ABSTRACT New dental and skeletal remains of Prothoatherium colombianus, from the Miocene of Huila Department, Colombia, are described and discussed. The species, originally described as a didolodontid condylarth, is an advanced proterotheriid litoptern closely allied to Prothoatherium species from the Colhuehuapian of Patagonia. This further substantiates the primitive aspect of the La Venta Fauna, from whence the Colombian species came. Prothoatherium colombianus is of special interest because it is the smallest known advanced proterothere and because it is skeletally morphotypic to Thoatherium, a Santacrucian genus and the most completely monodactyl known mammal. In body size, skeletal adaptations, and presumed diet, P. colombianus is most similar to small, cursorially-adapted, forest-dwelling Recent ungulates and rodents. This accords with the hypothesis that the La Venta assemblage represents a forest or woodland savanna community.