Toward an improved Silurian conodont biostratigraphy

Abstract

Silurian conodonts have been widely reported and many species have worldwide distribution. However, present zonations utilizing them have many limitations and no single scheme provides a suitable standard. A good standard zonation for Silurian conodonts is desirable, but impossible at our present state of knowledge. Environmental differentiation, the rapid evolution of several unrelated conodont lineages and the lack of distributional data are the principal factors producing this situation. Existing Silurian conodont zonations are evaluated, and zonal schemes based on well documented phylogenetic lineages are advocated. Eight datum planes are proposed as an additional biostratigraphic framework in the system. These are the Distomodus staurognathoides Datum, Pterospathodus amorphognathoides Datum, Pterospathodus Extinction Datum, Kockelella walliseri Datum, Kockelella variabilis Datum, Ancoradella ploeckensis Datum, Kockelella Extinction Datum and Ozarkodina crispa Datum. Six of these datum planes are based on the evolutionary appearance of the datum-defining species. Extinction datum planes correspond to a significant level of extinction amongst the conodont-bearing animals.