[2] Carneiro and Oliveira (2017) considered the species Eobrasilia coutoi from the early Eocene (Itaboraian) of Brazil to be a stagodontid;[4] if confirmed it would make it the only known Cenozoic and the only known South American member of the family.

Stagodontids were some of the largest known Cretaceous mammals, ranging from 0.4 to 2.0 kilograms (0.88–4.41 lb) in mass.

[5] One of the most unusual features of stagodontids are their robust, bulbous premolars, which are thought to have been used to crush freshwater mollusks,[6] a diet that apparently evolved independently at least twice within this clade.

[8][9] The most well described forms are found in Laramidia, but they are also present on Appalachian and South American sites, further leading credence to their aquatic habits.

[12] Stagodontids were once thought to be closely related to the Sparassodonta, but later studies suggest they belong to a more ancient branch of the metatherian family tree, possibly closely related to pediomyids,[13][14] being in particular closest to Pariadens, which forms the immediate outgroup to Stagodontidae.