At any location, a group of organisms may be represented by several clades. What determines which clades will dominate local communities in terms of their species richness? Here, this relatively neglected question is addressed by analyzing 166 local assemblages of snakes distributed globally. For most regions, local assemblages are dominated by clades with higher global-scale diversification rates and more frequent dispersal into each region, and not by clades that have been present in that region longer. This result contrasts with many other studies of local richness (in other organisms), which show strong impacts of regional colonization time on overall local species richness of clades. Furthermore, even though local assemblages are assembled independently on different continents, most regions have converged on similar patterns of proportional richness. Specifically, a few rapidly diversifying clades dominate most communities around the world. The high diversification rates of these clades are then linked to their high dispersal rates. Similar patterns may occur in many groups, such as plants, frogs, salamanders, birds, and mammals.