Rates of origination and extinction for marine animal genera dropped to low levels in latest Mississippian time, immediately after massive glaciers formed in the Southern Hemisphere and a second-order mass extinction occurred. Evolutionary turnover and diversity remained low for ∼50 m.y., shifting markedly upward precisely when extensive glaciation ended in Early Permian time. All diverse taxa with good fossil records experienced low rates of origination and extinction during this major ice age. Such sluggish rates would be predicted for faunas of shallow seas on or adjacent to a heavily glaciated supercontinent such as Pangea, where cool and highly seasonal thermal regimes should dictate that species have broad ecological niches, widespread geographic distributions, and large and relatively stable populations.

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