The sperm whale family or simply the sperm whales is the collective name given to three species of whale, the Sperm Whale, the Pygmy Sperm Whale and the Dwarf Sperm Whale. There are three different taxonomic interpretations of this 'family'. The last of these listed here is the one that has generally been used since 1998.
(see [1]) All three species are members of the Kogiidae family.
(see [2]) Physeteridae recognised as the single family with Kogiinae as a subfamily. Alternatively Physeteroidea is called a superfamily and contains Kogiidae as a family.
(see [3]) Two distinct families - Physeteridae and Kogiidae.
In any case there is complete agreement that there are two genera - Physeter containing one species - the Sperm Whale - and Kogia containing the Dwarf Sperm Whale and Pygmy Sperm Whale.
The common characteristic of each species is spermaceti, a semi-liquid waxy white liquid filling the case or spermaceti organ in the whale's head. See the individual species articles for further details.
References
Order Cetacea by Mead and Brownell in Mammal Species of the World, Wilson and Reeder (eds), Smithsonian Institute Press.
Cetacean Societies Field Studies of Dolphins and Whales, Mann, Connor, Tyack and Whitehead (eds), ISBN 0226503410
Rice, Dale W. (1998). Marine mammals of the world: systematics and distribution. Society of Marine Mammalogy Special Publication Number 4. 231 pp.
Spermwhales exhibit the greatest sexual dimorphism of any cetacean, with females averaging 10 m (35 ft) in length and a weight around 12 tonnes-1/3 to1/5 of the weight of their male counterparts (although size differences vary between oceans depending upon exploitation, when larger males in particular were targeted by whalers).
Spermwhales are masters of this discipline and may dive to depths of 2000 meters, where the hydrostatic pressure exceeds 200 atmospheres.
Spermwhales were easy prey for whalers as it was well known that members of a group would come to the aid of a companion in distress, so by injuring a single member of the pod, the whalers were often able to pick off the entire herd one by one.
Spermwhales probably split off from the ancestors of all present-day cetaceans about 20 million years ago, and they may be as closely related to the baleen whales as they are to other toothed whales and dolphins.
The bodies of spermwhales are laterally compressed, with a single blowhole on the left front of the head and a thick dorsal hump originating at the hindmost third of the body.
Spermwhales were hunted intensively by American whalers during the 1800s for the light oil of their heads, and by factory ships of several countries in the 1900s for their meat.
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