LOS MAMÍFEROS DE LA FORMACIÓN FRAY BENTOS (EDAD MAMÍFERO DESEADENSE, OLIGOCENO SUPERIOR?) DE LAS PROVINCIAS DE CORRIENTES Y ENTRE RÍOS, ARGENTINA

The Fray Bentos Formation, with outcrops in the Uruguayan and the Argentinean provinces of Corrientes and Entre Rios, has yielded several fossil vertebrates, mainly mammals, that permit its reference to the Deseadan land-mammal age (upper Oligocene?). At the Argentine sites, dasypodidid edentates (Euphractinae) and caviomorph rodents (Chinchillidae and Cephalomyidae) not previously cited for these localities, were recorded together with notoungulates Leontinidae, Mesotheriidae (Trachyteriinae), Interatheriidae (Interatheriinae), Hegetotheriidae (Hegetotheriinae) and Archaeohyracidae. The most abundant remains belong (as in most South American Tertiary associations), to representatives of the Order Notoungulata, which allow its assignment to the Deseadan land-mammal age s. l. : Prohegetotherium (Hegetotheriidae, Hegetotheriinae) and Trachyterus (= "Ameghinotherium"; Mesotheriidae, Trachyterinae) are characteristic of this age. The presence of an Archaeohyracidae, the biocron of which extends to the Deseadan land-mammal age, also agrees with this temporal assignment of the bearing sediments. The remains referred to Leontinidae belong to a different taxon from that described for the Fray Bentos Formation in Uruguay. This family has been recorded from the Mustersan to the Colhuehuapian land-mammal ages, but is characteristic of the Deseadan land-mammal age. Chinchillidae and Cephalomyidae are recorded since the Deseadan land-mammal age. However, certain features of the specimens from Corrientes Province are more similar to Colhuehuapian forms than to the Deseadan one. Dasypodidae is represented by a new taxon of Euphractinae Euphractini and fragmentary remains of a morphotype similar to Machylotherium. This genus is recorded in the Casamayoran and Mustersan land-mammal ages of Patagonia (Eocene). Consequently, this taxon does not conform with the age proposed for this formation. KEY WORDS. Argentina. Corrientes. Fray Bentos Formation. Deseadan land-rnammal age. Mammals.