R.L. Reep T. J. O'Shea 1990 <p><span>Relative brain size in the Sirenia is unusually small. Encephalization quotients are 0.27 for Florida manatees (</span><i>Trichechus manatus</i><span>) and 0.38 for dugongs (</span><i>Dugong dugon</i><span>). Estimates for Steller's sea cow (</span><i>Hydrodamalis gigas</i><span>) range from 0.12 to 0.19. These values are among the lowest known for Recent mammals, and seemingly have changed little since the Eocene. A body plan specialized for the aquatic environment does not account for low encephalization quotients; values are substantially less than predicted based on cetacean or pinniped allometry. Life-history, ecological, and behavioral traits of the Sirenia are typical of relatively large-brained species. Low quality food and a low metabolic rate, however, are characteristic of the Sirenia and other small-brained mammals. Acting through prolonged postnatal growth, selection also likely favored large body size in the Sirenia without a correlated increase in brain size.</span></p> application/pdf 10.2307/1381792 en Oxford University Press Encephalization quotients and life-history traits in the Sirenia article