Biostratigraphic implications of the first North American occurrence of the Upper Mississippian ammonoid Platygoniatites

The late Mississippian ammonoid family Delepinoceratidae is comprised of the genera Platygoniatites and Delepinoceras, and is considered one of the more biostratigraphically significant families for lower Namurian correlation (Manger et al., 1985). Platygoniatites, the earliest member, is known from eastern and southern Europe (Ruzhencev and Bogoslovskaya, 1971; Wagner-Gentis, 1963, 1980) and North Africa (Lemosquet et al., 1985). Despite its wide distribution, Platygoniatites is generally a rare member (with the exception of the southern Ural Mountains) of latest Visean and earliest Namurian faunas. It has never been reported previously from North America, though thousands of ammonoids have been collected here from age equivalent beds. The discovery of a new species of the genus in the late Mississippian faunas of east-central Nevada provides new data for precise correlation of the ammonoid zonations of Gordon (1970) to the type Namurian and indicates a need for revision of the current correlations between the southern Urals and northwestern Europe.