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Brachiopods of Platteville/Decorah Twin Cities Minnesota
Images added to a gallery album owned by Tetradium in Brachiopods
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During our last warm spell in November ( a high of 40 may not sound warm to you southerners), I took the opportunity to collect a few buckets of Decorah Shale to process during the cold snowy month of December. Here are some of the fossils found. Nothing too exciting, but fun to find!! @Tidgy's Dad, I would be pleased if you could assist me with my attempted IDs!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! And if there are some that you do not have yet, let me know and I will see about sending. 1. I suspect Platystrophia extensa 2. Sowerbella minnesotensis. pedal valve above convex, brachial valve below concave 3. Sowerbella curdsvillensis. 4. 5. Rostricellula colei has far less costae than the one above and the costae are broad and smooth. 6. Pycnocrinus are prevalent in the Decorah, but mostly small partial stem pieces 7. Endoceras are the most common cephalopod I encounter in this formation, so the Isorthoceras was a welcome find. 8. Interior pedal valve of Strophomena filitexta, showing the well developed ridges for the large muscle attachment. 9. Unknown Strophomena interior pedal valves? At 2 cm wide and lacking the ridges of S filitexta, I am guessing Furcitella scofieldi. 10. The gumdrop bryozoan, Prasapora conoidea, has always been an enjoyment to find. They come in many sizes and shapes. The next one has me a bit confused. Normally Prasapora are NOT attached to anything and show the obvious growth rings underneath. This one obviously is attached to a Strophomena leading me to wonder if it is a sponge or another species of bryozoa instead. Thoughts are welcome. 11. The Decorah Formation yields many Hesperorthis tricenaria. The pedal valve is easy to identify with its beak and its triangular delthyrium. It is the brachial valve that I am not sure of. This is my guess to its identity. Very flat with similar ribbing to the pedal valve Here is a sample that contains what I think are both pedal and brachial valves 12. The solitary rugosa coral, L. profundum, is found every time I hunt the Decorah. Here is a nice specimen in association with a few Sowerbella. But this particular hunt provided me with two unknowns. First, is this a colonial rugosa or just 2 solitary L. profundums side by side. If colonial, I can not find any mention of a species name. The second odd coral is this one. Very small and appears worn even though the matrix it popped out of was not 13. Many species of branching bryozoa are commonly found both loose and in matrix. 14. Pionodema subaequata at the top and Doleroides pervetus below. 15. These two are 3cm by 2 cm, leaving me to think an interior and an exterior surface of a brachial valve of Strophomena septa. The size of this one is 2 cm by 1.5 cm. This pedal valve is quite raised, so I am suspicious it is Oepikina minnesotensis. 16. A possible pedicle valve of Pionodema subequata. 2 cm by 2 cm 16. 17. Brachial valve interiors of Sowerbyella curdsvillensis 18. Inarticulate brachiopods, Lingula. It is difficult to find a pristine one at the site I hunt. But I will keep trying! The name has changed to Pachyglossella eldei. 20. Gastropods are infrequently encountered in the Decorah, yet above and below this formation, they are common.
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- decorah shale
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Magnanimous Mike @minnbuckeye has kindly sent me some more specimens from the Decorah Shale Formation from Decorah, Iowa. I've been missing the many wondrous and beautiful, free-from-matrix bryozoans so far in my Devonian collection, so it's nice to dip back into the Ordovician and enjoy this beautiful specimen of Prasopora conoidea. A couple of bits of other bryozoa stuck to the underside. The one on the right could be Graptodictya, but there's not enough of it to be certain. It's also quite nice to compare and contrast it with the Decorah Prasopora simulatrix which is more domed than conical: See the top of page 9 of this thread for more photos of P. simulatrix from the Decorah Shale and two-thirds of the way down page 27 for P. simulatrix from the Verulam Formation of the James Dick Cement Quarry in Ontario, Canada.
