More than 100 genera of fusulinids are distributed in the late Paleozoic geosynclines and adjacent marine shelves of Eurasia and the western hemisphere. Geographic distribution of these genera is uneven and forms the basis for recognizing 14 fusulinid faunal associations or subassociations which can be grouped into four faunal realms: Eurasian-Arctic realm (middle and late Carboniferous and earliest Permian), Midcontinent-Andean realm (Pennsylvanian and most of Permian), Middle Cordilleran realm (early Permian), and a Tethyan realm (middle and late Permian). A gradual concentration of endemic genera in the Tethyan realm and a gradual restriction of other genera to the Tethyan realm occurred during the Permian. By the middle of late Permian time, nearly all fusulinids became extinct, except in the Eurasian Tethyan seas where advanced members of the Schubertellidae and Staffellidae formed a distinctive association in the youngest fusulinid faunas.

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