Cetaceans (order Cetacea) are an order of mammals containing all whales, dolphins, and porpoises. They are a monophyly of Even Toed Ungulates (artiodactyla). They are the mammals most adapted to aquatic living, Their forelimbs having evolved into flippers, but Cetacean backlimbs are tiny and vestigial. Many are known for their intelligence.
Cetaceans breath air, inhaling oxygen and exhaling carbon dioxide. They have blowholes (nostrils) on the top of their head to simply breathing. Often, a cloud of ‘steam’ appears while they exhale, which can allow species to be identified from a distance.
Most have poor eyesight, which is made up for by excellent hearing. Very greasy tears are shed from the eyes, protecting them from salt in the seawater. The lenses are mostly spherical. The ears are simply small holes near the eyes.
Toothed Whales (Suborder Odontoceti) are capable of echolocation. Using this, they can determine size, shape, movement, and texture of an object, as well as determining whether or not this is prey. Baleen whales (Suborder Mysticeti) do not have echolocation, as it would be useless since it’s prey, krill, is too small to be seen with this.
Toothed whales feed mainly on fish and squid whereas baleen whales eat krill. Toothed whales generally swallow prey whole whereas baleen whales use baleen made of keratin (the same substance as the human fingernail) that filter small prey from the water. A few baleen whales do not eat krill and plankton, but rather small fish. The Grey Whale also eats crustaceans off the sea floor.
All whales suckle their young and have hair (although quite small). They also exhibit warm bloodedness, another mammalian trait. They can be distinguished from fish by the fact that their tail moves up and down rather than side to side. This up down motion can also be seen in quadruped animals while running.