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This chapter investigates how different taxa contribute to the 26-m.y. periodicity of extinction observed for marine animals from the middle Permian to Recent. Time series showing percent extinction at the genus level are presented for ten major taxonomic groups: foraminifera, corals, bryozoans, brachiopods, gastropods, bivalves, ammonoids, arthropods, echinoderms, and vertebrates. These groups, especially those with abundant fossil records, exhibit peaks of extinction at most points in the periodic sequence, indicating that periodicity is a property of the marine fauna as a whole and not produced by independent or idiosyncratic variations among a few taxa. Factor analyses of the time series support this conclusion: they show no clear selectivity among large taxonomic groups and indicate that the periodic extinction events, regardless of magnitude, were affecting a broad spectrum of taxa. This is consistent with the hypothesis that periodicity i s caused by clock-like environmental perturbations and not internal dynamics (recovery intervals or chaotic behavior) of faunal evolution. Averaged time series for the taxonomic groups display a peak of extinction in the Callovian Stage of the Middle Jurassic, where a periodic pulse has not been previously identified.

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