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Hi there @mark-ryan You can update the Geochron to Eon: Phanerozoic Era: Paleozoic Period: Ordovician. Based on this group’s fossils, this looks like it may indeed be an Ordovician sponge. Here are some resources for further ID research: http://www.fossilspot.com/STATES/MN.HTM http://www.ordovicianatlas.org/atlas/bryozoa/stenolaemata/trepostomatida/monticuliporidae/prasopora/

@jbauer any ideas on this one? Seems interesting.

Hi @mark-ryan & @vperez – this is a weird one. I am not sure about stromatoporoid, those are calcified so I would expect better preservation. It’s possible that the circular bit on the ‘bottom’ is a nucleation point for a sponge or something trying to anchor down – so it could be an unrelated animal piece. That star shaped pattern on top is also weird – I’m not sure what it is though? It could be the opening of a sponge. It’s interesting how many you have found over the years and in a localized area.

The Paleozoic sponge that comes to mind is Hindia but that usually is pretty round and has less features so I’m pretty stumped!

Have you seen this blog: https://equatorialminnesota.blogspot.com/ maybe there will be some clues?

Hi @jbauer – Thanks for your comment. Yes, it’s a very weird fossil. I’m mainly stabbing in the dark about these things but it’s been fun doing so. If it is stromatoporoid, the strange star-shaped feature (astrorhizae?), may be part of it or another creature entirely. I don’t think the circular stalk is unrelated to the “mushroom cap” because in this particular specimen the stem is much shorter than those seen in others I have. Since I could only post a single specimen I used this one because it showed the most detail on the cap (top). Some of the others I’ve collected have longer, more distinct stems. I should add that I also find in the same small area longer segments of similar stems/stalks (with no “mushroom caps”) that might be associated with the caps. I thought initially they were just pieces of bryozoa or the eroded internal structures of bryozoa, but have since noticed how very similar they are to the “mushroom cap” stalks; they have a smooth surface and contain no pores like bryozoa do, and their diameter matches very nearly the diameter of the cap stalks. I should point out also that some of the “mushroom cap” specimens display additional contact points where stalks could have possibly attached indicating maybe some sort of connected lattice or maybe flowering structure containing several “mushroom caps”. Just a thought. The broken stalks have also been a good indicator that “mushrooms caps” could be nearby and that has usually been the case. However, I recently followed the exposure to another site on the other side of the hill and found two of these stalks but no “mushroom caps”. I need to further explore that site. Regarding the Equatorial Minnesota blog: its author, Justin Tweet, is aware of these fossils as he and I both volunteer as preparators in the paleontology lab at the Science Museum of Minnesota and have had discussions about them. Right now, one of the “mushroom caps” and a couple of individual stalks are being prepared for examination under an SEM and other analyses. I should know more within a few weeks. Thanks again!

@mark-ryan – this is very interesting. It’s so fun to speculate!!! Especially when everything is so unknown. It’s certainly a possibility that the single star shaped feature is an astrorhizae – but I’ve never only seen one have you? Usually it’s a whole mess across a surface, usually associated with monticules – but these are usuals, there are certainly unusuals as well!!

Good to know about the weird stem – it was hard to tell if it was related or not from the images. It certainly could be. RE- bryozoan – do you see any zooecia? Is the structure calcified? It looks like a sediment mold to me but – hard to tell from images. Can you tell me how you find these in the field? Is it mushroom cap up with the stalk down? Are they loose?

That’s great to know you are working with the Science Museum of Minnesota!! I am really interested in this – let me know what you all find. Do they have X-ray equipment there? Even a flat bed to see if there are changes in material would be really cool. If not let me know – we (UMich Paleo) are still working on getting all of our equipment up and running after being shut down but I’m happy to try to get one scanned for you.

Talk soon,
Jen

@jbauer – Hi Jennifer. I’ve posted several photos of these strange things on my Flickr page which can be viewed here: https://www.flickr.com/photos/rynoceras/albums/72157662532368937
You’ll see a mish-mash of several shots of different specimens which should give you more visual information than my single post here. I get out to Cannon Falls a couple times each month especially after heavy rains which we seem to be getting a lot of lately. I was last out on August 14th and found two more specimens along with many possibly associated stalks – again within the same 1.5 meter square area. You’ll note field photos of the “mushrooms” in situ. The larger specimen is interesting in that the “cap” does not totally enclose the stem. I have one or two other specimens that appear the same way. Maybe these things attach themselves to the end branches of bryozoa (or something) for whatever reason and grow around it. As far as I can tell, none of the stems attached to the “mushrooms” ever show any signs of zooecia. The loose stalks and bryozoa branches looks very similar in the field. All the stalk material I bring home I wash and check out under magnification and sort the “stalks” out from bryozoa branches which have the obvious zooecia. The stalks could definitely be sediment cores of bryozoa. That’s what I first thought – I usually just passed them over because bryozoa is so common in the Decorah. But since they seem very similar in shape, texture, and color to the “mushroom” stems I started to pay more attention to them. I’m not sure what they are now. Or if they’re even related to the “mushrooms”. Near the end of the Flickr album I included a couple iPhone photos my university friend sent to me showing set-up for grinding/polishing/analysis of a “mushroom cap” specimen and a couple stalks. He told me he’d finish them up after he gets back from Montana. I haven’t heard back from him yet but I expect to soon. In the cross-section he sent it looks like the stalk’s interior shows mostly sediment with a little crystallization. There’s also the tiny black shapes (oolites?) present which often appear on the exterior of the stalks and the “mushroom caps” (and on other types of fossils). They look like tiny charcoal briquettes, especially under the microscope. I’ve added a couple so-so close-ups taken with my iPhone through my microscope eyepiece at the end of the Flickr album. I may be incorrect in referring to them as oolites but they’re probably some sediment feature (fossils found down the road contain “brassy oolites” – maybe these are just oxidized ones). One last thing – note the additional “attachment/extension” protuberance seen on some of the “mushroom cap” surfaces. I wonder about those, too. Do these suggest interconnection between caps? More food for thought. Anyway, I hope this gives you a better idea of what these things look like. Thanks for your interest in all this and also for your offer to help analyze these odd little things. SMM doesn’t have an X-ray machine at this time but my pal at a local universities has access to some great analysis equipment including an SEM and as I mentioned will complete the job when he returns. I’ll will definitely bring you up to date on any new developments. Let me know if there’s a problem accessing the Flickr link. Thanks again!