All whales belong to an order of marine mammals called Cetacea. Orcinus orca, commonly called orca, is a member of the suborder of toothed whales 'odontocetes', which includes sperm whales, beluga whales and over 40 species of dolphins and porpoises. The Orca is the largest member of the dolphin family, yet has probably been called a whale because of its size.
Like humans, orcas belong to the class Mammalia; they are warm blooded, have hair, breathe air and give birth to live young, which they nurse with milk secreted from mammary glands. At various stages of development the Orca fetus still possesses hair, four limbs and a tail, and remains of legs can be found buried deep in their hind muscles. X-rays of flippers also reveal arm, hand and finger bones that are similar to our own.
All mammals probably arose from a common ancestor about 120 million years ago. About 53 million years ago the ancestors of the deer, cattle and pigs invaded the seas, and evolved into the whales we see today. Toothed whales probably evolved around 30 to 40 million years ago, and the dolphin family, including orcas, evolved approximately 11 million years ago. In comparison Homo sapiens evolved just 100,000 years ago.