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Oklahoma 3 So far on my excursions around Oklahoma I have been greeted by goats and elk. The start of day 3 had me face to face with something I hadn’t anticipated! And it wasn’t another Oklahoma gate. No, it was a dazzle (what a herd of Zebras are termed) from the genus Equus. As I exited my vehicle, this particular Zebra was snorting. Thank goodness when Zebras snort, it is a sign of contentment. Zebras also stretch their necks out and put their ears forward when inquisitive. So this guy obviously wanted to greet me in a friendly way! So, a question for everyone reading this post. Are zebras white with black stripes or black with white stripes? This topic was discussed during a class on Zoo Veterinary Medicine years ago. The answer is at the end of this post. The owner of the quarry was on vacation, so it was just my striped friends and I enjoying the beautiful morning. Here is a photo of the site. My sledge had a good workout but unfortunately, little was exposed. This was all of my finds after 2 hours of collecting and most were already exposed. A suggestion given to me indicates this was the Ordovician, Bromide Formation. Since I do not know the formation for sure, identification has not been given to the fossils. #5 is very odd. I am not sure if it is a fossil or a mineral. Opinions welcomed! An opinion as to whether 6. is a bryozoan or a crinoid holdfast would be welcomed! 11. Initially, I assumed that this was a bryozoan or coral. But after cleaning it up and looking closer, I am wondering if this is a Floating Crinoid Bulb??? It was a specimen I hoped to find. The afternoon was to be spent exploring the Ordovician's Viola Formation. On the way, I photographed a typical scene of the area and of coarse, some more wildlife. The rains this past week with the resulting mud continued to make hunting difficult. But results from the Viola Formation pleased me. The brachiopods need a bit more prepping though. 1. Star shaped plates from the crinoid Colpodecrinus and a plate from a Rhombiferan cystoid 2. 3. 4. 5. This reminds me of Prasapora of the Decorah Shale but did not find Prasapora mentioned in the Viola Formation 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. Calyptaulax strasburgensis cephalon and Bumastoides billingsi pygidium. Hope everyone has enjoyed my trip reports. There may be one more after identifying my finds. a. So now to answer what color is a Zebra. Black! Black is color of a zebra. Beneath all that fur, zebras have black skin. Even under the white stripes!
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This is a lovely chunk of the nautiloid Endoceras proteiforme also from the Decorah Shale in Iowa. The shell itself is gone so this specimen is composed of the internal casts of the individual camerae and as the septa are gone, the specimen likes to fall apart. It had been reglued a couple of times by Mike and then I had to glue a couple of bits back on after it had been through the postal service, but no real harm was done. I think the siphuncle in the picture below? Ventral from the centre but not at the margin would fit. @minnbuckeye Mike, thank you so much once again for expanding my Decorah Shale and Ordovician of the USA collection, it is very much appreciated.
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February 2024 Invertebrate / Plant Fossil Of The Month Poll
digit posted a topic in Fossil of the Month
Check the entries below carefully and cast your vote! PM me if you notice any errors with the entries. The poll ends March 9th. Be sure to vote in our other FOTM poll, HERE 1. Eomonorachus intermedius trilobite (ventral view) - Ordovician, Decorah Formation - Missouri 2. Orthoconic nautiloid - . Carboniferous, Malahide Formation - Dublin, Ireland 3. Lioplacodes tenuicarinata gastropod - Late Cretaceous, Maastrichtian, Hell Creek Formation - Garfield County, Montana 4. Triarthrus eatoni (trilobite), Sanctacarididae indet. (raptoral appendage), graptolite - Ordovician, Beecher's Trilobite Bed - Rome, New York 5. Tropaeum bowerbanki heteromorph ammonite - Cretaceous, Lower Crioceras Beds - Whale chine, Isle of Wight, UK 6. Placenticeras pseudoplacenta ammonite - Upper Cretaceous (Turonian), Carlile Shale - New Mexico
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Hello, everyone; This is a hash plate from the lower Decorah Shale of St. Paul, Minnesota. The central item in the photos is a thin dark fossil with crenulated segments. It appears that the fossil forms a nearly complete perimeter, defining a cross-section that seems to be uninterrupted on the side in the block but pinched into a bilobe on the side facing away from the block (either natural or crushed into that shape from a cylindrical or oval cross-section). Where the lobes pinch there is what appears to be a sediment-filled longitudinal gap. The scale bar has colored alternating millimeters, so we're looking at something a few millimeters across. My immediate thought was that this is phosphatic, as it is preserved similarly to trilobite fragments in the same plate (and in the Decorah in general). I can rule out most of the common groups immediately based on the apparent composition and general shape (sponges, corals, bryozoans, brachiopods, mollusks, and echinoderms). Because of the similarity to trilobite preservation, I first thought arthropod, but it certainly doesn't appear to be trilobitic. Obviously it's not an ostracode. I have very little experience with eurypterids but it doesn't seem like them, either. The other thing I've been considering is a machaeridian worm fragment, which would explain the apparent longitudinal gap and bilobed cross-section, but that crenulation thing is curious. Would any of you have any thoughts on this object?
