Description
Ohio Isorophus Edrioasteroid
- Isorophus cincinnattiensis
- Upper Ordovician
- Maysville Formation
- Springdale, Ohio
- The specimen is shown with a Quarter (.95″ tall) for size reference
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Edrioasteroids are an extinct group of primitive echinoderms whose geologic range is Early Cambrian to Late Pennsylvanian. Several authors have argued whether edrioasteroids could freely move about on the sea floor or were firmly attached to a hard substrate throughout post-larval life. The living animal would have resembled a pentamerously symmetrical disc or cushion. They were obligate encrusters and attached themselves to inorganic or biologic hard substrates (frequently hardgrounds or brachiopods).
In uncrowded conditions, edrioasteroids are circular in outline, but they become polygonal and abutting under crowded conditions.
Disrupted edrioasteroids are often found with the oral surface completely disarticulated or missing, but with a completely articulated peripheral rim. Apparently, the peripheral rim was firmly attached to the substrate and more strongly constructed than the oral surface and therefore better able to withstand wave activity, death and decay, and subsequent disarticulation than the oral surface. This firm attachment to hard substrates also suggests lack of movement.
