List of cetaceans

Cetaceans are descended from land-dwelling hoofed mammals, and the now extinct archaeocetes represent the several transitional phases from terrestrial to completely aquatic.

[1] Historically, cetaceans were thought to have descended from the wolf-like mesonychians, but cladistic analyses confirm their placement with even-toed ungulates in the order Cetartiodactyla.

When not cited or footnoted differently, these are from the IUCN Red List of Threatened Species (v. 2014.3; data current at 20 January 2015).

All right whales have no ventral grooves; a distinctive head shape with a strongly arched, narrow rostrum, bowed lower jaw; lower lips that enfold the sides and front of the rostrum; and long, narrow, elastic baleen plates (up to nine times longer than wide) with fine baleen fringes.

Toothed whales are active hunters, feeding on fish, squid, and in some cases other marine mammals.

The Delphinidae are characterized by having distinct beaks (unlike the Phocoenidae), two or more fused cervical vertebrae and 20 or more pairs of teeth in their upper jaws.

The Monodontidae lack dorsal fins, which have been replaced by tough, fibrous ridges just behind the midpoints of their bodies and are probably an adaptation to swimming under ice, as both do in their Arctic habitat.

The most obvious visible differences between the two groups are that porpoises have a less pronounced beak, and have spade-shaped teeth as opposed to conical.

The sperm whale characteristically has a large, squarish head one-third the length of its body; the blowhole is slightly to the left hand side; the skin is usually wrinkled; and it has no teeth on the upper jaw.

[31] (orange) Owen, 1853 (blue) The La Plata dolphin is the only species of the family Pontoporiidae and genus Pontoporia.

They are characterized by having a lower jaw that extends at least to the tip of the upper jaw, a shallow or non-existent notch between the tail flukes, a dorsal fin set far backwards, three of four fused neck vertebrae, extensive skull asymmetry and two conspicuous throat grooves forming a 'V' pattern (which aid in sucking).