During the early to middle Miocene of the Atlantic and Indian Oceans there were variations in species diversity of the lower bathyal to abyssal plain (3-4.4 km) benthic foraminiferal assemblages although, overall, diversity remained high and comparable with that of the modern environment. The early Miocene was a period of palaeoceanographic change and this has previously been documented both through studies of stable isotopes and the rate of appearances or disappearances of taxa (whether evolutionary or ecological). The diversity oscillations appear to represent shorter period change. The lowest diversities are associated with the peak abundance of bolivinids. Other variations cannot be correlated from one site to another and are thought to represent local environmental changes. During the early-middle Miocene, the diversity of the Atlantic abyssal plain was lower than that of the Indian and Pacific Oceans possibly indicating significant diversity differences between ocean basins. On the basis of limited data, it is possible to speculate that the species diversity of the Miocene was perhaps higher than that of today.