Latitudinal diversity gradients form one of the most dramatic and pervasive biodiversity patterns shared by both marine and terrestrial systems. However, the evolutionary dynamics underlying such gradients are highly controversial, in part because of the lack of empirical data. We propose to undertake comparative analyses of the species-level evolutionary dynamics that underlie marine latitudinal diversity trends using Eastern Pacific, Japanese, and Sakhalin Neogene molluscan faunas (0 - ca. 15 million years ago). We will quantify species origination and extinction rates for latitudinally arrayed biotic provinces along each coast using Lyellian Percentages, "backwards survivorship curves", and stratigraphic durations of species. In addition, we will investigate how variations in body size and life-habit attributes, both within and among clades, influence evolutionary rates and species durations. We will use the Eastern and western Pacific faunas as parallel natural experiments for testing hypotheses on diversity controls and the organization of biotic patterns along latitude. This comparative approach will allow us to factor out the regional effects of geological history, geography and other relevant variables, and to test for the generality of our results.