General aspects of the evolutionary history of whales and dolphins |
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Authors: | R Ewan Fordyce Lawrence G Barnes Nobuyuki Miyazah |
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Institution: | Department of Geology, University of Otago, P.O. Box 56, Dunedin, New Zealand;Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, California 90007 USA;Otsuchi Marine Research Center, Ocean Research Institute, Akahama 2-106, Otsuchi, Kamihei-gun, Iwate Prefecture, 028-11, Japan |
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Abstract: | Abstract The Cetacea are the most diverse and highly aquatically adapted group of mammals. Their fossil record extends back at least to the Middle Eocene ( ca 50 Ma), and they will possibly be found earlier, judging by the relatively highly evolved nature of the earliest known whales. The most likely terrestrial ancestors of whales are the mesonychids, primitive hoofed mammals with omnivorous diets. Recently discovered archaeocetes with large, mesonychid-like heads and dentitions and functional hind limbs reconfirm earlier ideas about the mesonychid origin of cetaceans and the amphibious nature of the earliest transitional forms. Fossil cetaceans are relatively abundant and diverse thoughout the world, and are now known from every continent, including Antarctica. Odontocetes evolved echolocation to locate food. Mysticetes developed bulk feeding adaptations. Both undoubtedly evolved from archaeocetes, and the monophyly of Cetacea is the most parsimonious present hypothesis. Chromosomal and molecular evidence has taken an increasingly important role in determining cetacean relationships, but fossils and classical comparative morphological studies remain a necessary and pivotal source of information about cetacean phylogeny. |
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Keywords: | Cetacea evolution fossil marine mammal systematics |
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