A unique, Late Oligocene shrew-like marsupial from western Argentina and the evolution of dental morphology.

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]