Silurian Demosponge or Sponge?

[Pippa]

Hello,  

I'd appreciate your help with this one. 

I found  this one at a Lake Michigan beach in Illinois. Silurian from the Racine formation. 

I believe it's a sponge or demosponge. Thinking the white dots on the vertical growth are pores, and the admittedly terrible microscopic photo of a small area on top of the rock shows some of its openings. Some of these seem to be filled with minerals that make them look like bumps, many others aren't preserved well at all, just show as faded round dots.

Am I way off on this? 

TIA, Pippa

 

 

 

 

[ClearLake]

To me it looks more like splintered/ shattered brachiopod shell. Perhaps one with a punctate shell to account for all the small pores. Those “vertical” striations look like costae on a shell. Unless it is a lot thicker than I am imagining it from your picture. Just a thought.   Perhaps Adam will have an idea @Tidgy's Dad

[Pippa]

ClearLake,

 

Thank you for your response.

Well, that's what my first thought when I found it. Thing is, the ribbing is microscopic, barely visible by eye, much, much tinier then on any of the brachs I've found so far. 

The other thing is, that only a small part of this thing is visible on the surface. Small areas of ribbing are found in areas all around the quite large rock and the top is covered with dots and "openings" that look to be tubes, like the trio on the third photo. That made me think sponge of some sort.

Also, I've not seen a brach from Lake Michigan fossilized this way. Even fragments are usually quite well preserved.

But then, what do I know, I am a rank amateur, there is much that I donot know and haven't seen. 

 

I appreciate you calling Tidgy's Dad. I was trying to call DPS Ammonite and TqB, who have been a great help to me with my finds. but I have forgotten how to do so....  

Gotta go back to work...

[Tidgy's Dad]

I agree with Mike, it's part of a brachiopod shell showing punctae / pseudopunctae. 

Probably a strophomenate. 

[Pippa]

1 hour ago, Tidgy's Dad said:

I agree with Mike, it's part of a brachiopod shell showing punctae / pseudopunctae. 

Probably a strophomenate. 

 

Shoulda gone with my first thought then. :-)

Thank you both so much for clearing that up and Adam, I really appreciate the proper term for the "dots". That's so helpful. 

Stay safe!