Caesar Creek Lake Fossil

[Edward Engelbrecht]

Greetings. I am new to the forum and this is my first post. I'm an amateur collector in Ohio who recently visited the Caesar Creek park and came back with a fossil I can't identify. Here is data about the site:

Liberty and Whitewater Formations (Camp, Roadside Geology of Ohio, p. 61)

Classified Ordovician

Limestone and Shale

 

The fossil is just over six centimeters long. It washed out of the formation naturally; I've done minimal preparation. The fossil has a flattened cone shape. One end has a distinct point, the surface is pitted and wrinkled (skin-like), and there are parallel lines on the opposite end. There are ribbed, tube structures on one side, which I believe are separate fossils (Cornulites or Tentaculites? Thompson, National Audubon Society Field Guide to North American Fossils, entries 345, 346). I polished one edge with parallel lines to see internal structure. When I saw the fossil on the ground, I thought, "Large bivalve" because of the parallel lines. But it is not a bivalve. Though it has a cone-like shape, it also does not look like the horn corals I picked up at the same location. Suggestions would be greatly appreciated.

[Tidgy's Dad]

It is the bivalve Ambonychia, I think. 

There are several species in those formations. 

[Tidgy's Dad]

It's a big specimen with a noticeably triangular beak, so I would lean towards A. robusta.   

[FossilDAWG]

Welcome to the Fossil Forum!!

 

I agree with the Ambonychia suggestion.  I'll also note that bivalves and gastropods in the Cincinnatian formations are generally preserved as internal and external molds, with no actual shell material, as appears to be the case with your fossil.  However you can sometimes find specimens with mineralized or replaced shell, especially the gastropod Cyclonema and occasionally pectinid bivalves including Ambonycia.  This is due to differences in the original shell composition, as calcitic shells are more resistant than aragonitic shells.

 

Don

[Mark Kmiecik]

My immediate thought when I saw it was bivavle.

[ClearLake]

As Adam and others mentioned, a nice Ambonychia from a site I visited many times early in my fossil hunting life.  It is a nice place to go.  Congrats and welcome to TFF!

[Ludwigia]

I agree with the others.

[Edward Engelbrecht]

Thanks, everyone. Very helpful.