Pragian conodont zonal classification in Nevada, western North America

Abstract

A tripartite global zonal scale for the Pragian Stage (Devonian) was recommended by the Subcomission on Devonian Stratigraphy in 1989. Since that time, additions to the data on the two primary lineages used for the subdivision of the Pragian, Eognathodus and early Polygnathus, have shown: 1) that the Lochkovian-Pragian boundary criterion is useable as defi ned and is applicable on a global scale, but that the boundary-stratotype section in the Barrandian region of the Czech Republic has serious limitations as a reference section; 2) the criteria for the internal subdivision of the Pragian are not globally applicable; and 3) that the taxon that we have used in Nevada to mark the base of the Emsian is Polygnathus lenzi, whose range may be different from that of Australian P. dehiscens, the supposed criterion for the base of the Emsian.

This paper reviews the Pragian of Nevada and compares it with Alaska, Canada, eastern Australia, and central Europe and suggests a regional scale for use in the western North American Cordillera.

The subdivisions proposed here (irregularis-profunda Zone; profunda–brevicauda Zone; brevicauda-mariannae Zone; mariannae-lenzi Zone) are not the same of the SDS and cannot be applied on a global scale. The first two are based on evolutionary appearances; the last two on the lowest occurrences of distinctive and widespread taxa in North America.

One new genus, Masaraella and four new species, Masaraella epsilon, Masaraella riosi, Gondwania profunda, and Pedavis longicauda, are described.