are those cetaceans which are neither dolphins (i.e. members of the families Delphinidae or Platanistoidea); nor porpoises. This can lead to some confusion because Orcas ("Killer Whales"); and Pilot whales have "whale" in their name, but they are dolphins for the purpose of classification.
All cetaceans, including whales, dolphins and porpoises, are descendants of land-living mammals of the Artiodactyl order (even-toed ungulate animals);. Both cetaceaos and artiodactyl are now classified under the super-order Cetartiodactyla which includes both whales and hippos. In fact, whales are the closest living relatives of hippos; they evolved from a common ancestor at around 54 million years a;. Whales entered the water roughly 50 million years a;.
Cetaceans are divided into two suborders:
- The baleen whales are characterized by baleen, a sieve-like structure in the upper jaw made of keratin, which they use to filter plankton from the water. They are the largest species of whale.
- The toothed whales have teeth and prey on fish, squid, or both. An outstanding ability of this group is to sense their surrounding environment through echolocation.