Physeteroidea

Physeteroidea is a superfamily that, today, includes three extant species of whales; the sperm whale, in the genus Physeter, and the pygmy sperm whale and dwarf sperm whale, in the genus Kogia. In the past, these genera have sometimes been united in a single family, the Physeteridae, with the two Kogia species in a subfamily (Kogiinae); however, recent practice is to allocate the genus Kogia to its own family, the Kogiidae, leaving the Physeteridae as a monotypic (single extant species) family, although additional fossil representatives of both families are known.

Characteristics

The sperm whale (Physeter macrocephalus) is the largest species of toothed whale, with adult bulls (males) growing to be about 15–18 m (49–59 ft) long, and weighing about 45–70 metric tons (44–69 long tons; 50–77 short tons). The two kogiid species are much smaller, around 2.5 to 3.5 m (8 ft 2 in to 11 ft 6 in) in length, and weighing 350–500 kg (770–1,100 lb).

The bodies of physeteroids are robustly proportioned, with paddle-shaped flippers. The lower jaw is always relatively small and thin relative to the upper jaw. The nasal bones of these whales are distinctly asymmetrical, with the blowhole being located on the left side of the head; in the sperm whale, this is near the top of the head, while on the kogiids it is further forward. All species have a large number of similar, and relatively simple, teeth. In the kogiids, and sometimes also in the sperm whale, the teeth in the upper jaw do not erupt, and are sometimes altogether absent.