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Global diversity (dashed line) and mean alpha diversity (solid line) of Permo-Triassic tetrapod families. Extinctions are labelled as 1, Olson's extinction; 2, end-Guadalupian extinction; and 3, end-Permian extinction. Geological stages (Gradstein & Ogg 2004) are as follows: Ar, Artinskian; K, Kungurian; R, Roadian; W, Wordian; Ca, Capitanian; Wu, Wuchiapingian; Ch, Changhsingian; I, Induan; O, Olenekian; An, Anisian; L, Ladinian; Cr, Carnian.
