Data from: Late Cenozoic onset of the latitudinal diversity gradient of North American mammals

The decline of species richness from equator to pole, or latitudinal
diversity gradient (LDG), is nearly universal among clades of living
organisms, yet whether it was such a pervasive pattern in the geologic
past remains uncertain. Here, we calculate the strength of the LDG for
terrestrial mammals in North America over the past 65 My, using 27,903
fossil occurrences of Cenozoic terrestrial mammals from western North
America downloaded from the Paleobiology Database. Accounting for temporal
and spatial variation in sampling, the LDG was substantially weaker than
it is today for most of the Cenozoic and the robust modern LDG of North
American mammals evolved only over the last 4 My. The strength of the LDG
correlates negatively with global temperature, suggesting a role of global
climate patterns in the establishment and maintenance of the LDG for North
American mammals.