the landscaping are going to go away faster than the shell beds.

Note the burrows popping off the surface in some places.

It wasn't all smooth sailing for the Magnolia, though. Although many blocks and beds seemed fine, others had definite signs of damage.

Here a thin bed is breaking up.

This isolated block appears to be shattered. (Colors are weird because when I took this photo, I'd forgotten to reset the lighting from tungsten bulbs.)

Unlike last fall, which was a time of drought, this spring we can also definitely see where the seeps are.

And they're concentrated at the bentonite layers in the Carimona.

Many fossils and features came through without particular damage, though. I included a photo of a bivalve in the fossil guide post. Here it is last week:

Dare I say that it's "happy as a clam"? (Ignore the color balance differences.)

With that out of the way, did we find other fossils I hadn't seen in the fall? Well, of course! Tune in next week for some less-typical fossils!

Replacement of Fossils

You might think that getting a shell or bone or wood chunk safely buried is the tough part for fossilization, that once something's entombed in sediment it's all smooth sailing. Burial is certainly important, but it's not the end of the story. A lot of things can happen between deposition and exposure. Pore spaces are filled with new minerals. Existing minerals are replaced. Entire structures can be replaced, then lost. These changes all fall under diagenesis. What exactly happens depends on things like the physical and chemical structure of the object in question, temperature and pressure of burial, and the chemical composition of the fluids in the sediment. Denser fossils like teeth are less vulnerable to changes than more porous materials. The form of calcium carbonate known as aragonite is less stable than calcite. Many different minerals and mineraloids can get involved in the fun; for example, there are opalized fossils and pyritized fossils.

Bivalve mold and internal cast (steinkern). Not pictured: bivalve shell.

Because silica and carbonate minerals are so abundant at typical surface and near-surface temperatures and pressures, they are the minerals most frequently involved. In Minnesota, we generally get dolomitization. This is somewhat inconvenient, because dolomitization has a tendency to destroy fossils, and even when it doesn't, it usually leaves behind molds and casts that aren't as crisp as the original. It's a bit like replacing the Venus de Milo or Michelangelo's David with nothing but 2x4 Lego bricks; you'll notice a difference. Dolomitic replacement may give a fossil a quirky sparkly appearance thanks to the dolomite rhombs, but that's about the only plus. Pervasive dolomitization is why many fossils in the Platteville are gray with a sugary appearance: you're actually looking at a natural mold or cast of the original in dolomite.

Sometimes diagenesis gives you exotic, spectacular fossils, and sometimes it gives you dolomite.

Although once in a while you get something to write home about; this is a nautiloid in the Science Museum of Minnesota collections with its internal structures replaced.

I was inspired to write a note about this topic by a different kind of replacement. Someone reviewing one of my work projects commented on a type of replacement seen in some of the fossils, consisting of circular mineralizations. They informed me this was a kind of silicification known as beekite. This immediately twigged my memory banks, because I'd also seen it in photos of fossils from other work projects. Like dolomitization, it's not exactly faithful reproduction, although it can be aesthetically pleasing.

A beekitized (beekitified?) lower Permian brachiopod, central Kansas.

The Face of Diamantinasaurus (and some other body parts)

One of the things that was frequently missing from "Your Friends The Titanosaurs" was heads. Sure, there were a fair number of lower jaws and braincases, but actual faces were few and far between. Skulls just don't seem to have stuck with the rest of the skeleton, and in general were not made of the sternest material in a titanosaur's body. (Bitey parts of the skull, yeah, those are more robust. Braincases, yeah, those are knots of bone. Stuff in between? Not so much.) Several entire continents are unrepresented by reasonably complete titanosaur skulls. We can now scratch Australia off that list, thanks to Diamantinasaurus matildae, as described in great detail by Poropat et al. (2023).

(...or can we? See below!)

