Monday, March 4, 2013

Isorophus cincinnatiensis edrioasteroids from Ohio & Indiana

Edrioasteroids are related to Crinoids, Starfish and Echinoids and look a little like a cross between the latter two. They live attached to a hard substrate (usually a shell or hardground) and filter the water for their food. Below is a specimen I bought years ago on E-bay with two specimens attached to a Rafinesquina ponderosa brachiopod shell. I don't know the species of them but they are most likely Isorophus cincinnatiensis as that is the most common species found in the Ordovician aged rocks around Cincinnati, Ohio (from whence this fossil originated).

These next two specimens I collected myself from the Whitewater formation near Brookville, Indiana. both are attached to Rafinesquina ponderosa brachiopods. Specimen #1

Specimen #2

The Whitewater formation and other rocks around Cincinnati, Ohio are upper Ordovician aged which places them in the Hirnantian (ICS) or Richmondian (N. America) stages.


  1. Hello!! I just came across this post. Just wondering, what's the biggest R. ponderosa you have ever come across? I have a specimen of what I believe is a R. ponderosa that came from the States and it is nearly 7 cm across!! Is that size for the species too big?

    1. That seems a little big. Where did you find it? If you purchased it I would go back to the seller and ask them.