What is this coral with such tiny corallites?

[Pippa]

I found this tiny "pebble" lying at a beach north of Chicago when hunting for interesting non-fossil beach rocks and sea glass. (Yeah, there are people who collect and love sea glass and "just rocks" :-)

 

So now, that I've started to collect coral fossils as well, mostly corals, I've been taking a closer look at some of my old finds and see all sorts of little fossil bits and pieces. This one when I found it, had caught my attention due to the tiny pattern, which I thought at the time was maybe something man-made. (Near a big city, there is a lot of man-made tumbled material to be found at the beaches).  Looking at it with my magnifying glass, I saw that the individual white spots seem to have  the same starlike pattern as the large corals I find. But this thing is almost microscopic.

Is/was there really coral with such tiny corallites? If yes, what is its name? Maybe a tiny favositid?

 

Top:

 

Bottom (and side):

 

  

 

Edited September 14, 2019 by Pippa

[Mark Kmiecik]

I believe you've gotten the ID right. I don't know if it can be ID'd down to species. They are common around the area and all through the Great Lakes region. You should be able to find many more where that one came from. There's some beaches between the Illinois/Wisconsin border and Milwaukee where you can find hundreds in one day. Most will be more water-tumbled than this one and the pattern is less conspicuous when dry, but will show clearly when you wet the specimen.

[Rockwood]

Chaetetid I think.

[Pippa]

5 hours ago, Mark Kmiecik said:

I believe you've gotten the ID right. I don't know if it can be ID'd down to species. They are common around the area and all through the Great Lakes region. You should be able to find many more where that one came from. There's some beaches between the Illinois/Wisconsin border and Milwaukee where you can find hundreds in one day. Most will be more water-tumbled than this one and the pattern is less conspicuous when dry, but will show clearly when you wet the specimen.

Thanks for the tip!

I'll have to venture a bit further north then to do my rock-hounding. I'd love to find a couple of larger pieces just like it. My little pebble's pattern is very clearly visible and nicely defined. Wish me luck!

 

4 hours ago, Rockwood said:

Chaetetid I think.

 

So if I understand the U of Berkeley entry:  https://ucmp.berkeley.edu/porifera/chaetetids.html , about chaetedids correctly, my tiny little find would have been thought to be a part of a tabulate coral until, oops, it was found to have a living relative:  Acanthochaetetes wellsi, a demosponge. So now it is classified as a corallite sponge or demosponge.

Well, I'm all happy for today's Acanthochaetetes wellsi, who now know their ancestry! Hope they're duly grateful to science!   

Thanks so much guys!  

[DPS Ammonite]

7 hours ago, Rockwood said:

Chaetetid I think.

This is not a chaetetid because it has (poorly preserved) radial septae which are not present in chaetetids. The openings are a little large for chaetetids.

 

See: 

https://woostergeologists.scotblogs.wooster.edu/2015/06/05/woosters-fossil-of-the-week-a-chaetetid-demosponge-from-the-upper-carboniferous-of-southern-nevada/

 

 

OP’s fossil magnified fossil bellow.

 

 

 

Chaetetes from KD Fossils. Note lack of septae. 

 

Chaetes do have tabulae and septal spines, short protrusions from the from the wall (in red).

[Pippa]

2 hours ago, DPS Ammonite said:

This is not a chaetetid because it has (poorly preserved) radial septae which are not present in chaetetids. The openings are a little large for chaetetids.

 

See: 

https://woostergeologists.scotblogs.wooster.edu/2015/06/05/woosters-fossil-of-the-week-a-chaetetid-demosponge-from-the-upper-carboniferous-of-southern-nevada/

 

OP’s fossil magnified fossil bellow.

 

 

Thank you DPS Ammonite.

Interesting. I had based my guess that the fossil might be a coral on the presence of a "starlike pattern, which you call more elegantly: radial septae. 

 

Question:  Lake Michigan bedrock in the Chicago area is silurian. The link you provided concerns itself with chaetedids from the upper carboniferous. A quick google search did not give me an answer as to when chaetedids first appeared. Did they even exist during the silurian?

 

So for now, I'm considering the little fossil to be a favositid coral. That is, until somebody posts a convincing reason why it isn't.  

Anyone disagree? 

[DPS Ammonite]

3 minutes ago, Pippa said:

A quick google search did not give me an answer as to when chaetedids first appeared. Did they even exist during the silurian?

The Treatise says that they go back to the middle Ordovician.

[Pippa]

2 minutes ago, DPS Ammonite said:

The Treatise says that they go back to the middle Ordovician.

Aha. So age alone won't exclude them.

But everything you posted, does. 

Thanks. 

[Rockwood]

Okay then we know what it's not.

What is it ?

[Rockwood]

2 hours ago, Pippa said:

Anyone disagree? 

Radial septa developed well enough to be this well, if poorly, preserved ? 

[TqB]

On 15/09/2019 at 7:01 AM, Pippa said:

 

So for now, I'm considering the little fossil to be a favositid coral. That is, until somebody posts a convincing reason why it isn't.  

Anyone disagree? 

I think you're probably right. 

[Pippa]

26 minutes ago, TqB said:

I think you're probably right. 

And as you posted on my other thread:

Quote

I'm not very well up on the less common ones from there but, as you say, it looks like a small corallite favositid, with long septal spines. Something like Astrocerium,, but there are many to choose from and identifying these is usually a bit of a specialist job.

 

Surely looks like you're on the right track.  First googling brings me to this:

https://books.google.com/books?id=Zp5ZAAAAYAAJ&pg=RA1-PA59&lpg=RA1-PA59&dq=Genus+Astrocerium,+under+the+microscope&source=bl&ots=Hc1S61F0Vp&sig=ACfU3U2b1NfXyqSaUOZVyz46lgBGAeYwmg&hl=en&sa=X&ved=2ahUKEwjtoKbA0IXlAhUKnKwKHa07AJgQ6AEwAHoECAgQAQ#v=onepage&q=Genus Astrocerium%2C under the microscope&f=false

 

I feel confident that Astrocerium, even if not exact, is very close.  Good enough for me to label it now.  Thanks so much!