Tabulates

[Jan Lester]

Went to visit my daughter in WI and we did some rock hunting on Lake Michigan. Up in Door County, at North Point, we found lots of tabulate fossils, several varieties. We kept seeing a weird bisected circular fossil, and since we couldn’t see many brachiopods or clams in the fossils, we couldn’t figure them out. One of the rocks I collected seemed to connect the circle and the halysites on the other side. Is this the base (holdfast, connection) of this coral, maybe?? I am showing another rock in which the bisected circle isn’t quite as worn as most. 

[Fossildude19]

The last 3 images look like a Halysites sp. coral.

The rest look like cross sections through brachiopods.

[FossilDAWG]

From top to bottom:

1.  not sure, maybe brachiopod cross section

2. high-spired gastropod

3. gastropod

4, 5, 6 (I'm assuming these are all the same specimen): chain coral growing on a pentamerid brachiopod.  4 & 5 shows the brachiopod; the straight line structure is an internal structure that is characteristic of pentamerids.

 

The chain coral may be a Halysites species, as Tim suggested.  It may alternatively be a species of Catenipora.  You would need a good section through the coral to tell the difference.  Both genera are typical of the Silurian in that area, as are pentamerid brachiopods.

 

Don