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Minnesota Ordovician Decorah Cephalopods
Images added to a gallery album owned by Tetradium in Member Collections
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Seem to be two different group (I'm talking about the larger shells not Sowerbyella minnesotensis) but I'm not sure. Top rows appear to have wave like ripples described as Bellimurina charlottae. From Southeast Minnesota in solid beds of limestones associated with Decorah Formation. I wish I have one showing inside of shell hinges.
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From the album: Brachiopods of Platteville/Decorah Twin Cities Minnesota
Very recently in 2023 paper came out that basically places all Zygospira earlier than Mayville/Richmondian in genus Anazyga. Cinnicinntea website also had name change for Anazyga recurvirostis since it also extends into maysville formation. The Decorah Formation Twin Cities can have a lot of those but oddly enough to me they are very specific to muddy limestone as I never find them in the weaker shales for unknown reasons. One of the tiniest Decorah Formation Brachiopod species I have ever found, tiny enough to balance on eraser end of pencil. Compare to the other Anazyga species it is much smaller and more inflated in shape. -
Hi, Mike, I have just been enjoying the lovely chunk of Endoceras proteiforme that you sent me and have been looking at the other nautiloids found in the Decorah. I think that the species of Isorthoceras that you have here is not I. sociale, which can be found in abundance in Graf, Iowa and elsewhere, but Isorthoceras junceum. Nice find.
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February 2024 - Finds of the Month Entries
Collector9658 replied to digit's topic in Fossil of the Month
I'll take a stab at it. I took a short reconnaissance trip on the first of the month that paid off! This weathered, but complete ventral Eomonorachus intermedius trilobite is the largest speicmen I found that day, measuring in at 1.4cm in length. • Date of Discovery: February 1, 2024 • Preparation Completion Date: February 1, 2024 (As found) • Scientific and/or Common Name: Eomonorachus intermedius (ventral view) • Geologic Formation and/or Geologic Age: Decorah Formation, Ordovician • State, Province, or Region Found: Missouri
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Thank you. Yes, I think there are several species, especially near the top of the formation, but I need to do more reading. Here is the wonderful obolid lingulid Pachyglossella elderi ( was Lingula elderi). I think it interesting that Lingula is "little tongue" in Latin, from "lingua" -"the tongue" which can mean the body part or the language and is the root of words such as linguistics, language, etc, while glossa is the Greek for the same thing and gives us the word glossary, for example. So Pachyglossella means "thick little tongue". Pachyglossa was already taken by a modern plant. My first inarticulate brachiopod from the Decorah shale and my first specimen from its subfamily; Glossellinae.
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Seems likely, especially if these are Decorah rocks.
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Very informative! I did not realize there were 3 species of Prasapora in the Decorah.