The Conulariid Interior

Today we check in with one of the more unusual members of Paleozoic seafloor communities: Conulariida. The "four-sided herringboned ice cream cones" still hold many mysteries (including the mystery of the whereabouts of George Sinclair's collection; I'd still be interested in knowing more about that!). One of the major mysteries has been what exactly the soft parts of the animal looked like; if we knew that, we'd know a lot more about how conulariids are related to other animals, how they fed, how they looked, etc. It's generally assumed they are some kind of cnidarian (along with corals, jellyfish, sea anemones, and so on). Wikipedia has them potentially aligned with Staurozoa, which today is represented by stalked jellyfish (worth looking up if you've never heard of stalked jellyfish).

A cnidarian identity would imply stinging tentacles, but these have never been firmly identified. Soft parts in general are not particularly well-known for conulariids, which makes sense because preserving the soft parts of cnidarians is not something that just happens as a matter of course. (We could use a late Paleozoic amber-producing coastal forest that was flooded by a storm that dredged up all kinds of marine organisms.) There were some potential finds in the 1980s, as discussed in Babcock and Feldman (1986a) and Sendino et al. (2023) (see Figure 30 in Babcock and Feldman 1986b for internal casts and x-ray image of a conulariid's putative guts). Recently, Sendino et al. (2023) have applied X-ray micro-Computed Tomography (μCT) to a collection of well-preserved Pennsylvanian-age conulariids from the Wewoka Formation of Oklahoma and the Finis Shale Member of the Grand Formation of Texas.

What can μCT see in a conulariid? First off, it can see the concealed end of one conulariid partially within another conulariid. This is a good sign as a sanity check because we can confirm it can discern something that obviously should be there. With that encouraging information in mind, what else is there?

Figure 4 in Sendino et al. (2023); it's always good to see what you *ought* to see. CC BY 4.0.

Sendino et al. (2023) found "longitudinal bundles" in many of their specimens, i.e., oriented apex–aperture. The authors interpreted these as muscles for closing the flaps of the aperture. (This tells us a few things about the muscular and nervous systems of conulariids.) In some examples there was also an internal structure they interpreted as a possible gastric cavity. In other specimens, the internal sediment was clearly replaced, for example by sand, or contained other fossil material such as forams or a tiny drilled brachiopod. The internal sediment of some specimens appears to have been disrupted by later burrowing. A number of the conulariids also show scars from external attacks (conulariids seem to have been easy targets). The article, which is freely available, is heavily illustrated with μCT images, followed up by a series of supplementary files of large images.

And this is their basic interpretation (Figure 13). CC BY 4.0.

In other business: I'll be giving a talk for the Geological Society of Minnesota on Monday, May 8: "Snorkeling at Shadow Falls: Fossils of Minnesota". Non-members are welcome!

References

Babcock, L. E., and R. M. Feldmann. 1986a. Devonian and Mississippian conulariids of North America. part A. General description and Conularia. Annals of the Carnegie Museum 55:349–410.

Babcock, L. E., and R. M. Feldmann. 1986b. Devonian and Mississippian conulariids of North America. part B. Paraconularia, Reticulaconularia, new genus, and organisms rejected from Conulariida. Annals of the Carnegie Museum 55:411–479.

Sendino, C., B. Clark, A. C. Morandini, T. Salge, M. Lowe, and W. Rushlau. 2023. Internal conulariid structures unveiled using µCT. PalZ (2023). doi:https://doi.org/10.1007/s12542-023-00649-7.

Prasopora, with a comment on biostratigraphy

Prasopora, the "gumdrop bryozoan", is one of the most recognizable Ordovician fossils in Minnesota. Museum collections from Minnesota have boxes of the little darlings rattling around together. And I—I hardly ever see the dang things in the field.

Yes, one of these things; a bit more "chocolate kiss" than "gumdrop" but well within morphological variation.

