There are vastly more plants and animals in the tropics than elsewhere. In the past 100 years, many hypotheses have been investigated, but no concise answer to what drives tropical diversity has emerged. One reason is that the usual way of examining diversity, species richness, is only one possible descriptor. Other measures, such as morphological diversity, may be equally revealing, and comparisons between measures may provide still better resolution. I performed the first explicit comparison of species richness and morphological diversity of terrestrial mammal communities across latitude. Mammal com- munities differed in diversity of both body sizes and body shapes. Tropical sites were less size diverse and more shape diverse than predicted by random models. Polar sites were more size diverse and less shape diverse than predicted. The analysis indicated that different evolutionary and ecological factors determine community structure at different points along this latitudinal gradient.