Figure 4 in Delphinid brain development from neonate to adulthood with comparisons to other cetaceans and artiodactyls

Figure 4. Encephalization quotient (EQ) and body lengths. Body lengths are used as a general indicator for maturity of these animals. Three delphinids (Orcinus orca, Tursiops truncatus, and Stenella coeruleoalba) are compared with EQ and body length against two members of Physeteroidea (Kogia breviceps and Physeter macrocephalus) and one member of Phocoenidae (Phocoenoides dalli). In each case, EQ declines as the animal grows toward a mature body length and perhaps beyond. EQ was measured directly from brain masses, except for a few of the larger O. orca for which brain mass was calculated from endocranial volume. Body mass varies considerably in mature animals. As a result, EQ in mature T. truncatus varies from around 3 to 5 and in O. orca from about 1.5 to 3. One outlier EQ value of 2 from a male T. truncatus was from an overweight animal.