While my competence in many fields is questionable at best, in this case you can be assured I would recognize a Prasopora if I saw one, even if it was years before I learned the stress goes on the second syllable rather than the third. (I have an unerring instinct for putting the stress on the wrong syllable for scientific names I've read but never heard.) No, the real issue here is one of biostratigraphy. My usual stomping grounds cap in the lower third of the Decorah, and Prasopora doesn't really kick in until the middle–upper Decorah. This has been recognized since the days of "The Geology of Minnesota" (Ulrich 1895; Winchell and Ulrich 1897). At that time eight species were recognized (P. affinis, P. conoidea, P. contigua, P. insularis, P. lenticularis, P. oculata, P. selwyni, and P. simulatrix), all of which were restricted to a range extending from the "Fucoid and Phylloporina beds" of the "Black River Group" (roughly Sardeson bed 5, middle–upper Decorah) to the "Fusispira and Nematopora beds" of the "Trenton Group" (as high as Sardeson bed 8, in the Prosser Limestone) (Winchell and Ulrich 1897; approximate correlations after Sloan 1987). None of them are listed in equivalents to Sardeson beds 3 and 4, in the lower Decorah, and only P. conoidea, P. contigua, P. lenticularis, and P. simulatrix were reported from the closest "Fucoid and Phylloporina beds".

Same specimen as above, which has a convenient break showing a partial cross-section; it's not solid all the way through.

Forty years later Stauffer and Thiel (1941) were not quite as dainty in their stratigraphic divisions, simply having a Decorah Shale Member of the Galena Formation and a Spechts Ferry Member of the Platteville Formation (approximately the Carimona Member of the Decorah). The "Spechts Ferry" gets Prasopora grandis, which had been Monticulipora grandis back in 1897, when it had been reported from the Stictoporella bed (lower Sardeson bed 3). P. grandis also appears in S&T's Decorah Shale Member list along with the four "Fucoid and Phylloporina beds" species, Stauffer presumably having stratigraphically higher specimens of P. grandis than W&U. Whether or not grandis pertains to Prasopora has been a matter of some dispute, and it seems to have wandered back to the metaphorical arms of Monticulipora. More importantly, it doesn't look like classic gumdrop Prasopora, instead being "irregularly massive, often tending to become lobate or subramose" (Ulrich 1895). In other words, it's not the kind of thing the typical fossil enthusiast would associate with the genus.

Wee little discoidal Prasopora.

My personal experience with Prasopora is limited to a few pieces in the Valentine box that appear to represent P. conoidea and a small discoidal species, a couple of small discoidal specimens that blur the line between early-stage Prasopora and "less famous bryozoan encrusting the external surface of an inarticulate brachiopod in an aesthetically pleasing Prasopora-like way", and one great honking lopsided hoof of a colony I found a few years ago at a basement excavation. I don't generally attempt to assign species to bryozoan fossils, but P. simulatrix is the only species described by Ulrich (1895) to attain dimensions even vaguely like it, so I'll go with that.

A top view of an unfortunately resolutely three-dimensional object.

And the underside, showing the distinctive layering and a few bits of other things that became part of the structure.

Bonus news: for those of you who've had your fill of gumdrop bryozoans, the spring 2023 edition of the NPS Park Paleontology newsletter is now available.

References

Sloan, R. E. 1987. History of study of the Middle and Late Ordovician rocks of the Upper Mississippi Valley. Pages 3–6 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.

Stauffer, C. R., and G. A. Thiel. 1941. The Paleozoic and related rocks of southeastern Minnesota. Minnesota Geological Survey, St. Paul, Minnesota. Bulletin 29.

Ulrich, E. O. 1895. On Lower Silurian Bryozoa of Minnesota. Pages 96–332 in L. Lesquereux, C. Schuchert, A. Woodward, E. Ulrich, B. Thomas, and N. H. Winchell. The geology of Minnesota. Minnesota Geological and Natural History Survey, Final Report 3(1). Johnson, Smith & Harrison, state printers, Minneapolis, Minnesota.

