Late Cretaceous (Maastrichtian)

Hell Creek Formation

Powder River County, MT, USA

20mm jaw section with 4 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.  Few paleontologists specialize in these groups.  That’s why you see so many unidentified mammal fossils from the Cretaceous.

Most mammals from the Hell Creek Formation are either marsupials or multituberculates but there are also a few species of eutherian mammals.  After the K/T extinction it would be the eutherians that would better weather the storm and greatly diversify during the Early Cenozoic.