The orca (Orcinus orca), also known as the killer whale, is a species of large toothed whale in the oceanic dolphin family Delphinidae. They are the only extant species in their genus, and are among the most intelligent animals in the world; they are believed to be culture-forming animals. Their ancestors evolved approximately 3.5 million years ago, during the Pliocene age. Orcas are the largest of the dolphins, growing up to 26 feet long in males. Some marine biologists believe that orcas may actually constitute a few different species which can be recognized based on their habitat, anatomy, and behavior, but the precise number of species or subspecies is still being researched. They are found in surface waters in all of the world’s oceans, avoiding only regions where ice caps are too thick to break without injury. Some populations of orcas are considered endangered, but overall, the International Union for Conservation of Nature cannot assign a single conservation status to the orca because its taxonomy is so unclear.