Winchell, N. H. and E. O. Ulrich. 1897. The lower Silurian deposits of the Upper Mississippi Province: a correlation of the strata with those in the Cincinnati, Tennessee, New York and Canadian provinces, and the stratigraphic and geographic distribution of the fossils. Pages lxxxiii–cxxix in L. Lesquereux, C. Schuchert, A. Woodward, E. Ulrich, B. Thomas, and N. H. Winchell. The geology of Minnesota. Minnesota Geological and Natural History Survey, Final Report 3(2). Johnson, Smith & Harrison, state printers, Minneapolis, Minnesota.

Brooksella: what are star cobbles?

Back in the far-off year of 2012, when I was helping to compile instances of paleontological type specimens found in National Park Service units, we had to make decisions about various edge cases. One of these was how to handle names for what later turned out to be pseudofossils. We decided to record the information as historically relevant but did not include the "taxa" in any counts. On this blog we've actually covered a couple of them already, "Lingula calumet" and "Paradoxoides barberi" from within or very near Pipestone National Monument. Another is "Brooksella canyonensis", a putative jellyfish from the Proterozoic Nankoweap Formation of Grand Canyon National Park. It was first reported as such in Van Gundy (1937) and then named, not entirely enthusiastically, in Bassler (1941). "B. canyonensis" has fared poorly as a jellyfish, but has had its supporters as an organic feature (e.g., Glaessner 1969; Kauffman and Steidtmann 1981; Kauffman and Fursich 1983; tentatively Ciampaglio et al. 2006). However, I favor an inorganic interpretation. Admittedly, there are several to choose from: gas-escape structures or compaction (Cloud 1968), "sand-volcano"-type fluid escape (Ford and Breed 1977; Ford 1990), and mud rolls (Fedonkin and Runnegar 1992).

"B. canyonensis" was not the first species in the genus Brooksella, though. Brooksella was named by Charles Walcott for "star cobbles" from the Coosa Valley of Alabama (Walcott 1896), now attributed to the middle Cambrian-age Conasauga Formation (Nolan et al. 2023). In fact, he named three taxa for different forms of cobbles: B. alternata, B. confusa, and Laotira cambria (Walcott 1896). Star cobbles got their name because at their best they look like the stereotypical twinkly pointed things you might doodle. Some of them even have five rays, although six is more typical and they are more lobed than pointed, so it's not a perfect match.

Brooksella (A–D, K) and Laotira (E–H, J) as illustrated by Walcott (1898) and reproduced as Figure 1 in Nolan et al. (2023) (which see for full caption). CC BY 4.0.

Walcott interpreted the objects as representing jellyfish, which are probably not the first thing you think of when fossils come to mind, but jellyfish fossils are in fact known elsewhere. In this case, though, the interpretation hasn't proved tremendously popular over time, and numerous alternatives have been proposed. These alternatives, though, generally involve some kind of organic origin, either as a true body fossils or a trace fossil of some sort. It's not hard to see why: they look like something that *ought* to be organic, even if the identity of that something is unclear. (Anyone who has gone out fossil hunting will probably recognize this feeling. Sometimes you're right, sometimes you're wrong.)

Nolan et al. (2023) have published a detailed reassessment of Alabama Brooksella. As part of it, they prepared a lovely supplemental figure of various hypotheses, with thumbnail evaluations (discussed at greater length in the text). (*Warning*: Hold off on clicking the link if you'd rather not get their solution immediately.) Studies of Brooksella from the past couple of decades have interpreted it as a trace fossil (either a feeding burrow or a coprolite) or a glass sponge (hexactinellid). Nolan et al. subjected star cobbles to about as many tests as can legally be done to rocks in their analysis of the various possibilities, and came to several conclusions, including:

• Brooksella specimens do not have a sponge's anatomy. There aren't spicules, features previously interpreted as ostia (pores) bear a strong resemblance to pitting left behind when lichen are cleaned off, and lobes do not feature opening at their ends for radial canals (which were also not found).
• The orientation of the specimens when found in situ was with the putative central osculum (excurrent vent) down in the sediment, which is an inconvenient place for an osculum. Furthermore, many examples did not even have an "osculum".
  
