Hidden diversity of Palaeogene metatherians: a new family of polydolopimorphian marsupials from Peruvian Amazonia

South American marsupials are widely dominated by opossums and their kin today. Nevertheless, metatherian high-level taxonomic diversity was much higher before Pleistocene times. Here, we describe two new species and a new genus documenting the extinct order Polydolopimorphia, based on extensive material from Eocene–Oligocene localities of Peruvian Amazonia. Wamradolops telloi Stutz sp. nov. and Pozodolops manuelorum Stutz gen. et sp. nov. are morphologically close to the early Oligocene Wamradolops tsullodon Goin & Candela, 2004 from the same area. Parsimony analyses performed here strongly suggest that these three taxa document a new early-diverging clade of Polydolopimorphia, Wamradolopidae Stutz fam. nov., restricted to tropical–equatorial lowlands and falling outside the suborders Bonapartheriiformes and Polydolopiformes. These phylogenetic affinities further point to a Palaeocene–early Eocene ghost lineage for Wamradolopidae Stutz fam. nov., most probably at low latitudes of South America. Dental dimensions suggest that representatives of Wamradolopidae Stutz fam. nov. were extremely small, with estimated body masses ranging from 3 to 55 g. With cranial dimensions comparable to those of the living long-tailed planigale and Etruscan shrew, Wamradolops telloi Stutz sp. nov. is among the smallest mammals ever described.