The Tournaisian, the oldest age of the Mississippian (also known as Lower Carboniferous) contains eight conodont biozones, four of which contain Patrognathus species:
the zone of Siphonodella quadruplicata and Patrognathus andersoni (upper zone of Patrognathus andersoni)
the lower zone of Patrognathus andersoni
the zone of Patrognathus variabilis
the zone of Patrognathus crassus
References
^British Avonian (Carboniferous) conodont faunas, and their value in local and intercontinental correlation. FHT Rhodes, RL Austin, EC Druce, 1969, British Museum (Natural History)