Dolphins and porpoises are toothed whales of the order Cetacea, suborder Odontoceti. Like their distant relatives, baleen whales, toothed whales are mammals that spend their entire lives in earth's waters. Most toothed whales are found in oceans, but some inhabit harbors and rivers. Odontoceti make up sixty-seven of seventy-seven cetacean species, in six families: river dolphins (five species), porpoises (six species), dolphins (thirty-two species), sperm whales (three species), white whales (two species), and beaked whales (eighteen species). All male toothed whales are larger than females. Male sperm whales, the largest toothed whales, are the largest toothed animals in the world. They grow to seventy-foot lengths and seventy-five-ton weights. Sperm whales dwarf all other Odontoceti-Herman Melville's "Moby Dick" was a male sperm whale. Like all whales, toothed whales are thought to be descended from a land animal, believed to have been an ungulate (hoofed mammal). However, their earliest ancestor was not the same as that of baleen whales.Why ancestors of toothed whales entered the oceans, seventy million years ago, is unknown. It may be that their return to the oceans was due to the need for anewfood supply or to escape frompredators.
Thanks for description - Animal life club