Gnathodus

Gnathodus is an extinct conodont genus in the family Idiognathodontidae.

Use in stratigraphy
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