Eutherian
Late Cretaceous (Maastrichtian)
Hell Creek Formation
McCone county
Montana, USA.

Eutherians represent the early evolutionary lineage that includes all modern placental mammals. During the Late Cretaceous, these mammals were typically small, nocturnal or crepuscular animals occupying ecological niches such as insectivory and omnivory within dinosaur dominated ecosystems.
7mm fully rooted eutherian tooth