Dental anatomy, phylogenetic relationships and paleoecology of Orhaniyeia nauta (Metatheria, Anatoliadelphyidae), a Gondwanan component of the insular Eocene mammal fauna of Balkanatolia (north-central Turkey)

Two new specimens of the anatoliadelphyid metatherian Orhaniyeia nauta are described from the middle Eocene Uzunçarşıdere Formation in the Orhaniye Basin, north-central Turkey. These specimens augment our knowledge of the dentition of this taxon, revealing that P3 and p3 of Orhaniyeia resemble those of its sister taxon Anatoliadelphys in being enlarged and highly inflated, suggesting that both taxa consumed a durophagous diet. The ancestral dental morphology of anatoliadelphyids likely approximated that of Orhaniyeia nauta , whereas the dentition of Anatoliadelphys is autapomorphous. A phylogenetic analysis incorporating the new data for Orhaniyeia reconstructs anatoliadelphyids as nested among a diverse, but generally poorly documented, assemblage of early Paleogene bunodont Gondwanan marsupials that are typically allied with polydolopimorphians. Alternative phylogenetic reconstructions based on Anatoliadelphys alone have suggested either peradectid or protodidelphid affinities for anatoliadelphyids, but these hypotheses are not supported by the new data from Orhaniyeia . Anatoliadelphyids likely colonized Balkanatolia from the south (Africa/Arabia), even though there is no current fossil record indicating that this Gondwanan bunodont marsupial clade ever inhabited Africa/Arabia. The durophagous diet of Orhaniyeia was probably eclectic, but with an emphasis on gastropods. A similar dietary reconstruction has been proposed for the Australian Miocene marsupial Malleodectes , the dentition of which is remarkably convergent with that of Orhaniyeia . Orhaniyeia and Anatoliadelphys appear to have exploited distinct ecological niches, because the autapomorphous dentition of Anatoliadelphys includes multiple specializations for enhanced carnivory. The colonization of Balkanatolia by anatoliadelphyids instigated a small endemic radiation, a pattern that was replicated by multiple other Balkanatolian mammal clades.