GLOBAL PATTERNS IN LATE PALEOZOIC FORAMINIFERAL DIVERSITY AND BIOGEOGRAPHY

Large databases of Late Paleozoic foraminiferal origination and extinction events have been compiled for the cratonic North American and Eurasian-Arctic paleobiogeographic realms. Both databases show that rates of foraminiferal evolution were greater during the Late Paleozoic ice age (late Serpukhovian–early Sakmarian; ~320 to 290 Ma) than during the immediately preceding and succeeding non-glacial intervals. This pattern is opposite to that for brachiopods and other marine invertebrates. Maximum foraminiferal diversity in the Eurasian-Arctic realm occurred at the Pennsylvanian–Permian transition, whereas in cratonic North America it was somewhat earlier, in Middle Pennsylvanian (Moscovian) time. The two realms exhibited relatively high foraminiferal similarity throughout Mississippian time, but similarity decreased in Pennsylvanian time, reached lowest levels during the latest Pennsylvanian (Gzhelian) and then remained relatively low throughout the Permian. The onset of declining similarity in early Bashkirian time followed soon after the initial closure of the subequatorial Rheic Ocean, dated independently at late Serpukhovian to earliest Bashkirian on the divergence of δ¹³C values in marine waters on opposite sides of Pangaea. The diversity and similarity patterns show that increasing diversification was accompanied by increasing provincialism, but it is unclear whether there are causative linkages. Much of the increase in diversity is attributable to the dramatic radiation of fusulinoidean foraminifers, a group characterized by rapid evolutionary rates, whose origin also closely coincided with the Mississippian-Pennsylvanian transition. Large scale geographic isolation meant that fusulinoidean diversification occurred more or less independently in the North American and Eurasian-Arctic realms.