• The specimens include internal voids and tubes, but these spaces do not correspond to the external form, unlike primary burrows (although this does not preclude the specimens having "captured" parts of burrows that were passing through). Furthermore, the internal features do not include common burrowing structures such as backfill.
  
• The specimens have the same composition as silica concretions from the same rocks, and are very comparable overall, with the same kind of weathering rings, lichen pitting, and random internal voids and tubes.
  

Nolan et al. concluded that Brooksella is no different from the local concretions except for the lobes, and should therefore "be considered a pseudofossil until proven otherwise." A consequence of this conclusion is that Brooksella, not being a glass sponge, would not have been a source of silica for preservation of fossils in the Conasauga. (It's not stated, but it seems that it would have been a sink instead.) It further goes to show that you shouldn't trust strange things in the Cambrian.

Brooksella (A–E) and concretions (F–K) collected from the Conasauga Formation by Nolan et al. (scale bar 1 cm, or 0.4 in); Figure 5. CC BY 4.0.

References

Bassler, R. S. 1941. A supposed jellyfish from the pre-Cambrian of the Grand Canyon. Proceedings of the United States National Museum 89(3104):519–522.

Ciampaglio, C. N., L. E. Babcock, C. L. Wellman, A. R. York, and H. K. Brunswick. 2006. Phylogenetic affinities and taphonomy of Brooksella from the Cambrian of Georgia and Alabama, USA. Palaeoworld 15:256–265.

Cloud, P. E., Jr. 1968. Pre-metazoan evolution and the origins of the Metazoa. Pages 1–72 in E. T. Drake, editor. Evolution and environment. Yale University Press, New Haven, Connecticut.

Fedonkin, M. A., and B. N. Runnegar. 1992. Proterozoic metazoan trace fossils. Pages 389–395 in J. W. Schopf and C. Klein, editors. The Proterozoic biosphere: A multidisciplinary study. Cambridge University Press, Cambridge, United Kingdom.

Ford, T. D. 1990. Grand Canyon Supergroup: Nankoweap Formation, Chuar Group, and Sixtymile Formation. Pages 49–70 in S. S. Beus and M. Morales, editors. Grand Canyon geology. Oxford University Press, New York, New York.

Ford, T. D., and W. J. Breed. 1977. Chuaria circularis Walcott and other Precambrian fossils from the Grand Canyon. Journal of the Palaeontological Society of India 20:170–177.

Glaessner, M. F. 1969. Trace fossils from the Precambrian and basal Cambrian. Lethaia 2(4):369–393.

Kauffman, E. G., and F. Fursich. 1983. Brooksella canyonensis: A billion year old complex metazoan trace fossil from the Grand Canyon. Abstracts with Programs - Geological Society of America 15(6):608.

Kauffman, E. G., and J. R. Steidtmann. 1981. Are these the oldest metazoan trace fossils? Journal of Paleontology 55:923–947.

Nolan, M. R., S. E. Walker, T. Selly, and J. Schiffbauer. 2023. Is the middle Cambrian Brooksella a hexactinellid sponge, trace fossil or pseudofossil? PeerJ 11:e14796. doi:https://doi.org/10.7717/peerj.14796.

Van Gundy, C. E. 1937. Jellyfish from Grand Canyon Algonkian. Science 85(2204):314.

Walcott, C. D. 1896. Fossil jelly fishes from the Middle Cambrian Terrane. Proceedings of the United States National Museum 18:611–614.

Walcott, C. D. 1898. Fossil Medusæ. U.S. Geological Survey, Washington, D.C. Monograph 30.

Your Friends The Titanosaurs: Chucarosaurus and (maybe) Ruixinia

We check in again with titanosaurs with one new genus and species that is definitely titanosaurian, and another that falls into the hazy uncertainty of potential Early Cretaceous titanosaurs.

