Upper Miocene to Pliocene shallow-water benthic foraminiferal assemblages from Venezuela, Panama, and Ecuador are compared to assess the effects of the constricting Central American Seaway on Caribbean and tropical Eastern Pacific biotas. Before the completion of the Panama land bridge, shallow-water marine environments and their faunas on either side of the Isthmus were more similar than they are today. The prediction is that the gradual separation of Caribbean and tropical Eastern Pacific waters resulted in the progressive differentiation of the two faunas. While uplift from the collision of the Panama arc with South America began to affect deep-sea circulation by the late Middle Miocene, and complete deepwater cutoff is generally dated to ~8 Ma, the timing of surface-water changes and the resulting divergence of Pacific and Caribbean neritic faunas remains unclear. The present study uses Upper Miocene and middle Pliocene benthic foraminifera from inner to outer neritic (<200m) deposits of northwestern Venezuela, Caribbean and Pacific Panama, and coastal Ecuador. The relationships between the assemblages are measured using similarity indices such as Simpson's and Jaccard's. As an additional characteristic of assemblages, the diversity of each sample is measured using Fisher's alpha. Assemblages deposited shortly before and after the ~8 Ma deepwater cutoff are compared, as well as those deposited during seaway closure, at ~3.5 Ma.