Figure 3. Brain mass relative to maturity (assessed by body length) in six different species. The horizontal line in each species plot represents the length at maturity. Female killer whales (a) (O. orca) reach sexual maturity at about 460 cm body length and as young as 8 yr of age (Dahlheim and Heyning 1999), while male killer whales (b) reach sexual maturity at about 520 cm length when they are around 15 yr of age (Dahlheim and Heyning 1999). Female Common bottlenose dolphins (c) (T. truncatus) reach sexual maturity at a length of 235 cm and at an average age of 8–9 yr (Wells and Scott 1999), and males (d) reach sexual maturity at a length of about 245 cm and an approximate age of 10 yr (Wells and Scott 1999). Female striped dolphins (e) (S. coeruleoalba) reach sexual maturity at 180 cm and about 7 yr of age (Perrin et al. 1994); males (f) reach sexual maturity at about 185 cm and about 11 yr of age (Perrin et al. 1994). Female pygmy sperm whales (g) (K. breviceps) reach sexual maturity at about 266 cm body length (Caldwell and Caldwell 1989), and males (h) reach sexual maturity at about 270 cm length (Caldwell and Caldwell 1989). Female spinner dolphins (i) (S. longirostris) reach sexual maturity at a length of 165 cm and at an average age of 4–7 yr (Perrin and Gilpatrick 1994) while males of this species (j) attain sexual maturity at a length of about 160 cm and an approximate age of 7–10 yr (Perrin and Gilpatrick 1994). Lastly, female Dall's porpoises (k) (P. dalli) reach sexual maturity at 174 cm and about 5 yr of age (Houck and Jefferson 1999), and males (l) reach sexual maturity at about 175 cm and about 5 yr of age (Houck and Jefferson 1999).