Redescription of † Eobrasilia coutoi ( Metatheria : Polydolopimorphia ), a unique sclerocarpophagous metatherian from the Palaeogene of South America : Systematic affinities, and paleoecological and evolutionary implications

The 'Palaeogene strata' of the Itaboraí Basin (upper Paleocene-lower Eocene), Southeastern Brazil, has preserved 29 genera and almost 50 species of metatherians (about 65% of its mammalian diversity). Among them, Eobrasilia coutoi Simpson, 1947 is the most enigmatic due to its quite fragmentary nature. We redescribe this species by assigning new molars, first micro-CT and microwear data, and reinterpreting its systematic affinities. Eobrasilia coutoi weighed about 5.92 kg, thus representing the largest Palaeogene non-sparassodont metatherian from South America and Antarctica. A phylogenetic analysis recovered Eobrasilia and Periprotodidelphis as sister taxa (Eobrasiliidae rank nov.) within Polydolopimorphia. Lower molars morphofunctional variables (talonid relative area and height, and width by the length of the lower molar) suggest that E. coutoi has a pattern more similar to that of extant New World Primates (Cebidae, Pitheciidae) than extant didelphids. Buccolingually oriented wear facets on the parastyle and postmetacrista suggest a developed ectental masticatory component. Its microwear pattern is characterized by a predominance of fine scratches and small pits, resembling the pattern of callitrichids and cebids but differing from these in having longer scratches. Eobrasilia coutoi was likely a sclerocarpophagous metatherian, being able to exploit unripe fruits and seeds as food; however, it cannot be considered a specialized durophagous/hard-object feeder like extant pitheciines. The results suggest a Tropical humid 'mammalian trophic biome' for the localities in the Itaboraí Basin with Eobrasilia coutoi. This is consistent with an early Eocene age (likely contemporaneous to the Early Eocene Climatic Optimum) inferred for Itaboraí youngest faunal assemblage.