Cetacea , (from
Latin cetus "large sea creature" and
Greek ketos "sea-monster") are a widely
distributed and diverse
infraorder of
carnivorous, aquatic,
marine mammals. They comprise the
families Balaenidae (
right whales),
Balaenoptera (rorqual),
Eschrichtiidae (the
gray whale),
Delphinidae (oceanic dolphins),
Monodontidae (Arctic whales),
Phocoenidae (porpoises),
Physeteridae (the
sperm whale),
Kogiidae (lesser sperm whales),
Platanistidae (Old World
river dolphins),
Iniidae (New World river dolphins),
Pontoporiidae (the La plata dolphin), and
Ziphidae (beaked whales). There are currently 88 species of cetacean. While cetaceans were historically thought to have descended from
mesonychids,
molecular evidence supports them as descendants of
Artiodactyla (even-toed ungulates). Cetaceans belong to the order Cetartiodactyla (derived from Cetacea and Artiodactyla) and their closest living relatives are
hippopotamuses, having diverged about 60 million years ago.
