Earliest South American paucituberculatans and their significance in the understanding of ‘pseudodiprotodont’ marsupial radiations

Abstract

We describe the oldest Paucituberculata marsupials, from the La Barda and Las Flores localities (Argentina; Late Paleocene and Early-Middle Eocene), as well as from the Itaboraí Basin (Brazil; Late Paleocene). The new taxa are represented by very scarce, though well-preserved, dental remains. A parsimony analysis was performed in order to evaluate the phylogenetic affinities of these taxa. Representatives of both Riolestes capricornicus n. gen. et sp. and Bardalestes hunco n. gen. et sp. appear as basal paucituberculatans, and their molar features give clues on the early evolution of the representatives of this order. Within the Paucituberculata we recognize two major clades: Canolestoidea and Palaeothentoidea. We conclude that “pseudodiprotodont” marsupials of the traditional literature (i.e., Polydolopimorphia + Paucituberculata) do not form a natural group.