The Cetacea are one of the most distinctive and highly specialized orders of mammals . Although hunting and other human activities have endangered most cetacean species, the outlook for many is improving.
Whales are highly specialized for life in the water.
Whales have streamlike bodies with highly compressed neck vertebrae, dorsal fins, and a tail with two finlike flukes arranged horizontally. Modern whales have greatly elongated anterior skull bones, and the nostrils are located on the top of the head, forming the blowhole . The forelimbs are specialized to form flippers, and the hind limbs and pelvis are extremely small and do not normally extend out of the body wall of the animal. Many odontocetes can navigate by echolocation , producing sound waves using a complex system of nasal sacs and passages, and using the echoes to navigate. Dolphins and porpoises are examples of odontocetes, as are belugas, narwhals, killer whales, sperm whales, and beaked whales.