The extant genus inhabits the river basins of South America, but the family formerly had a wider presence across the Atlantic Ocean.

[4] The Iniidae have other morphology common to species adapted to freshwater riverine habitats;[5] which include highly reduced or absent dorsal fins, so they do not become entangled in vegetation from the flooded terrestrial plains; and large, wide, paddle-like pectoral fins that allow maneuverability in confined areas cramped by vegetation.

The dentition of Iniidae dolphins is heterodont,[citation needed] having conical, small teeth that differ slightly in the front of the mouth.

[8][9][3] Martin in 2004 found supporting evidence that genetic exchange occurs between multiple sites on the Amazon, even places hundreds of kilometres apart.

[11][12] The family also includes three extinct genera described from fossils found in South America, Florida, Libya, and Italy.