Two mass extinctions brought the Paleozoic to a close: one at the end of the Guadalupian, or middle Permian (ca. 260 Ma), and a more severe, second event at the close of the Changhsingian Stage (ca. 251.6 Ma). Here we review work over the past decade that defines the probable causes of the mass extinction, and evaluate several extinction hypotheses. The marine extinctions were selective; epifaunal suspension feeders were more affected than other clades, although significant variations occurred

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... ven among the filter feeders. In southern China, the Changhsingian marine extinction was nearly catastrophic, occurring in Ͻ0.5 m.y. On land, vertebrates, plants, and insects all underwent major extinctions. The event coincides with (1) a drop of d 13 C in carbonates, from ϳ‫‰2‬ to ‫‰2‬ in both marine and terrestrial sections; (2) the eruption of the massive Siberian continental flood basalts; and (3) evidence of shallow-water marine anoxia, and perhaps deep-water anoxia. Although the cause of the extinction remains unclear, a series of constraints on speculation have been established in the past few years. Leading contenders for the cause are the climatic effects, including acid rain and global warming, possibly induced by the eruption of the Siberian flood basalts; and marine anoxia. An extraterrestrial impact is consistent with the geochronological and paleontological data from southern China and elsewhere, and some possible evidence for impact has recently been advanced.