Unknown Michigan Fossil - Coral??

[Sinosauropteryx prima]

Hello everyone, back again with another request for fossil ID.

 

I found this rock on a small rocky beach in western Michigan, the same location I find a lot of my fossils in. At first glance I thought it may have been a Petoskey stone (Hexagonaria percarinata), but upon closer examination it doesn't really look anything like one. In fact, it doesn't really even look like a coral to me, though I could be wrong. That is my only guess, so it might actually be one. I'm also curious as to the reddish bands that are visible on the side of the rock. If anyone could shed some light, it'd be greatly appreciated.

 

Thanks!

[Darbi]

51 minutes ago, Sinosauropteryx prima said:

Yes, I think it is Petoskey stone. Notice the "gill" structures in each hole and also it have 5 to 6 sides.

[TqB]

It's certainly a colonial rugose coral but it's not Hexagonaria. I think it's Arachnophyllum or related arachnophyllid, quite a lot rarer in that area and a good find.

The bands on the side are its normal structure in vertical section (see the section below).

 

(Be aware that the majority of "Arachnophyllum" images on Google search are mislabelled corals from Morocco!)

 

Here's a Silurian one from the UK.

 

Horizontal and vertical sections:

[Sinosauropteryx prima]

7 hours ago, TqB said:

It's certainly a colonial rugose coral but it's not Hexagonaria (the Petoskey Stone genus). I think it's Arachnophyllum or related arachnophyllid, quite a lot rarer in that area and a good find.

The bands on the side are its normal structure in vertical section (see the section below).

 

(Be aware that the majority of "Arachnophyllum" images on Google search are mislabelled corals from Morocco!)

 

Here's a Silurian one from the UK.

 

Horizontal and vertical sections:

Wow, sure looks like it! Thanks a bunch!

[Darbi]

16 hours ago, TqB said:

It's certainly a colonial rugose coral but it's not Hexagonaria. I think it's Arachnophyllum or related arachnophyllid, quite a lot rarer in that area and a good find.

The bands on the side are its normal structure in vertical section (see the section below).

Well, never heard of these corals until now. Looks like I need to learn how tell the differences between Hexagonaria and arachnophyllid!

[Sinosauropteryx prima]

1 hour ago, Darbi said:

Well, never heard of these corals until now. Looks like I need to learn how tell the differences between Hexagonaria and arachnophyllid!

I'd never heard of them either. It's so interesting to learn about all these other species. 

[Pippa]

Very cool find!

That's the second Lake Michigan Arachnophyllum thread on this forum in two days.  Amazing!  I believe these things are pretty rare in Lake Michigan, especially when compared to hexagonaria or favosites.

 

I hadn't ever heard of Arachnophyllum before posting an ID thread of what I thought was a solitary rugose coral  back in February. TqB suggested it might be an Aphroidal Arachnophyllum or similarr - a colonial Rugose coral.

Then, just a couple of days ago, I googled Silurian colonial corals to research a more recent find and stumbled upon a USGS survey report that describes various members of the Arachnophyllum genus. So I posted an ID thread of this new find, to receive some opinions on it. TqB confirmed it to be either an Archnophyllum or very similar genus.  Since then, I've done some more googling on its proven occurrence in Lake Michigan, and yes, it is listed as being found in the Devonian rock in the Michigan basin. See here:  https://www.michigan.gov/documents/deq/GIMDL-PA03_216189_7.pdf 

 

Hope the links will be helpful to you, as it appears to me that the members of the genus Arachnophyllym vary hugely in their growth habit and appearance. Surely, I never guessed that my two disparate colonial Rugose corals are cousins of a sort, members of the same genus.

 

Good luck, and happy hunting!