Mystery fossil discs

[nivek1969]

Hello again. I have several of these strange fossil discs. I cannot find tags for them in the boxes of minerals and fossils recently acquired. Possibly some sort of jellyfish? sea sponge? Any help with ID is of course always appreciated!

 

[nivek1969]

coral maybe?

[grandpa]

I'm thinking a "button" coral.  Do you know the age?

[MightyPretzel]

Reminds me of an oncolite.

[nivek1969]

5 minutes ago, grandpa said:

I'm thinking a "button" coral.  Do you know the age?

I do not. These were in a packet with no ID cards, unfortunately. The bottom side looks like the bottom of mushroom caps! ha! They are intriguing. 

[nivek1969]

I have about 6 of them, strange they are all like prehistoric "coins" in the fact that they are all a similar size with the same concentric circles on top. 

[BobWill]

Could these be intervertebral discs?

[nivek1969]

15 minutes ago, BobWill said:

Could these be intervertebral discs?

I don't think so, the concentric circles are more pronounced than with a intervertabral disc, I think. I'm thinking a type of sea sponge/echinoderm. They also sort of resemble algae stromotolites, but not quite right being discs free from a matrix with front and back impressions. 

[nivek1969]

1 hour ago, grandpa said:

I'm thinking a "button" coral.  Do you know the age?

I am thinking you are correct. Thanks for the info! 

[grandpa]

See for example:

 

https://www.sciencephoto.com/media/171470/view

 

Note both the concentric growth ring pattern and the radial pattern in the photo and in your specimen.  This says "coral" to me.  Unfortunately, I can't help with genus and species, but someone will surely come through with this info. soon.  Too bad you don't know the age.  That would help in narrowing it down.
BTW, I could be totally off, you know.

[nivek1969]

I was searching around tonight for a similar looking coral fossil imprint on quartzite and finally found it. A piece that I found at a shop in Austin years ago (unfortunately no ID with it). I need to take macro photos of it, so beautiful, but not the same as these sandy discs. 

[caldigger]

Kevin, I have some of these. I'll post ID when I get home.

 

Update: 

Hadrophyllum orbignyi ( Button Coral )

Devonian Period

Speed Limestone Formation

Clark County, Indiana 

[nivek1969]

10 hours ago, caldigger said:

Kevin, I have some of these. I'll post ID when I get home.

 

Update: 

Hadrophyllum orbignyi ( Button Coral )

Devonian Period

Speed Limestone Formation

Clark County, Indiana 

spot on! Thanks!