Platteville Formation (Ordovician) Hash Plate

[ClearLake]

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

 

[Fossildude19]

Wow!

That plate has it all!!!   

Trilobites, gastropod, brachiopods, bryozoans coral, ostracods! 

Don't think it gets much better than that.

Beautiful plate, and great prep job! Thanks for sharing this with us! 

 

[minnbuckeye]

Looks like you have almost everything the Platteville has to offer all on one hashplate!!!!! I am currently going through a bucket of Platteville fossils collected this summer. So this was a timely post for me!!

[Tidgy's Dad]

Wow.

Quite the hash plate.

I particularly like the ostracods, it's great to see so many different ones and the Eurychilina (if that's what it is) is wonderful.

 

[ClearLake]

11 minutes ago, Tidgy's Dad said:

I particularly like the ostracods, it's great to see so many different ones

Yes, I agree. I think there may be another one or two types in there that I have to explore a bit more. Unfortunately, when they are firmly in the matrix like most of these are it is hard to see some of the diagnostic features. But they are great looking. 

[Tidgy's Dad]

22 minutes ago, ClearLake said:

Yes, I agree. I think there may be another one or two types in there that I have to explore a bit more. Unfortunately, when they are firmly in the matrix like most of these are it is hard to see some of the diagnostic features. But they are great looking. 

May I also say that I love it when people pay attention to all the beasties in a piece and include the bryozoans, ostracods and such.

Many just go for the trilobites and brachiopods.

[Tetradium]

Very nice collection. Other than the fact that I can't find any information that tell the difference from S. billingsi from S. plattinensis. The sources also listed a different species of Hesperorthis from the Platteville Formation too. 

[ClearLake]

2 hours ago, Tetradium said:

Other than the fact that I can't find any information that tell the difference from S. billingsi from S. plattinensis.

All I can offer to help at the moment is this excerpt from MGS RI35 page 57:

 

Discussion
Strophomena billingsi? can be distinguished from other members of this
genus by its small size. low convexity, delicate shell, prominent. coarse. radially
disposed pseudopunctae (though not nearly so coarse as in
Rafinesqllina. in which the pseudopunctae are not radially continguous) and
a pedicle muscle field not enclosed laterally or anteriorly by muscle-bounding
ridges. Visceral marks of any kind are much more faint in this species
than in any other species of StroplwmenG in this collection.
Caution in assigning this name to the specimens is warranted because the
type specimen is lost (UMPC 8192) and is not figured by Winchell and
Schuchert, who only reproduce the rather inconclusive figures of Billings
(1865, fig. 108). In addition. the specimens in this collection are more alate
than the figured specimen.

[ClearLake]

2 hours ago, Tetradium said:

The sources also listed a different species of Hesperorthis from the Platteville Formation too.

 

 

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

Edited December 30, 2023 by ClearLake

[FossilDAWG]

That is an amazingly diverse hash plate!

one small suggestion, I think the “small horn coral” may be a Cornulites, a type of tube worm with a calcareous tube.  These always grew attached to some kind of a hard substrate, commonly a shell.

 

Don

[ClearLake]

1 hour ago, FossilDAWG said:

one small suggestion, I think the “small horn coral” may be a Cornulites

Interesting idea.  I had considered Tentaculites but ruled it out due to more irregular "rings" on this specimen and its non-straight nature, but I'm not sure I really considered Cornulites.  I went and dug out my two other specimens of Ordovician Cornulites that I have cataloged for comparison (they are from the Cincinnati area).  Both of those examples have more regular and defined rings than this specimen, but a lot of Cornulites I see online look pretty similar to this example.  I went and cleared a bit more matrix from the opening end to see if I could see septae - none are obvious.    I looked at the Cornulites examples from the Feild Museum website and they all have very regular rings (in fact several look just like Tentaculites to me???).  I read in a couple of places that the rings on Cornulites get more regular on adult specimens, so maybe mine is just a teenager.

 

As I look at more examples, I think you may be right, Cornulites could be a better ID.  Thanks!!!

[Tetradium]

Thanks. Just keep in mind to read Molluscan and  Brachiopod dominated biofacies in the PlatteviUe Formation (Middle Ordovician), upper Mississippi Valley.

 

It also points out how the different locations have very widely varied communities in which certain species predominates.  For example, Wisconsin have much more Campyorthis and Hormotroma gracilis which is rarer in Twin Cities region at least in Platteville Formation.

Twin Cities region is very Oepikina minnesotensis and Strophomena dominated.