Off the script and crypt: the systematic affinities and evolutionary significance of an unexpected Sparassodonta (Mammalia, Metatheria) from Itaborai Basin (early Eocene)

The early Eocene Itaboraí fauna in southeastern Brazil has preserved two of the oldest known sparassodonts in South America, Patene simpsoni and Silvenator brasiliensis . Among the specimens assigned to Patene simpsoni , some differ in their significant smaller size, and in having separated paracone and metacone, flat labial borders of paracone and metacone, labial contact of the centrocrista on second lower molar, and a more elongated and less robust dentary. To test the taxonomic significance of these smaller specimens, we performed a PCA and a t-student test of lower molar measurements. The analyses showed that the smaller specimens do not overlap the morphospace of Patene simpsoni , which is an indicative of a new taxon, herein known as Xenocynus crypticus . The inclusion of Xenocynus in the concept of a phylogenetic analysis recovered that the differential dental features observed on this taxon represent synapomorphies for it in comparison with Patene . Some of Xenocynus dental features are convergent with the ones found on Hondadelphys and Stylocynus , two Miocene taxa. However, the presence of StC and large metaconids on m1-2 in Xenocynus confidently support these similarities as evolutionary convergence with these Miocene taxa. The dental features of X . crypticus suggest an insectivorous-carnivorous diet.