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Hunting spots unfortunately come and go. And so it will be with the site I visited this week having been one of my favorite local spot for Decorah Shale fossils it saddened me to see construction taking it away from me. So I hunted it hard and it produced fairly well. First up are a few hash plates. There was a discussion this week on whether fossils should be left in matrix or not. I decided to provide a little of both There seems to be two types of rugosa coral. One is very smooth. The other has rough ridges. The only species name I have for the Decorah is Lambeophyllum profunum, which I feel is the smooth one. I found dozens of Strophomena but have a difficult time differentiating the various species based on the look of one side of one shell. So I didn't bore you with many pictures of this genus. These are worm burrows, very common in the Decorah. I find these on occation and call them sponges. It is a ball with a stalk that seems to have attached to something. Maybe it is just a common Prasapora bryozoan. This was one of my favorite finds of the day. Gastropods in the Decorah are not pretty. The Platteville below and the Galena above produce many nice gastropods. If anyone knows an explanation, I would love to hear it!! This is your typical Prasapora bryozoan of the Decorah. Two species are mentioned without a description of how to tell them apart. This next species of Prasapora is easy to tell apart. But is uncommon to find. I was ecstatic to grab two in the same trip!! This picture speaks of how easy it is to ID a P. grandis from the others!! Now I must tearfully say goodbye to this site. But construction continues to boom in the area and new exposures will likely show up. Mike
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A brilliant mailbox score for me This was sent to me by the totally wonderful Mike @minnbuckeye My favourite period - Ordovician, My favourite epoch - Wenlock My favourites phylum - brachiopods My favourite genus - Leptaena. A range of phyla beyond the brachiopods. This is the perfect gift for me. The top lot is a wonderful selection of unprepped Cerro Gordo Late Devonian stuff and the top right few are additions to my Decorah collection. The others are an amazing amount of specimens to add to my blooming Waldron Shale collection. What more could one want? I cried a lot going through these. Thanks, Mike, it means so much in so many different ways. Edited just now by Tidgy's Dad
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Well, here is what I opened as my Eastern Orthodox Christmas present. This was sent to me by the totally wonderful Mike @minnbuckeye My favourite period - Ordovician, My favourite epoch - Wenlock My favourites phylum - brachiopods My favourite genus - Leptaena. A range of phyla beyond the brachiopods. This is the perfect gift for me. The top lot is a wonderful selection of unprepped Cerro Gordo Late Devonian stuff and the top right few are additions to my Decorah collection. The others are an amazing amount of specimens to add to my blooming Waldron Shale collection. Love you, Mike! Some of these brought tears to my eyes,
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In my Secret Santa gift last Christmas from @connorp I received (among other nice items) a very nice little hash plate from the Mifflin Member of the Platteville Formation (U/M Ordovician, Blackriverian, ~453 MY) from SW Wisconsin. The picture below is the plate as it was received and in my 12/20/22 post about getting it I said: “A great hash plate. I already see two or maybe three different trilobite types with a couple of them tantalizingly partially buried and an interesting gastropod that I am not familiar with. I think a little prep work will make this even more spectacular. As an added plus, it represents my first fossils from the state of Wisconsin.” I finally got around to doing the prep I talked about and spent a little time exposing some of the more prominent fossils and giving it a gentle going over with air abrasion to bring out some of the features. I think it looks even better than it already did and I was even more impressed with the wide variety of fossils on the small section of rock. Below is the cleaned up plate: Here is a collage of the plate just turned at different angles to the sunlight in case it helps to bring out any features: There are hundreds of fossil fragments on this one small piece of rock, but I want to highlight the top couple dozen specimens. With the help of some TFF members via previous posts and replies in a couple of ID threads I put out (thanks @Tidgy's Dad, @connorp, @piranha, @minnbuckeye and others), I have identified several trilobites, brachiopods, gastropods, ostracods, bryozoans, and a crinoid and want to show you this wonderful diversity in such a small space. If anyone sees changes to my ID's please feel free to chime in. Some will be very specific ID's and some will be a bit more general. The picture below is the key to where each of the numbered specimens is on the slab (see number in upper left of each specific picture). We will start with the trilobites. Although each is only a partial, there is enough present to get a pretty specific ID on most of them. All are new genera or species in my collection. Here are the brachiopods: Here are a couple of specimens of a really neat gastropod which was new to me. So often it seems Paleozoic gastropods are just internal molds or rather plain forms, but this first one is very nice. Here are a few bryozoans and one very small horn coral. There were several of these small corals, I'm not really