Dolphin Swimming. Dolphins Are A Widely Distributed And Diverse Group Of Aquatic Mammals. They Are An Informal Grouping Within The Order Cetacea, Excluding Whales And Porpoises, So To Zoologists The Grouping Is Paraphyletic. The Dolphins Comprise The Extant Families Delphinidae The Oceanic Dolphins, Platanistidae The Indian River Dolphins, Iniidae The New World River Dolphins, And Pontoporiidae The Brackish Dolphins, And The Extinct Lipotidae Baiji Or Chinese River Dolphin. There Are 40 Extant Species Of Dolphins. Dolphins, Alongside Other Cetaceans, Belong To The Clade Cetartiodactyla With Even-Toed Ungulates. Their Closest Living Relatives Are The Hippopotamuses, Having Diverged About 40 Million Years Ago

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alongside aquatic baiji belong brackish cetacea cetaceans cetartiodactyla chinese clade closest comprise delphinidae distributed diverged diverse dolphin dolphins eventoed excluding extant extinct families group grouping hippopotamuses indian informal iniidae lipotidae living mammals million oceanic order paraphyletic platanistidae pontoporiidae porpoises relatives river species swimming ungulates whales widely within world years zoologists