ABSTRACT
Cetaceans are among the most intelligent of mammals and their adaptation to a fully aquatic lifestyle represents one of the most dramatic transformations in mammalian evolutionary history. Significant modifications occurred at all levels of physiology, morphology and the nervous system. Among the most dramatic but less overt evolutionary changes are those that occurred in the brain. Many cetacean species possess the largest brains of all animals. The most massive brain on Earth belongs to the modern sperm whale(Physeter macrocephalus) with an average adult brain size of about 8000 grams (Marino, 2002) as compared with an average adult human brain of approximately 1300g. And, in addition to absolute size, modern cetacean brains are among the largest in relation to body size.
