Middle Devonian Chitinozoa of Indiana

Abstract

Middle Devonian chitinozoans from the Muscatatuck Group of Indiana belong to eight species of the genera Alpenachitina, Ancyrochitina, Angochitina, Eisenackitina, and Hoegisphaera. The Chitinozoa are most abundant in the carbonate rocks that represent well-circulated open-water conditions and are low in diversity or are absent from lithographic and laminated dolomite representing the shallower, more restricted environments. The local range zones of the chitinozoans from the Muscatatuck Group, when compared with the occurrence of similar taxa from correlative strata in the midwestern United States, are quite parallel to the established conodont zones. The lowest occurrence of Alpenachitina eisenacki, Angochitina callawayensis, and Eisenackitina inflate in the lowermost rocks of the Muscatatuck Group is in the Icriodus latericrescens robustus Zone, which is early Eifelian in age. Ancyrochitina hamiltonensis in association with A. cf. A. spinosa and Hoegisphaera glabra characterizes the upper part of the Muscatatuck rocks, and the occurrence of those chitinozoans ranges from the upper part of the late Eifelian I. angustus Zone into the early Givetian I. latericrescens latericrescens Zone.