Ptilodictyoid Cryptostomata Bryozoa from the Middle and Upper Ordovician Rocks of Central Kentucky

Abstract

The High Bridge Group (Middle Ordovician), and the Lexington Limestone and Clays Ferry Formation (Middle and Upper Ordovician), of central Kentucky contain a diverse fossil invertebrate fauna, including cryptostome ptilodictyoids, the so-called “bifoliates,” as a distinctive element. The ptilodictyoid bryozoans there include nine species of six genera Escharopora, Graptodictya, Phyllodictya, Stictopora, Trigonodictya, and new genus Orectodictya in two families Ptilodictyidae and Rhinidictyidae. Three species are new: Escharopora eparmata, Trigonodictya cirrita, and Orectodictya pansa. Most of the species are closely related to ptilodictyoids occurring in the Middle Ordovician of New York and Minnesota. In Kentucky, Escharopora, Stictopora, and Trigonodictya occur in the oldest rocks exposed, and thus include the oldest bryozoans found in Kentucky. The stratigraphic distribution of ptilodictyoids in Kentucky reflects the disconformable contact between the Tyrone Limestone (High Bridge Group) and the overlying Lexington Limestone.