sure of the ID, I didn't research them much yet. Just a couple of small crinoid columnals were found. And last but not least are the ostracods. I am used to small ostracods (which some of these are) but there is also this one form that is huge (by ostracod standards) coming in at about a centimeter long. At first I thought they were brachiopod fragments until I looked at them closer. These things are the size of a kidney bean! Note the scale difference between the Eoleperditia and all the others. Most of my ID's are questionable as I was using a reference that is for the immediately overlying Decorah Formation until I can find a listing for the Mifflin Member. OK that is everything for now. I hope you have enjoyed the wonderful diversity of this small slice in time. With a little more investigation, I may yet tease out a few more specimens worthy of an ID. Thanks for looking. Mike
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I saw the checklist out of MGS RI-35 for the Platteville Fm and noted that it does list a different species, but then on page 131 there is this passage (see below, bold is my addition). I forget which source I used on the difference between the species, but the strong central ridge on the interior of this valve led me to H. tricenaria. I will have to research a bit more on the differences between H. tricenaria and H. concava. Thanks for the thoughts! BRACHIOPODS AND TRILOBITES OF THE PLATTEVILLE AND DECORAH FORMATIONS The lowest stratum included in Sardeson' s bed system is the Glenwood Formation. It is almost entirely devoid of macrofossils and, in generaL it is not worthwhile hunting in the Glenwood. Also included in Sardeson's bed 1 are the Pecatonica and Mifflin Members of the Platteville Formation. The Pecatonica is poorly fossiliferous but the Mifflin contains a fair number offossils. However, collecting in situ Mifflin can be tedious and umewarding because the Mifflin is a cliff-former and the fossils are best exposed on the bedding surfaces. In over 40 years of collecting, Sardeson was able to find hundreds of easily extractable fossils in the shaly partings, but it is probably easiest to collect slabs of the distinctively crinkly-bedded Mifflin in the talus at the foot of the cliff. Common Mifflin brachiopods include Campylorthis deflecta, Oepikina minnesotensis, Hesperorthis tricenaria, and Rostricellula minnesotensis, while [sotelus simplex, BlImastoides milleri, I1laenlls sp. , and various ceraurids make up the bulk of the trilobite fauna. The Hidden Falls and Magnolia Members of
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From the album: Brachiopods of Platteville/Decorah Twin Cities Minnesota
Those are the closest specimen I could find that I think is Anazyga lebanonensis. Described as longer in length than the other two Anazyga species from Decorah Formation. -
From the album: Brachiopods of Platteville/Decorah Twin Cities Minnesota
Lepidocyclus - Decorah Formation only? For me I hadn't found it in Platteville formation for unknown reason - could be locations. Very abundant and highly variable in forms - I suspects quite a few genus and species can be easily mistaken for this one. Part of it is I only find the smallest ones as strongly triangular and more flat with sulcus not as prominent. But all the bigger one are much more inflated. Plus costae is pretty uniform over all species. Transverse growths are sometimes prominent on anterior portion of the shell, usually on adult specimens. -
Sara: The World Traveling Ceratopsian
Caverat replied to caldigger's topic in Member-to-Member Fossil Trades
Today we got to a half shelf and explored some of the top shelf specimens. First up was a slab with Middle Ordovician Hormotoma gracilis from the Decorah or Plattin Group of Jefferson county, Missouri. I've micro-engraved around the gastropods to expose them more, but need an airbrasive unit to do more cleaning! Next, Sara sat on a specimen with the cephalon of a Raymondites ingalli from the same formation and location. Sure wish I'd found a complete one instead of the cephalon only... (pictured). Next up is a favorite, not the many Rafinesquina brachiopods, but the cluster of Cornulites corrugatus "worms" all attached on one brach and oriented toward the brach's mouth to catch the current and food! I haven't been able to identify the rounded mass attached to the nearby brach - possibly a sponge? Help! Sara looked at this elongated gastropod and she couldn't help me identify it either... All of these specimens came from the same locality and the same day, for that matter. So this gastropod is Middle Ordovician and the Decorah or Plattin Group.
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First trip of the year to Decorah Shale Formation in Ordovician Minnesota. This was one of the few fossils I found - I assumed it was a regular Large Gumdrop Bryozoan, Prasopora conoidea. Then when I got to cleaning the clay and soft shale off it looks so different. No noticeable pores and sharp angles. Here's two Large Prasopora conoidea - one smooth form and one rough and layered form on the left side for comparation. There is also a little Hormotoma fragilis gastropod on top. It doesn't even look like a trace fossil, as trace fossils are usually harder than usual shale or gathering of coarse sediments.
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Yes, thank you that is a good one that I have looked at. Unfortunately both articles deal with the Decorah and not are not inclusive of the Mifflin, but it certainly gives me a good head start on families and genera. Thanks!
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