Wednesday, January 5, 2011

Pea Sized Waldron Shale Fossil

This post shows a series a pictures of a small pea sized (3-6 mm) fossil found in the Silurian Period Waldron Shale of southern Indiana.  Is this some sort of small calyx, blastoid, or something else?

The top has a small 5 petal flower like pattern that reminds me of crinoid calyx.  It sort of reminds me of a Pisocrinus crinoid but the base is circle enclosed in a triangle shape on these fossils.  The tops on some of the fossils have points the bend inward which seems more like a blastoid.

If anyone has some identification ideas on these fossils, let me know.  Thanks!

UPDATE (1/7/2011): After reading some great comments about these specimens, I e-mailed Dr. Colin Sumrall at the University of Tennessee in Knoxville for advice.  He identified it as a member of  the Coronoidea and it is called Stephanocrinus gemmiformis.  It is somewhat of a confusing crinoid and he pointed out it is "basically a blastoid with erect arms".

The Paleontological Research Institution (PRI) of Ithaca, New York has picture of an adult Stephanocrinus (PRI 42977) of the Rochester Shale on their web site.  They note it was thought to be a blastoid but "lacks the food grooves and central mouth that blastoids have".  While it is rare in the Waldron Shale of Indiana and maybe more common in Tennessee Silurian exposures, PRI lists it is common in the Rochester Shale of New York.  As of this writing Indiana9Fossils is selling at least one specimen here.

Kenny has found some of these fossils as well and sent me some images he took with a microscope.  One can see a line like pattern on parts of the fossil plus a magnified view of the triangle shape on the fossil bottom.