GLOBAL COOLING AND GLACIAL EUSTASY AS CONTROLS ON FORAMINIFERAL ORIGINATION AND EXTINCTION DURING THE LATE PALEOZOIC ICE AGE

Fossil occurrence records from 47 measured sections in the present-day High Arctic and Eurasia have been compiled by means of graphic correlation into a composite standard database for assessing rates of foraminiferal origination and extinction during the Late Paleozoic ice age (LPIA). Foraminifers experienced increased taxonomic diversity, increased rates of origination and extinction, and shorter mean lineage durations during the LPIA than during the immediately pre- and post-glacial intervals. This pattern is opposite to that exhibited by brachiopods and other marine invertebrates. Much, but not all of the increase in evolutionary rates can be attributed to the origin and rapid diversification of the fusulinoideans, a narrowly specialized group that may have been prone to high rates of extinction and speciation under the variable, cyclothemic conditions of the LPIA. Cooling of sea surface temperatures during the LPIA would have reduced the geographic range sizes and fragmented the habitats in which stenothermal, warm-adapted fusulinoideans could live. Habitat fragmentation and reduced range sizes, in turn, would be expected to accelerate rates of origination and extinction. Increased rates of evolution among non-fusulinoidean foraminifers during the LPIA also may be related in some way to glacioeustatically induced instability of neritic environments.