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

Metatherians are members of the mammalian lineage that includes modern marsupials and their extinct relatives. During the Late Cretaceous, these small mammals inhabited forests, floodplains, and river systems, where they fed on insects, small vertebrates, fruits, and other available food sources.
7mm fully rooted metatherian tooth