Fig 4. Comparison of a larger short diver and a larger long diver.

An illustration of the differences in brain mass, cortical surface area, cerebellum mass, average neuron density, and maximum dive time between one female adult delphinid (Oo; A) and one female adult ziphiid (Zc; B) of similar body size. Zc, which can dive deeper than a mile and longer than an hour, has a smaller brain with fewer neurons than that of Oo, an animal of similar body size that performs shallower, shorter dives.