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.