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Dinomyidae is a South American group of caviomorph rodents with a single extant species (Dinomys branickii), but with a rich fossil record including medium-sized to giant species, which reached its peak diversity during the Late Miocene. The dinomyids from the Cerro Azul Formation (late Middle Miocene to Early Pliocene) have been studied in detail from localities in La Pampa Province, Argentina. In this contribution, dinomyids from Chasicoan Stage/Age (Late Miocene) levels of the Cerro Azul Formation at Arroyo Chasicó locality (Buenos Aires Province, Argentina) are revised, including previously published material and unpublished ones. We confirm the presence of Tetrastylus sp. Diaphoromys gamayensis, and define two new taxa, Bondesiomys chasiquensis gen. et sp. nov. and Gyriabrus sokka sp. nov. The diversity of dinomyids from the Cerro Azul Formation at Arroyo Chasicó is higher than other Chasicoan faunas at the same latitude, identified in localities of La Pampa Province, since in Cerro Patagua there are not Dinomyidae records and in Cerro la Bota Tetrastylus sp. and Dinomyidae indet. were the only recorded taxa. [ABSTRACT FROM AUTHOR]

Phoberomys is a giant caviomorph rodent included in the extinct Neoepiblemidae. It is recorded in the late Miocene-Pliocene of South America (Argentina, Venezuela, Brazil and Peru), and is one of the largest rodents that have ever lived. In this contribution we study specimens of Phoberomys from the ‘Mesopotamiense’, late Miocene of Entre Ríos Province (Argentina), including several unpublished specimens and the holotypes of the five nominal species (Ph. burmeisteri, Ph. praecursor, Ph. insolita, Ph. lozanoi and Ph. minima) previously recognised for this unit. Our study indicates that all Mesopotamian specimens belong to Phoberomys burmeisteri, and that the differences among them reveal individual and ontogenetic variation. Our phylogenetic analysis indicates that Neoepiblemidae is monophyletic and includes Phoberomys, Neoepiblema, and Perimys. Phoberomys species are recovered as a clade, which is more closely related to Neoepiblema than to the Patagonian Perimys. In addition, our study shows that Eusigmomys is not a Neoepiblemidae, but a Dinomyidae. [ABSTRACT FROM AUTHOR]