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Species of the infraorder Cetacea A phylogenetic tree showing the relationships among cetacean families. [1]The evolution of cetaceans is thought to have begun in the Indian subcontinent from even-toed ungulates (Artiodactyla) 50 million years ago (mya) and to have proceeded over a period of at least 15 million years. [2]
Cetacea (/ s ɪ ˈ t eɪ ʃ ə /; from Latin cetus 'whale', from Ancient Greek κῆτος 'huge fish, sea monster') is an infraorder of aquatic mammals belonging to the order Artiodactyla that includes whales, dolphins and porpoises.
Ambulocetidae is a family of early cetaceans from Pakistan.The genus Ambulocetus, after which the family is named, is by far the most complete and well-known ambulocetid genus due to the excavation of an 80% complete specimen of Ambulocetus natans. [2]
The following is a list of currently existing (or, in the jargon of taxonomy) 'extant' species of the infraorder cetacea (for extinct cetacean species, see the list of extinct cetaceans). The list is organized taxonomically into parvorders, superfamilies when applicable, families, subfamilies when applicable, genus, and then species.
Cetacea (/ s ɪ ˈ t eɪ ʃ ə /; from Latin cetus 'whale', from Ancient Greek κῆτος 'huge fish, sea monster') [3] is an infraorder of aquatic mammals belonging to the order Artiodactyla that includes whales, dolphins and porpoises.
Whales do not form a clade or order; the infraorder Cetacea includes dolphins and porpoises, which are not considered whales in the informal sense. [citation needed] The phylogenetic tree shows the relationships of whales and other mammals, with whale groups [citation needed] marked in green.
The traditional theory of cetacean evolution was that cetaceans were related to the mesonychian. These animals had unusual triangular teeth very similar to those of primitive cetaceans. This is why scientists long believed that cetaceans evolved from a form of mesonychian.
The evolution of these sinuses also seems to have caused some restructuring of the skull base due to the development of bony walls surrounding the sinuses. The ectotympanic of all cetaceans, including Pakicetus and Ambulocetus , has a bony growth (involucrum) on the medial lip speculated to aid in the detection of low-frequency sounds.