The conodont genus Ancyrodella in the middle Genesee Formation (lower Upper Devonian, Frasnian), western New York

Abstract

Conodont faunas with species of Ancyrodella are described from the upper Penn Yan Shale (Crosby Sandstone) and Genundewa Limestone of the middle Genesee Formation between Keuka Lake and Lake Erie. Three established species and three new species in the early phylogeny of Ancyrodella are discussed: A. rotundiloba (Bryant) early form, A. rotundiloba late form, A. crosbiensis n. sp., A. recta n. sp., A. triangulata n. sp., A. rugosa Branson and Mehl, and A. alata? Glenister and Klapper. Standardization of the taxonomic concepts pertaining to these species (and others in the genus) is necessary to ensure their continued biostratigraphic usefulness. The sequence of faunas in New York correlates well with the lower Frasnian sequence and numbered conodont zones described by Klapper (1985, 1989) in the Montagne Noire, France. A fauna with the late form of Ancyrodella rotundiloba and A. crosbiensis n. sp. in the Crosby Sandstone of the upper Penn Yan Shale correlates with Zone 2 of Klapper (1989). The Crosby fauna succeeds a Zone 1 fauna with the early form of Ancyrodella rotundiloba in the lower Penn Yan Shale. The Crosby fauna is succeeded in turn by a fauna in the upper Genundewa Limestone with A. recta n. sp., A. triangulata n. sp., A. rugosa, and A. alata?, which is correlated with Zone 3 even though the zonal markers, A. alata sensu stricto and typical forms of A. rugosa, first occur in the lower part of the overlying West River Shale.