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Caviomorph rodents became important components of South American faunas after their Eocene arrival from Africa. Here we describe the cavioid, chinchilloid, and erethizontoid caviomorphs of the early Miocene Pampa Castillo fauna of southern Chile. This fauna's age and location make it key for resolving outstanding biostratigraphic questions concerning early Miocene Patagonian fossiliferous strata.Each of the four major caviomorph clades ("superfamilies") is represented in the Pampa Castillo fauna, three whose members are detailed here: cavioids (3 genera; 3 species), chinchilloids (3 genera; 6 species), and erethizontoids (2 genera; 2 species).Abundantly represented taxa, e.g., Neoreomys australis, Perimys erutus, and Prolagostomus pusillus, corroborate previous work assigning the Pampa Castillo fauna to the Santacrucian South American Land Mammal "Age" (SALMA; inclusive of the "Pinturan"). Several taxa, including Eosteiromys, Perimys intermedius, and Perimys sp. nov.?, are also found in the lower and middle Pinturas Formation (ImPF) but not "core" Santacrucian faunas (from the Santa Cruz Formation [SCF] along the Rio Santa Cruz and Atlantic coast), suggesting a distinctive

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The Salla Beds of Bolivia reveal a rich, late Oligocene (Deseadan, South American Land Mammal "Age") fauna composed of at least 50 mammalian species. Many taxa (e.g., rodents and typotherian notoungulates) are represented by dozens to hundreds of specimens. Litopterns are much less common but are represented by one macraucheniid and two adianthid species. Until now, only fragmentary postcrania of proterotheriids have been described from Salla. The recent discovery of a maxillary fragment with two molars, examination of previously recovered mandibular fragments, and a phylogenetic analysis, allow us to recognize Promylophis cifellii gen. et sp. nov. It is characterized by small size, absence of a metaconule on M1-2, and lower molars with a short "paracristid" and reduced or absent "paraconid." Postcranial elements referred to cf. P. cifellii resemble geologically younger (e.g., Miocene) proterotheriids by way of anatomically tridactyl, but functionally monodactyl pes, and distal femora with a supra-trochlear fossa that forms a "patellar pit" that appears to function as a passive stay apparatus for the knee joint. Such a mechanical means of diverting forces from muscle to bone and sinew could save biologically significant amounts of metabolic energy in long-standing animals. http://zoobank.org/urn:lsid:zoobank.org:pub:A9DF310C-FD5B-45A0-B605-8CD7101920B3