Figure 2
From: Phylogenetic review of tonal sound production in whales in relation to sociality
Optimization of group size in Cetacea (using natural log). Dark purple and blue colored branches indicate small groups and demark most of the 'basal' whales. More brightly colored (green, yellow and red) indicate larger groups. The phylogeny suggests gradual increase in group size in the lineage leading to Delphinidae, with independent evolution of huge groups (red) in several lineages and some reversals to smaller groups (e.g. Cephalorynchus hectori).