Microevolutionary processes operating over short time scales potentially influence evolutionary trajectories and patterns occurring on much longer time scales. While this possibility has been recognized for some time, empirical evidence for long-term evolutionary consequences of short-term events is limited. Evolutionary trends in three groups of fossil marine invertebrates (ammonoids, belemnoids, and planktonic foraminifera) from the Cretaceous and Cenozoic that lived for many millions of years were examined. Results suggest that short-lived evolutionary changes in the magnitude of variance and mode of natural selection can profoundly influence long-term patterns of evolution. Although the short-term events studied did not appear to alter mean adaptive values and selective equilibria, they caused dramatic differences in the pace of evolution and morphological consequences. These results provide insight into factors influencing evolutionary patterns on long time scales.