Thursday, May 14, 2009

A Devonian Cephalopod

One of the more interesting things to do is to pick up rock plates with lots of fossils on them when on collecting expeditions. They can then be studied later after a cleaning where a world of surprises can be revealed.

This rock plate was found in Clark County, Indiana and is probably Silver Creek Member of the North Vernon Limestone. The fossils seen on it are from the Devonian period (Eifelian). It has purple colored brachiopods (Athyris fultonensis (Swallow, 1860), Mediospirifer, or Devonchonetes (Muir-Wood, 1962)). I used the KYANA Geological website Devonian brachiopod section to come up with those names. I also found a few Phacops rana trilobite molts, crinoid stems and spines.

The focus of my attention is the funnel shaped fossil that is about 5 cm long and 5 mm wide at one end and 2 mm wide at the other. After my May 4, 2009 post about Dry Dredgers members identifying the Ordovician rock's funnel shaped fossil as a cephalopod I took a new look at this one. Even using a magnifying lens I cannot see signs of a texture. I was looking for rings that might show it is a deformed crinoid stem. I saw some evidence of manganese oxide dendrites at one end.

In addition, it would be interesting to know what the spines on this rock belonged to. I assume they came from a crinoid calyx but maybe it was spiny snail.

Geodized Crinod Calyx & Horn Coral - Heltonville, Indiana

Here are some pictures taken of a display case in the mineral section of the GeoFair 2009 in Cincinnati, Ohio.

These pictures are of geodized crinoid calyx or horn coral from Heltonville, Indiana (approximately 86 driving miles to the northwest of Louisville, Kentucky). What I found interesting is that I found rocks like this in Lake Cumberland, Kentucky that must be geodized calyx pieces. I will need to find those and post them.