group of Guaycurú-Charruan languages spoken in Brazil, Argentina, and Paraguay. Of the Guaycuruan tribes, formerly inhabiting the Gran Chaco, the best known include the Abipón (Callaga), Caduveo (also called Mbayá and Guaycurú), Mocoví (Mocobí), Payaguá (Lengua), Pilagá, and Toba. Many Guaycuruan-speaking groups acquired the horse from the Spaniards and became famous in the 17th and 18th centuries for their highly stratified, warlike societies. The Caduveo (Mbayá), for example, developed definite classes of nobles, serfs, and slaves. Such Guaycuruan tribes campaigned eastward across the Paraná River and northward into the southern Mato Grosso. Constant warfare and epidemics eventually reduced their numbers, and in the second half of the 20th century these tribes were either extinct or were being assimilated, primarily in Argentina.