Late Cretaceous (Maastrichtian)
Hell Creek Formation
Powder River County, Montana, USA

30mm jaw section with 2 teeth.

Mammal,

The mammals of the Mesozoic belong to different groups than live today.  There were no rodents, rabbits, dogs, cats, bats, deer, cattle, horses, seals, nor whales so you need an expert schooled in groups of mammals most of us have never heard of and few paleontologists study.  That’s why you will see some unidentified mammals from the Cretaceous and why some that are identified elsewhere turn out to be misidentified.

Most mammals from the Hell Creek Formation are either marsupials or multituberculates but there are also a few species of eutherian mammals.  Some of these groups died out at the end of the Cretaceous along with the dinosaurs and some barely survived into the Cenozoic Era.