River dolphins: evolution

The term “river dolphins” or platanistoids has been traditionally used to include four recent odontocetes (Platanista, Lipotes, Inia, and Pontoporia) that live in freshwater and coastal environments and are not members of the other clades of odontocetes: Delphinoids, ziphiids, and physeteroids. Although it was previously assumed that Platanistoidea were monophyletic, since 30 years morphological and molecular studies have established a consensus on the para- or polyphyly of this superfamily. The modern genus Platanista now appears to be the only survivor of an early diverging group of odontocetes, the Platanistoidea, which was diversified and widely distributed during the Oligocene and the Miocene. Whereas this clade is generally thought to include the modern and fossil Platanistidae, and the fossil families Allodelphinidae, Squalodelphinidae, and Waipatiidae, the phylogenetic relationships of other presumable platanistoids, namely, Prosqualodontidae and Squalodontidae, are more debated. The three other extant genera of “river dolphins” (Inia, Lipotes, and Pontoporia) are now unambiguously included in the Delphinida, branching before the Delphinoidea.