Thursday, February 6, 2020

Cast of Large Ambonychia Clam Fossil with Bryozoan

This fossil mold appears to be an Ambonychia clam with both valves and is big enough to almost cover the palm of a hand. The clam fossil may have several colonies of cyclostome bryozoan (though only their holdfasts remain). I don't see where the zooids would bud out of their protective structures.The branching pattern seen in the pictures can be found on quite a few clam molds at the site this fossil was collected.
On both sides there are remnants of another bryzoan in what seems to be Prasapora simulatrix.

It looks like the shell eroded away and the bryozoan set up shop on the mold but on both sides. Not sure how this was accomplished at the same time which leads me to believe they grew on one side till the fossil was turned over and then new colonies grew on this water exposed side. Just a theory...

This fossil was found in Bullitt County, Kentucky, USA. It might be from the Grant Lake Formation. The fossil dates to the Ordovician Period.