Geology 217 Invertebrate Paleontology

Ben Greenstein, Dept. of Geology, Cornell College

 

Isorophus cincinnatiensis, an edrioasteroid, encrusting a brachiopod from an Ordovician sea floor. Edrioasteroids are one of the oldest groups of echinoderms with representatives dating back at least to the Early Cambrian (535 million years ago), if not earlier into late Proterozoic time. The disc-shaped form of Isorophus is typical for many (but not all) edrioasteroids. These echinoderms encrusted hard surfaces, such as the brachiopod shell (Rafinesquina alternata) to the left. Normally rare in the fossil record, they may be found by the thousands on individual bed surfaces (which were presumably favorable to encrustation).  This photo and caption have been modified from the Paleontological Research Institution, an invaluable resource for North American paleontology.