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The present paper deals with the leontiniid remains recovered from the Late Oligocene (Deseadan) levels of Quebrada Fiera, Mendoza Province, central-western Argentina. The material consists of an almost complete skull associated with 11 vertebrae, as well as some maxillary and mandibular fragments and postcranial elements of different individuals, enabling a life reconstruction. The comparative study allows morphological differences with respect to other Deseadan taxa to be established, such asScarrittia,Leontinia,Ancylocoelus,AnayatheriumandElmerriggsia, leading to the proposal of the new taxonGualta cuyanagen. et sp. nov. The new genus and species is close toScarrittia canquelensisin having upper I1 more developed than I2–3, mainly by its greater crown-height, and the canine overlapping the P1; it differs from this species by the longer, narrower nasals, longer rostrum, I2 not reduced, P3–4 with shallow lingual sulcus, shorter cervical vertebrae, and shorter calcaneum, lacking navicular facet. The complete dentition and/or the larger I1 differentiateGualta cuyanafromLeontinia,AncylocoelusandAnayatherium ekecoa, as well as from the MioceneColpodon. The lingual sulcus on P3–4 is much shallower than inScarrittia barranquensis,Leontinia,AnayatheriumandElmerriggsia. The phylogenetic analysis shows poorly resolved relationships among leontiniids; when using equal weights, the analysis shows thatGualta cuyanais more related to the species ofAnayatheriumandScarrittia canquelensis, whereas under implied weights, the new taxon is basal to other Palaeogene taxa.Gualta cuyanaadds to other endemic taxa of the peculiar Deseadan assemblage from Quebrada Fiera. The new leontiniid constitutes a low percentage of fossil mammals within the Quebrada Fiera fauna, as is also true for this family in Salla (Bolivia), but in contrast with some Patagonian localities or the Brazilian Tremembé Formation where leontiniids are the best-represented mammal group. http://zoobank.org/urn:lsid:zoobank.org:pub:17749C84-4028-4FC8-A140-E1A6FE02466D [ABSTRACT FROM PUBLISHER]

We describe a new metatherian mammal,Fieratherium sorexgen. et sp. nov., found in western Argentina (Quebrada Fiera locality, southern Mendoza Province), in Late Oligocene deposits (Agua de la Piedra Formation, Deseadan age). The only known specimen is a juvenile with fragments of both dentaries, the right maxilla and a fragment of the left premaxilla with dentition. The loci and the number teeth preserved suggest a dental formula of I?3/i3, C1/c1, P3/p3, M?3/m?3.Fieratherium sorexhas a convergent shrew-like appearance and a unique combination of features among metatherians and other South American mammals of Palaeogene age, including the well-known faunas of Patagonia. An analysis of its phylogenetic affinities suggests thatFieratheriumis the sister-group of the Paucituberculata. As already described by other authors for several mammalian taxa, the mainly Patagonian South American Palaeogene fossil record offers little information to understanding the evolution of northern lineages.Fieratheriummay represent a taxon belonging to a lineage that had its origin in Neotropical regions, so far unrecorded in the southern region of South America. http://zoobank.org/urn:lsid:zoobank.org:pub:5F6D3A50-6345-4E66-BE3E-7FEF6CC66A9B [ABSTRACT FROM AUTHOR]