"Fillmore Formation" The Fillmore Formation (Early Ordovician) is a mixed carbonatic-siliciclastic unit that accumulated on a rapidly subsiding platform. Orthoceratids, crinoids, sponges, early agnate fish and trilobites (Pseudocybele) are the main organisms that lived in this platform marine environment. Media: Adobe Photoshop. Click on arrows to get closer or view next illustration.