Whale is the
common name for a widely distributed and diverse group of fully aquatic
placental marine mammals. They are an informal grouping within the infraorder
Cetacea, usually excluding
dolphins and
porpoises. Whales, dolphins and porpoises belong to the order
Cetartiodactyla with
even-toed ungulates and their closest living relatives are the
hippopotamuses, having diverged about 40 million years ago. The two parvorders of whales,
baleen whales (Mysticeti) and
toothed whales (Odontoceti), are thought to have split apart around 34 million years ago. The whales comprise eight
extant families:
Balaenopteridae (the rorquals),
Balaenidae (right whales),
Cetotheriidae (the pygmy right whale),
Eschrichtiidae (the gray whale),
Monodontidae (belugas and narwhals),
Physeteridae (the sperm whale),
Kogiidae (the dwarf and pygmy sperm whale), and
Ziphiidae (the beaked whales).
