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

Abstract

We describe a new metatherian mammal, Fieratherium sorex gen. et sp. nov., found in western Argentina (Quebrada Fiera locality, southern Mendoza Province), in late Oligocene deposits (Agua de la Piedra Formation, Deseadan age). Its type and only known specimen is small-sized and includes fragments of both dentaries, the right maxilla, and a fragment of the left premaxilla with dentition, all belonging to a single, juvenile individual. The loci and the number teeth preserved suggest a dental formula of I?3/i3, C1/c1, P3/p3, M?3/m?3. Fieratherium sorex has a convergent shrew-like appearance and a unique combination of features among metatherians, or any other South American mammal of Paleogene age, including the well-known faunas of Patagonia. An analysis of its phylogenetic affinities suggests that Fieratherium is the sister-group of the Paucituberculata. As already pointed out for several mammalian taxa, the mostly Patagonian, Paleogene South American fossil record hardly accounts for the radiation of northern lineages. Fieratherium may represent a taxon belonging to a lineage that had its origin in more Neotropical regions, thus unrecorded in the South America?s southernmost tip.