Foraminifers experienced increased taxonomic diversity, increased rates of origination and extinction and shorter mean species durations during the Late Paleozoic ice age (LPIA) than during the immediately pre- and post-glacial intervals, a pattern 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 was prone to high rates of extinction and speciation under the variable, cyclothemic conditions of the LPIA. Increased rates of evolution among non-fusulinoidean foraminifers during the LPIA also could be related in some way to glacioeustatically induced instability of neritic environments.

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