I need an expert opinion on this. Potentially Carboniferous medusae?

[dwallwey]

Recently, while I was doing field work volunteering for the Denver Botanic Gardens in Hoosier Pass, I took time over lunch to look for any potential fossils. What had found was very strange, they looked to be fossils of Essexella and Reticulomedusa as found in Mazon Creek nodules. I believe that the history would make sense for them to be able to be found in Colorado, but I do not know.

Here are my photos, with a penny for scale. 

 

EDIT: I will reply with more photos due to the max filesize

the one here appears to me to be Reticulomedusa, but I need an expert opinion to confirm or deny.

I believe that the reason that they aren't in well-defined exposed nodules like in Mazon Creek is due to the fact that they would open annually due to the freeze-thaw process happening naturally, without having the rest of the surrounding rock mined away.

Edited July 3, 2017 by dwallwey

[dwallwey]

Here is one that really looks like Essexella to me:

Also, the likely reason that the central bump on the Reticulomedusa-looking one is so hard to see is probably due to it being ground against other stones with annual snowfall. These were all found on the side of the mountain like this, exposed.

[izak_]

Welcome!

I'm no expert, but they both look a bit like mineral staining in my opinion.

[FossilDAWG]

I'm sorry to say that I do not think these are fossils, but rather they are mineral stains (probably iron oxide).  Such deposits are common in fine fractures in the rock.  I am not seeing any of the 3-D structure I would expect of a fossil.  Also your rock is extremely coarse-grained (and the first piece looks to be metamorphic, not sedimentary, though it is hard to be sure from a photo) and usually very fine grained rock is needed to preserve soft-bodied forms such as jellyfish.

 

Don

[dwallwey]

Okay. I was wondering, It just seemed too consistent in form of the irony-looking concretions/staining across all of the specimens I found. I was only able to bring home some of the smaller ones.

[dwallwey]

There was what looked to be irony-ish shale or something similar in the vicinity, if that helps. It split apart easily into sheet-like chunks, though I did not see anything like I am finding in whatever this sandstony-schisty looking stone is.

[Miocene_Mason]

1 hour ago, dwallwey said:

There was what looked to be irony-ish shale or something similar in the vicinity, if that helps. It split apart easily into sheet-like chunks, though I did not see anything like I am finding in whatever this sandstony-schisty looking stone is.

Well, if it's "schisty", then fossils are unlikely, and if they are found they are most likely deformed. This is because its metamorphosed, it sounds like quartzite. Shale, however, which is often rich in iron, has a good chance of holding fossils, so keep looking!