Chucarosaurus diripienda

It's been a thing the past couple of years for dinosaurs to take the winter off, with few new names in December, January, and February, and 2023 has continued the tradition. Also, oddly enough, titanosaurs seem to strike during the winter; not that any time of the year is safe from them, but you can count on them taking up the slack left by tyrannosaurs and duckbills and so on.

Where was I? Anyway, the first publicized non-avian dinosaur of 2023 is our first guest, the titanosaur Chucarosaurus diripienda.

Genus and Species: "Chucaro" is a Quechua word for a "hard and indomitable animal", while "diripienda" is Latin for "scrambled" (Agnolin et al. 2023), giving us something like "scrambled indomitable lizard".

Citation: Agnolin, F. L., B. J. Gonzalez Riga, A. M. Aranciaga Rolando, S. Rozadilla, M. J. Motta, N. R. Chimento, and F. E. Novas. 2023. A new gigant titanosaur (Dinosauria: Sauropoda) from the Upper Cretaceous of northwestern Patagonia, Argentina. Cretaceous Research (preprint). doi:https://doi.org/10.1016/j.cretres.2023.105487.

(Thank you to Matias Motta for providing a pdf!)

Stratigraphy and Geography: C. diripienda is to date known only from the lower Upper Cretaceous Huincul Formation of the Pueblo Blanco Natural Reserve, northwestern Río Negro Province, Argentina (Agnolin et al. 2023). The site is rather better known for a variety of theropods representing several lineages (Tralkasaurus, Aoniraptor, Gualicho, Taurovenator, Overoraptor) (Agnolin et al. 2023).

Holotype: MPCA (Museo Provincial "Carlos Ameghino", Cipolletti, Río Negro, Argentina) PV 820, consisting of a left humerus, most of a left radius, left metacarpal II, left ischium, somewhat eroded left femur, the shaft of the left fibula, the proximal end of the right tibia, and the distal end of an anonymous metapodial, found disarticulated but associated and interpreted as representing one individual (Agnolin et al. 2023). A left femur and tibia (MPCA PV 821) represent another individual.

You might notice right away that, unlike most titanosaurs, we're not dealing with vertebrae here. This is a little inconvenient for comparative purposes, but on the other hand it does focus attention on areas of titanosaurian anatomy that do not receive as much attention. The limb bones indicate a large but relatively gracile form, with an estimated femur length of 200 cm (78.7 inches) (Agnolin et al. 2023).

Two other titanosaurs have been named from the Huincul Formation, the redoubtable Argentinosaurus huinculensis and the somewhat less famous Choconsaurus baileywilsoni. Limb bones of A. huinculensis and C. diripienda can be distinguished by several details, as well as A. huinculensis being more robust overall (although I suppose that shouldn't be too surprising). There is very little overlap with C. baileywilsoni, only metacarpal II, which is much more elongate in C. baileywilsoni. The phylogenetic analysis places C. diripienda as a colosssaurian but not quite a lognkosaurian, hanging out in the area of Bonitasaura salgadoi and Notocolossus gonzalezparejasi (Agnolin et al. 2023).

Ruixinia zhangi

Oddly enough again, the last non-avian dinosaur of 2022 was a potential titanosaur, Ruixinia zhangi. It falls into the grand tradition of Early Cretaceous East Asian titanosaur-ish sauropods, and as such is well worth an entry.

Genus and Species: The entire name is an allusion to Ruixin Zhang, a benefactor of the Erlianhaote Dinosaur Museum (Mo et al. 2023). As such, a translation isn't really applicable.

Citation: Mo, J., F. Ma, Y. Yu., and X. Xu. 2023 (preprint 2022). A new titanosauriform sauropod with an unusual tail from the Lower Cretaceous of northeastern China. Cretaceous Research 144:article 105449. doi:https://doi.org/10.1016/j.cretres.2022.105449.

(Cretaceous Research could almost be sub-headed as "The Journal of Titanosaurian Research" these days. They're all over it.)

