PALEOECOLOGY OF BONAPARTHERIOIDEA (MARSUPIALIA, POLYDOLOPIMORPHIA, BONAPARTHERIIFORMES). The wear pattern, occlusal movement, body mass, and diversity of Bonapartherioidea families are analyzed. Hypothesis for the dietary habits and possible extinction causes are developed. Bonaparteroids are divided into three groups according to the development of Phase II in the chewing cycle. Grinding facet 5 is not developed in Prepidolopidae, is slightly developed in Rosendolopidae, and is broadly developed in Bonapartheriidae and Gashterniidae. Lateral movements characterize the occlusion of Prepidolopidae and Rosendolopidae, while oblique movements are typical of Bonapartheriidae and Gashterniidae. During the Peligran age—Vacan subage, species of Bonaparteroids occupied frugivorous, insectivorous, and folivorous niches. From the Barrancan age to La Cantera fauna, they mostly occupied the granivorous and insectivorous niches. Bonaparteroids became extinct during the Eocene/ Oligocene boundary, probably associated with an abrupt fall in temperature and precipitations.