Evolutionary Morphology of the Dolphin Brain
P. J. Morgane
Worcester Foundation for Experimental Biology
M. S. Jacobs
New York University Dental Center
Harvard Medical School and Beth Israel Hospital
Studies of the cetacean brain are expected to shed considerable light on mammalian brain evolution and, in particular, on how the brain has adapted to markedly differing environments, such as between land and water. To date, although there have been numerous studies on different aspects of cetacean brain anatomy, what has been lacking is integration of this information with that available from studies of evolutionary neuroanatomy. Relative to this, the cetacean brain has historically often been given special status based on its size and fissural complexity rather than on the microscopic appearance of the cortical formations comprising its main divisions.
Before considering the status of the dolphin brain, it should be noted that development and formation of the neocortex of mammals and reptiles took place in a land environment, which shows much more diurnal and seasonal variation than does an aqueous environment. The cetaceans are a major Order of mammals showing a complete secondary return to an aqueous medium. Genetically related to all terrestrial mammals, the cetaceans are of particular evolutionary value and uniqueness, since they have adapted themselves to activity in an aqueous medium according to evolutionary laws characteristic of the whales alone. In doing so they exemplify the potential possibilities of environmental changes on the structural organization of the brain, in particular, the great adaptability of the cortical