Stratigraphy and Geography: R. zhangi hails from the famous Yixian Formation and was found at Batuyingzi, Beipiao, western Liaoning Province, northeastern China (Mo et al. 2023).

Holotype: ELDM (Erlianhaote Dinosaur Museum, Inner Mongolia, China) EL-J009, an articulated partial skeleton featuring most of the vertebrae (14 cervicals, dorsals, several sacrals, and 52 caudals), several dorsal ribs, 36 chevrons, left hip minus the ischium, left femur, left tibia, left astragalus, left metatarsal V, and a possible pedal phalanx (Mo et al. 2023).

Going from the description of the holotype, you'll note that we're dealing with a nearly complete vertebral column. Unfortunately, the other side of the coin in this case is that the precaudals are rather smooshed (Mo et al. 2023). From a visual inspection the cervicals seem kind of chunky, suggesting a relatively thick neck. R. zhangi has a rather odd tail; some of the highlights are as follows. The anterior caudals are strongly procoelous. The last six caudals are fused into a rod, simple in structure unlike the club of Shunosaurus and the cockscombs of Mamenchisaurus hochuanensis (Mo et al. 2023). (If it's just a rod, I wonder if it's just a one-off pathology.) The caudal neural spines are notably low and mildly split at the tops in the anterior caudals; the supporting neural arches are not cheated anteriorly in the first part of the tail like most titanosaurs but do have an anterior bias later on (Mo et al. 2023).

R. zhangi is not particularly large, with a femur 137 cm (53.9 inches) long and an overall body length on the order of 12 m (39 ft), but it is the current champion of the Yixian Formation sauropods (followed by Dongbeititan with a femur length of about 114 cm [44.9 inches] and Liaoningotitan slightly smaller at 108 cm [42.5 inches]). The phylogenetic analysis finds it well within Titanosauria (Mo et al. 2023), which is promising, but it's also closely associated with two taxa that are questionably titanosaurian per other authors (Daxiatitan and Xianshanosaurus), which is not so promising.

References

Agnolin, F. L., B. J. Gonzalez Riga, A. M. Aranciaga Rolando, S. Rozadilla, M. J. Motta, N. R. Chimento, and F. E. Novas. 2023. A new gigant titanosaur (Dinosauria: Sauropoda) from the Upper Cretaceous of northwestern Patagonia, Argentina. Cretaceous Research (preprint). doi:https://doi.org/10.1016/j.cretres.2023.105487.

Mo, J., F. Ma, Y. Yu., and X. Xu. 2023 (preprint 2022). A new titanosauriform sauropod with an unusual tail from the Lower Cretaceous of northeastern China. Cretaceous Research 144:article 105449. doi:https://doi.org/10.1016/j.cretres.2022.105449.

Hunting the wild stromatolite at Vermillion Falls

The gorge at Vermillion Falls, as seen before, is cut through quite a bit of the Prairie du Chien Group. Therefore, it is entirely reasonable to suppose that somewhere in all of those oodles of outcrop, there are some stromatolites. It should be just a matter of walking down and having a look, right? We-e-ll, easier said than done. A few factors are pushing against going from "predicted" to "established":

1) The classic booby prize of vertical exposures—sure, there's a lot of surface, but you don't get to see most of it up-close;

1b) Furthermore, for many of the places where you *can* examine the walls, you can't change your vantage point because backing up a foot or two puts you a foot or two lower or in open space (and that never helps). What makes this annoying with stromatolites is they can be expressed in various scales, and what you can't see with your nose on the rocks may be perfectly apparent from a couple of arm's lengths away except for that whole "absence of footing" thing, or a promising feature may disappear as you clamber up the slope to inspect it;

2) The surfaces have been fried to a crisp by weathering, which for our purposes disguises the fine layering and other subtle features.

