Systematics, dental specializations and paleoecology of Silvenator gen. nov., a small carnivorous metatherian (Mammalia, Sparassodonta) from the Paleogene Itaborai basin

The Itaborai fauna has preserved two of the oldest known sparassodonts in South America, Patene simpsoni and Nemolestes brasiliensis. Of these, Nemolestes brasiliensis has been identified by just two isolated lower molars. This article presents the first known m1 and dentary elements of this species. We have observed that this taxon differs from Nemolestes spalacotherinus due to the presence of several symplesiomorphies for Sparassodonta, such as a well-developed metaconid and closely spaced paraconid and metaconid on m2. A phylogenetic analysis recovered N. brasiliensis as the sister taxon of Nemolestes sp. indet. from Guabirotuba based on an abrupt increase in the dentary height at p3-m1 level. These two taxa were recovered as basal to a clade that comprehends Nemolestes spalacotherinus and all other sparassodonts (except for Mayulestes, Allqokirus and Patene). Therefore, we have assigned the Itaborai specimens to a new genus, Silvenator. This result provides further support that the Itaborai fauna has only preserved early lineages of Sparassodonta. A principal component analysis based on five morphofunctional indices in extant and extinct small carnivorous metatherians recovered a likely mesocarnivorous (faunivory) diet for Silvenator, thereby placing this taxon close to the thylacinid Badjcinus and, to a lesser extent, Allqokirus.