Figure 4.19. Latitudinal range versus standard deviation (in m.y.) for four plankton groups (from Spencer-Cervato et al. 1994). Note the higher standard deviations (interpreted as higher diachrony) for events with broader latitudinal ranges (i.e., cosmopolitan events). Also, note the relatively low standard deviation values for calcareous nannofossils, which are largely cosmopolitan. This suggest that they are particularly well suited for biostratigraphic correlations.