Thursday, March 26, 2009

Ordovician Pelecypod - Ambonychia

I am continuing to read the book A Sea without Fish by David L. Meyer and Richard Arnold Davis about Ordovician fossils published in January 2009. Here are some pictures of a pelecypod (clam) from Trimble County, Kentucky. It is interesting because in their book they deal mostly with Ohio locations but they mention the site this fossil came from on pages 125-129. Their focus is on the gastropod beds in the Marble Hill Bed Rowland Member of the Drakes Formation (Katian - Richmondian) but I found this a layer below that.

What is nice about this fossil is the aragonite shell is pretty much intact. It appears this is somewhat of a rare occurrence. Usually, just a mold is left as they say in the book (pages 129-130) the shell must have had a high content of organic material. Using the Fossils of Ohio book and A Sea without Fish, this clam must be Ambonychia sp. Meyer and Davis refer to this pelecypod as an Epibyssate form which is one that "is attached to objects that are beneath the actual sediment-water interface of the sea floor."(page 284). I guess this would be opposed to ones that burrowed into the sediment.

This specimen is about 1 cm wide and 1.8 cm long. I found another that was 2.9 cm wide and 3.9 cm long but it was just a mold with on partial shell line impressions left at the back end of the clam .

You can see some other fossils found in Trimble County, Kentucky at the KYANA webpage on Ordovician fossils.

Note the pictures can be clicked on it make them show up larger.