Physeteroidea is a superfamily that 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 the 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 long, and weighing about . The two kogiid species are much smaller, around in length, and weighing . 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. The eyes of physeteroids are unable to swivel in their sockets, and possess only a vestigial anterior chamber. Echolocation likely is a far more important sense to these animals than vision. Another common characteristic is the spermaceti, a semiliquid waxy white substance filling the 'case' or spermaceti organ in the whale's head, which plays a primary role in the production and directional manipulation of focused clicking sounds used for echolocation in the extant great sperm whale (Physeter macrocephalus). All three species dive to great depths to find food, although the sperm whale is believed to dive much deeper than either of the kogiids. Members of both families eat squid, fish, and even sharks. Gestation lasts from 9 to 15 months, depending on species. The single calf remains with the mother for at least two years, before being weaned. Physeteroids do not reach full sexual maturity for several years. All species congregate in 'pods' or herds, consisting of mostly females, calves, and adolescent males, although these pod sizes are typically smaller in