The
Tournaisian, the oldest age of the
Mississippian (also known as Lower Carboniferous), contains eight conodont biozones, 3 of which are defined by
Gnathodus species: • the zone of
Gnathodus pseudosemiglaber and
Scaliognathus anchoralis • the zone of
Gnathodus semiglaber and
Polygnathus communis • the zone of
Gnathodus typicus and
Siphonodella isosticha The
Visean, the second age of the Mississippian, contains four conodont biozones, two of which are defined by
Gnathodus species: • the
Gnathodus bilineatus Zone • the
Gnathodus texanus Zone The
Serpukhovian, the third or youngest age of the Mississippian, includes four conodont biozones, two of which are defined by
Gnathodus species: • the
Gnathodus postbilineatus Zone • the
Gnathodus bollandensis Zone == References ==