The existing literature is not especially illustrative. Stauffer and Thiel (1941) included a section taken at the railroad bridge (now a footbridge), which describes the walls as 58.5 ft (17.8 m) of Shakopee Dolomite over 1 ft (0.3 m) of Root Valley Sandstone over 47 ft (14 m) of Oneota Dolomite, with nary a stromatolite mentioned (to be fair, the lithological descriptions are also very slim). The site has made it into a few theses and other student papers (Shea 1960; Squillace 1979; Robins 2005), but that seems to be about it. Maybe this limited documentation is a recognition of the above limitations by wiser heads than mine, but I have the faith of a gambler that something will turn up if I look long enough, so down we go back into the gorge.

Besides, why would I want to sit around inside when I could see things like this?

My strategy involves *not* looking directly for stromatolites, at least not the classic laminated features. I would never see them here except on fresh breaks. Instead, I'm looking for a couple of other features: bedding planes that are undulating rather than horizontal, and anomalously recessive intervals (I've seen elsewhere that stromatolitic intervals may be relatively erosion-prone compared to non-stromatolitic intervals). These two features should be visible even through the stain of weathering that began before the most recent Ice Age.

Down near the falls, in some of the lowest accessible beds, something very promising is apparent.

Left

Center

Right

We've definitely got an undulating surface that is appropriately stromatiform* in appearance, as well as being within an interval that is recessed. (In fact, the interval above is recessed in comparison to the interval above that, so this is not for people who don't like rocks poised above their heads [or, for that matter, people who have a phobia of birds pooping on them, because there are pigeons roosting in cavities above].)

*Google says it can come up with about 328,000 hits for "stromatiform". What it doesn't tell you is how many are useful and how many are just dictionaries, rhyming words, anagrams, pronunciations, and SEO things seeking to boost traffic with lists from dictionaries.

A little closer, between two apparent mounds

So stromatiform...

Obviously the next thing to do is to is to get close and look for finer details. That's where things become less clear. There are, conveniently, some fresh surfaces (not made by me!), and they do show alternating compositions. They are, however, rather thick layers.

Layers in one fresh surface.

Not quite as fresh, but you get the idea.

Layers on a spalled piece, frozen to the underlying moss.

I'd been hoping to find nice stacks of small columns beneath the undulating layers, but they aren't appearing (yet, at least). If we compare to Logan et al. (1964) and May et al. (2012), the latter also dealing with large Prairie du Chien stromatolites, it's as if we've skipped the columnar "Cryptozoon" stage and gone straight to broad "Collenia". This may say something about the local environment, or it may say that I'm just getting excited about some inorganic stromatiform-producing process.

Then there's whatever the heck is this. Bedded sedimentary rocks don't do things like this without a good reason.

If the issue is not immediately apparent, check the annotated version below and click to expand as necessary.

Too bad it was on the other side of the gorge. There's probably a way down somewhere...

References

Logan, B.W., R. Rezak, and R. N. Ginsburg. 1964. Classification and environmental significance of algal stromatolites. The Journal of Geology 72(1):68-83.

May, S. L., L. E. Davis, and D. G. Brown. 2012. Algal stromatolites in the Willow River Member of the Lower Ordovician Shakopee Formation near Chatfield, Minnesota, USA. The Compass: Earth Science Journal of Sigma Gamma Epsilon 84(1, Article 6):42–48.

Robins, C. 2005. The geology of the New Richmond Sandstone. Senior Integrative Exercise. Carleton College, Northfield, Minnesota.

Shea, J. H. 1960. Stratigraphy of the Lower Ordovician New Richmond Sandstone in the Upper Mississippi Valley. Thesis. University of Wisconsin, Madison, Wisconsin.

Squillace, P. J. 1979. The geology of the New Richmond Member of the Shakopee Formation (Lower Ordovician), Upper Mississippi Valley. Thesis. University of Minnesota, Minneapolis, Minnesota.

Stauffer, C. R., and G. A. Thiel. 1941. The Paleozoic and related rocks of southeastern Minnesota. Bulletin 29. Minnesota Geological Survey, St. Paul, Minnesota.