Figure 7. Correlations of first differences of references with global cetacean richness (as sampled, not ranged through). 7.1. Correlation of GeoRef papers with cetacean genera. 7.2. Correlation of PBDB references with cetacean genera. Note that both display a positive correlation, but the relationship is much tighter with PBDB references, as one might expect. Note also that the GeoRef and PBDB reference samples are not independent since most of the PBDB references are in GeoRef and vice versa.