a, Plot of the number of mysticete genera for each stage against time. b, Plot of the bizygomatic width (in centimetres) of the skull of mysticete specimens for each stage against time. The numbers on the graph indicate total body length estimates (in metres) for maximum and minimum bizygomatic width for each stage (see Supplementary Information for data and equation). The thick vertical line corresponds to the age of the sediments in which Leviathan was discovered. Pliocene is considered as a single time interval. Myr, millions of years.