Mammalian order Cetacea
INTRODUCTION
The mammalian order Cetacea, including whales, dolphins and porpoises, has at least 79 species and is represented in all oceans and some large river systems of Asia and South America. There are three Suborders: the Archaeoceti, the Mysticeti, and the Odontoceti.
The Archaeoceti or "ancient whales" are extinct and known only by fossils. The Odontoceti or "toothed whales" have either numerous, uniform and conical teeth, asymmetrical skull and single nasal passage. The Mysticeti or "baleen or whalebone whales" are named after their feeding apparatus; a series of transverse plates of comb-like baleen (made of similar material to that of the human fingernail) which descend from the roof of the mouth and serve to strain plankton and small fish. Other distinctive characteristics of the baleen whales include a symmetrical skull with no melon (the apparatus used by odontocetes for echolocation) and a pair of nasal cavities.
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