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Abstract:
The recent dolphin Inia (Cetacea) inhabits the river systems of the Amazon and Orinoco. It is
proposed that these river dolphins originated in the Pacific coastal region. During the Upper Miocene Pacific prototypes migrated into the river mouths and inhabited the fresh-water basins newly formed
by the uplifting of the Andean Cordilleras during the Pliocene. During the Pleistocene the dolphins settled the river systems of the Amazon and Orinoco. Water quality (turbity, range of sight, acidity)
is one of the significant influences on speciation within the genus Inia.