Species extinction across the cretaceous‐tertiary boundary: Observed patterns versus predicted sampling effects, stepwise or otherwise?

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Abstract
Stepwise extinction and origination patterns have been reported around the Cenomanian‐Turonian, Cretaceous‐Tertiary, and the Eocene‐Oligocene boundaries. Some of these observed stepwise patterns may result from only sampling effects. It is possible to test whether or not the observed stepwise patterns result from sampling effects if the appropriate information is known. An example of such a test involves the molluscan species from the Maastrichtian Prairie Bluff Chalk at Bragg, Alabama. Species abundances are known and sample sizes are 2144, 558, and 680 specimens from the lower, middle, and upper portions of the Prairie Bluff at Braggs. The observed ranges are not significantly different from the predicted values. These molluscs are representative of the Campanian‐Maastrichtian temperate fauna distributed from northern Mexico, through the U.S. coastal plain, to eastern Europe. This test suggests that this species‐rich and widely distributed fauna persisted unchanged until the latest Cretaceous.